spectroscopy, Notas de estudo de Física

Baixe spectroscopy e outras Notas de estudo em PDF para Física, somente na Docsity! CHAPTER 1 Introduction This book was originally written to teach the organic chemist how to identify organic compounds trom the synergistic information afforded by the combination of mass (MS), infrared (IR), nuclear magnetic resonance (NMR), and ultraviolet (UV) spectra. Essentially, the molecule is perturbed by these energy probes and the moleçule's responses are recorded as spectra. Tn the present edition. the goal remains unchanged, but the format has evolvcd to respond to the remark- able evolution of instrumentation. NMR, without ques- tion, has become the most sophisticated tool available to the organic chemist, and it now requires four chapters to do it justice. In comparison, ultraviolet spectrometry has become relatively less useful for our purpose, and we havc discarded it despite nostalgic ties. We aim at a rather modest level of expertise in cach area of spectrometry, recognizing lhat the organic chemist wants to get on with the task of identifying the compound wilhout first mastering arcanc areas of elec- tronic engineering and quantum mechanics. But the al- ternative black-box approach is not acceptable either. We avoid these extremes with a pictorial, nonmathe- matical, vector-diagram approach to theory and instru- mentation. Since NMR spectra can be interpreted in ex- quisite detail with some mastery of theory, we present theory in corresponding detail —but still descriptive. Since an understanding of stereochemistry is essential to the concept of “chemical-shift equivalence,” we briefly revicw the relevant material. Even this modest level of expertise will permit so- Intion of a gratifying number of identification problems with no history and no other chemical or physical data. Of course, in practice other information is usually avail- able: the sample source, details of isolation, a synthesis sequence, or information on analogous material. Often, complex molecules can be identified because partial structures are known, and specific questions can be for- mulated; the process is more confirmation than identi- fication. In practice, however, difficulties arise in phys- ical handling of minute amounts of compound: trapping, clution from adsorbents, solvent removal, prevention of contamination, and decomposition of unstable com- pounds. Water, air, stopcock greases, solvent impurities, and plasticizers have frustrated many investigations. For pedagogical reasons, we deal only with pure or- ganic compounds. “Pure” in this context is a relative term, and all we can say is the purer, the better. A good criterion of purity for a sufficiently volatile compound (no nonvolatile impurities present) is gas chromato- graphic homogeneity on both polar and nonpolar sub- strates in capillary columns. Various forms of liquid- phase chromatography (adsorption and liquid-liquid columns. thin layer) are applicable to less volatile com- pounds. The spectra presented in this book were ob- tained on purified samples. In many cases, identification can be made on a frac- tion of a milligram, or even on several micrograms, of sample. Identification on the milligram scale is routine. OI course, not all molecules yield so casily. Chemical manipulations may be necessary but the information ob- tained from the spectra wil] permit intelligent selection of chemical treatment, and the energy probe method- ology can bc applied to the resulting products. When we proposcd in the first edition of this book that the synergistic combination of spectra sufficed to identify organic compounds, we did so in 177 pages after exploring the possibilities in a series of lectures at San Jose State University CA, in 1962. The methodology thus elab- orated was being rapidly adopted by practicing organic chemists, and we predicted that “in onc form or another, such material would soon become part of the training of every organic chemist.” Now every first-year organic text- book provides an introduction to spectrometry. References and problems arc provided at the end of cach chapter.* Chapter 8 presents several solved problems, and Chapter 9 has unsolved problems. The charts and tables throughout the text arc ex- tensive and are designed [or rapid, convenient access. They — together with the numerous spectra, including those of the problem sets —should furnish usefui ref- crence matcrial. * Specific references are provided as footnotes. General periodical reviews in spectrometry are available in Anafytical Chemistry and in Annual Reports of the Royal Society. CHAPTER 2 Mass Spectrometry 2.1 Introduction In the commonly used clectron-impact (EI) mode, a mass spectrometer bombards molecules in the vapor phase with a high-energy clectron beam and records the result of electron impact as a spectrum of positive ions separated on the basis of mass/charge (1/7); most of these ions are singly charged.* The mass spectrum of O benzamide cr nm, is presented as a com- puter-plot bar graph of abundâncc (vertical peak inten- sity) versus 7n/z (Fig. 2.1). The positive ion peak at m/z 121 represents the intact molecule (M) less one electron removed by the impacting beam and is designated the molecular ion, M**, The molecular ion in turn produces a series of fragment ions as shown for benzamide: o l ze Mm 121 CNH, +e- SE, |cH—C—NH, ganic compounds are described in Sections 2.7 and 210. In this chapter we describe mass spectrometry (MS) in sulficient detail to appreciate its application to or- ganic structure determination. For more details, mass spectrometry texts and spectral compilations arc listed at the end of this chapter. 2.2 Instrumentation E The minimum instrumental requirement tor the organic chemist is the ability to record the molecular weight of the compound under examination to the nearest whole number. Thus, the recording should show a peak at, say. mass 400, which is distinguishable from a peak at mass o 4 NH; º SP CH—C=0 mz 105 é 9 . + “cm EC, CNH, malz 44 mz 7 Various methods of producing molecular ions (in- cluding the EI method) are discussed in Section 2.5. De- tails of fragmentation patterns for representative or- * The unit of mass is the dalton (Day, defined as 1/12 ot the mass of an atom of the isotope !2C, which is arbitrarily 120000... mass units. 399 or at mass 401. In order to select possible molecular formulas by measuring isotope peak intensities (see Sec- tion 2.4), adjacent peaks must be cleanly separated. Ar- bitrarily, the valley between two such peaks should not be more than 10% of the height of thc larger peak. This degree of resolution is termed “unit” resolution and can be obtained up to a mass of approximately 2000 Da on readily available “unit-resolution” instruments.  (Vit + Voo) Vet + Vac) ta) FIGURE 2.4 (a). Schematic of quadrupole mass filter. Courtesy of Finnigan Corporation. rupole to the other without striking the poles; this os- cillation is dependent on the 17/z ratio of an ion. There- fore, ions of only a single m/z value will traverse the entire length of the filter at a given set of conditions. All other ions will have unstable oscillations and will strike the poles and be lost. Mass scanning is carried out by varying each of the rf and de frequencies while keep- ing their ratios constant. Hairpin Filament Endeap NE O rr Rin 415 Electrode 22 Instrumentation 5 2.2.4 Quadrupole Ion Storage (Fon Trap) (B.2) Essentially, the ion storage trap is a spherical configu- ration of the linear quadrupole mass filter. The opera- tions, however, differ in that the linear filter passes the sorted ions directly through to the detector, whereas the ion trap retains the unsorted ions temporarily within the trap. They are then released to the detector sequentially by scanning the electric field. These instruments are compact (benchtop), relatively inexpensive, convenient to use, and very sensitive. They also provide an inex- pensive method to carry out GC/MS/MS experiments (Section 2.2.7) (GC is gas chromatography). In general, the quadrupole instruments do not achieve the mass range and the high resolution of sector instruments. However, the mass range and resolution are adequate for unit-resolution mass spectrometry, and the rapid scan and sensitivity make them especially suit- able for use with capillary gas chromatography (Fig. 24b). 2.2.5 Time of Flight (C) In the time-of-flight (TOF) mass spectrometers, all sin- gly charged particles subjected to a potential difference V attain the same translational energy in electron volts (eV). Thus lighter particles have the shorter TOF over a given distance. The accelerated particles are passed into a field-free region where they arc separated in time by their m/z values and collected. Since arrival times between successive ions can be less than 107” s, fast elec- tronics are necessary for adeguate resolution. Time-of- flight devices are used with sophisticated ionizing meth- Electron Muttiplier Endcap Conversion Dynode FIGURE 244 (b). Quadrupole ion storage trap with attached gas chromatograph. The ionizing unit is external to the ion trap. With permission of the American Society of Mass Spectrametry. From “What is Mass Spectrometry?” 6 Chapter? Mass Spectrometry ods (FAB, laser desorption, and plasma desorption). Resolution is modest; sensitivity is high (Section 2.5.1.3). 2.2.6 FT-ICR (Fourier Transform-Ion Cyelotron Resonance) (D) (Also termed FT-MS) Tons generated by an electron beam from a heated fil- ament arc passed into a cubic cell where they are held by an electric trapping potential and à constant mag- netic field. Fach ion assumes a cycloidal orbit at its own characteristic frequency, which depends on m/z; the cell is maintained under high vacuum. Originally, these fre- quencics were scanned by varying the electric field until each cycloidal frequency was, in turn, in resonance with an applied constant radivlreguency. At resonance, the motion of the ions ol the same frequency is coherent and a signal can be detected. The newer instruments (Figure 2,4c) utilize a ra- diofrequency pulse in place of the sean. The pulse brings all of the cycloidal frequencies into resonance simulta- neously to yield a signal as an interferogram (a time- domain spectrum). This is converted by Fourier Trans- form to a [requeney-domain spectrum, which then vields the conventional »/z spectrum. Pulscd Fourier transform spectrometry applied to nuclear magnetic res- onance speetrometry is explained in Chapters 4 and 5. Since the resonanec can be measured with high ac- curacy, precise m/z values can be obtained, These values can yield unambiguous molecular formulas — a most de- sirablc goal: unfortunately, the instruments are still very expensive. Receiver plate = Trensmitter plate (“parent ions”) are separated in the first mass spectrom- eter and passed, one at a time, into the collision cham- ber where “daughter ions” are formed by collision with an introduced gas (helium): these ions arc passed into the second mass spectrometer, where a daughter-ion spectrum is produced. Thus. we have a mass spectrum of cach selected ion of the first spectrum — hence, MS/ MS. Ilybrid instruments are available with different types of spectrometers for the first and third stages. Typically lhese instruments are uscd for large mol- ecules and especially for the resolution ot mixtures. In a recent development, the ion trap is used to store a selected ion from electron impact (El) or chemical ion- ization (CI) by cjection of all of the other ions. This selected parent ion can then undergo collísion in the ion trap with an introduced gas (helium) and the daughter ions are ejected to the detector to furnish a daughter- ion spectrum. The collisions with the introduced gas are induced by subjecting the parent ions to a high-energy wavelorm. Thus MS/MS spectrometry is achieved within a single ion trap, rather than in three separate compartments, at an appreciable saving in cost. 2.3 The Mass Spectrum Mass spectra (ET) are routinely obtained at an clectron beam energy of 70 cV. The simplest event that occurs is the removal ot a single electron from the molecule in the gas phase by an clectron of the electron beam to form the molecular ion, which is a radical cation (M"'). For example, methano! forms a molecular ion in which the single dot represents the remaining odd electron: CHOH + e —> CH,OH* + 2e7 enfz 32 When the charge can be localized on one particular atom, the charge is shown on that atom: cH,ÓH compound. With unit resolution, this weight is the mo- lecular weight to the nearest whole number. A mass spectrum is a presentation of lhe masses of the positively charged lragments (including the molec- ular ion) versus their relative concentrations. The most intensc pcak in the spectrum, called the base peak, is assigned a value of 100%, and the intensities (height X sensilivity factor) of the other peaks, including the mo- Jecular ion peak, are reported as percentages of the basc peak. Of course, the molecular ion peak may sometimes be the base peak. In Figure 2.1, the molecular ion peak is m/z 121, and the base peak is n7/z 77. A tabular or graphic presentation of a spectrum may be used, A graph has the advantage of presenting patterns that, with experience, can be quickly recog- nized. However, a graph must be drawn so that Lhere is no difficulty in distinguishing mass units. Mistaking a peak al, say. 1m/z 79 for m/z 80 can result in lotal con- fusion, The molecular ion peak is usually the peak of highest mass number except for the isotopc pcaks. 24 Determination ofa Molecular Formula 2.4.1 Unit-Mass Molecular Ion and Isotope Peaks So far, we have discussed the mass spectrum in terms of unit resolutions: The unit mass of the molecular ion of C;H;NO (Fig. 2.1) is m/z 121 — that is, the sum of the unit masses of the most abundant isotopes: 7xC= a 7x!H=7 1x UN =I4 1x0 =16 Tn addition, molecular species exist that contain the less abundant isotopes, and these give use to the “iso- 24 Determination of a Molecular Formula 7 tope peaks” at M + 1,M + 2, ete. Im Figure 2.1, the M + 1 peak is approximately 8% of the intensity of the molecular ion peak, which for this purpose, is assigned an intensity of 100%. Contributing to the M + 1 peak are the isotopes, C, 2H, EN, and "O. Table 2.) gives the abundances of these isotopes relative to thosc of the most abundant isotopes. The only contributor to the M +2 peak of C,H,NO is "O, whose relative abun- dance is very low; thus the M + 2 peak is undetected. Ifonly C, H.N, O, F, P, and I are present, ihc approx- imate expected percentage (M + 1) and percentage (M 4 2) intensities can be calculated by use of the fol- lowing formulas: %(M + 1) = 1.1 X number of € atoms + 0.36 X number of N atoms : 2 %(M 42) = (LI x memo e vt € atoms) + 0.20 x number of O atoms Tí these isotope pcaks are intense enough to be measured accurately, the above calculations may be useful in determining the molecular formula.* *"There are limitations beyond the dilliculty of measuring small peaks: Lhe "CR2C ratio difters with the source of the compound—synthetic compared with a natural source. A natural product from different organisms or regions may show differences. Furthermore, isolope peaks may be more intense than (he caleulated valus because ofion- molecule interactions that vary with the sample concentration or with the class of compound involved. For example: o 1 [his represents transfer of a hydrogen atom from the excess of the compound to the molecular ion (see Section 2.10.:7.1 and Figure 2.14). Table 2.t Relative [sotope Abundances of Common Elements mem sa cm ar amem a Relutive Relutive Relativo Elements Isotope Abundance Isotope Ahundance Isotope Abundance Carbon o 100 EC um Hydrogen :H 100 *H 0016 Nitrogen “N 100 “N 0.38 Oxygen “O 190 “O 0.04 "O 020 Fluorinc NF 106 Silicon gi 100 si 510 “gi 335 Phosphorus SP 100 Sulfur 100 =s 0.78 4.40 Chlorine o] 100 325 Bromine “Br 100 98.0 Todine = 100 CHAPTER 1 Introduction This book was originally written to teach the organic chemist how to identify organic compounds trom the synergistic information afforded by the combination of mass (MS), infrared (IR), nuclear magnetic resonance (NMR), and ultraviolet (UV) spectra. Essentially, the molecule is perturbed by these energy probes and the moleçule's responses are recorded as spectra. Tn the present edition. the goal remains unchanged, but the format has evolvcd to respond to the remark- able evolution of instrumentation. NMR, without ques- tion, has become the most sophisticated tool available to the organic chemist, and it now requires four chapters to do it justice. In comparison, ultraviolet spectrometry has become relatively less useful for our purpose, and we havc discarded it despite nostalgic ties. We aim at a rather modest level of expertise in cach area of spectrometry, recognizing lhat the organic chemist wants to get on with the task of identifying the compound wilhout first mastering arcanc areas of elec- tronic engineering and quantum mechanics. But the al- ternative black-box approach is not acceptable either. We avoid these extremes with a pictorial, nonmathe- matical, vector-diagram approach to theory and instru- mentation. Since NMR spectra can be interpreted in ex- quisite detail with some mastery of theory, we present theory in corresponding detail —but still descriptive. Since an understanding of stereochemistry is essential to the concept of “chemical-shift equivalence,” we briefly revicw the relevant material. Even this modest level of expertise will permit so- Intion of a gratifying number of identification problems with no history and no other chemical or physical data. Of course, in practice other information is usually avail- able: the sample source, details of isolation, a synthesis sequence, or information on analogous material. Often, complex molecules can be identified because partial structures are known, and specific questions can be for- mulated; the process is more confirmation than identi- fication. In practice, however, difficulties arise in phys- ical handling of minute amounts of compound: trapping, clution from adsorbents, solvent removal, prevention of contamination, and decomposition of unstable com- pounds. Water, air, stopcock greases, solvent impurities, and plasticizers have frustrated many investigations. For pedagogical reasons, we deal only with pure or- ganic compounds. “Pure” in this context is a relative term, and all we can say is the purer, the better. A good criterion of purity for a sufficiently volatile compound (no nonvolatile impurities present) is gas chromato- graphic homogeneity on both polar and nonpolar sub- strates in capillary columns. Various forms of liquid- phase chromatography (adsorption and liquid-liquid columns. thin layer) are applicable to less volatile com- pounds. The spectra presented in this book were ob- tained on purified samples. In many cases, identification can be made on a frac- tion of a milligram, or even on several micrograms, of sample. Identification on the milligram scale is routine. OI course, not all molecules yield so casily. Chemical manipulations may be necessary but the information ob- tained from the spectra wil] permit intelligent selection of chemical treatment, and the energy probe method- ology can bc applied to the resulting products. When we proposcd in the first edition of this book that the synergistic combination of spectra sufficed to identify organic compounds, we did so in 177 pages after exploring the possibilities in a series of lectures at San Jose State University CA, in 1962. The methodology thus elab- orated was being rapidly adopted by practicing organic chemists, and we predicted that “in onc form or another, such material would soon become part of the training of every organic chemist.” Now every first-year organic text- book provides an introduction to spectrometry. References and problems arc provided at the end of cach chapter.* Chapter 8 presents several solved problems, and Chapter 9 has unsolved problems. The charts and tables throughout the text arc ex- tensive and are designed [or rapid, convenient access. They — together with the numerous spectra, including those of the problem sets —should furnish usefui ref- crence matcrial. * Specific references are provided as footnotes. General periodical reviews in spectrometry are available in Anafytical Chemistry and in Annual Reports of the Royal Society. CHAPTER 2 Mass Spectrometry 2.1 Introduction In the commonly used clectron-impact (EI) mode, a mass spectrometer bombards molecules in the vapor phase with a high-energy clectron beam and records the result of electron impact as a spectrum of positive ions separated on the basis of mass/charge (1/7); most of these ions are singly charged.* The mass spectrum of O benzamide cr nm, is presented as a com- puter-plot bar graph of abundâncc (vertical peak inten- sity) versus 7n/z (Fig. 2.1). The positive ion peak at m/z 121 represents the intact molecule (M) less one electron removed by the impacting beam and is designated the molecular ion, M**, The molecular ion in turn produces a series of fragment ions as shown for benzamide: o l ze Mm 121 CNH, +e- SE, |cH—C—NH, ganic compounds are described in Sections 2.7 and 210. In this chapter we describe mass spectrometry (MS) in sulficient detail to appreciate its application to or- ganic structure determination. For more details, mass spectrometry texts and spectral compilations arc listed at the end of this chapter. 2.2 Instrumentation E The minimum instrumental requirement tor the organic chemist is the ability to record the molecular weight of the compound under examination to the nearest whole number. Thus, the recording should show a peak at, say. mass 400, which is distinguishable from a peak at mass o 4 NH; º SP CH—C=0 mz 105 é 9 . + “cm EC, CNH, malz 44 mz 7 Various methods of producing molecular ions (in- cluding the EI method) are discussed in Section 2.5. De- tails of fragmentation patterns for representative or- * The unit of mass is the dalton (Day, defined as 1/12 ot the mass of an atom of the isotope !2C, which is arbitrarily 120000... mass units. 399 or at mass 401. In order to select possible molecular formulas by measuring isotope peak intensities (see Sec- tion 2.4), adjacent peaks must be cleanly separated. Ar- bitrarily, the valley between two such peaks should not be more than 10% of the height of thc larger peak. This degree of resolution is termed “unit” resolution and can be obtained up to a mass of approximately 2000 Da on readily available “unit-resolution” instruments.  (Vit + Voo) Vet + Vac) ta) FIGURE 2.4 (a). Schematic of quadrupole mass filter. Courtesy of Finnigan Corporation. rupole to the other without striking the poles; this os- cillation is dependent on the 17/z ratio of an ion. There- fore, ions of only a single m/z value will traverse the entire length of the filter at a given set of conditions. All other ions will have unstable oscillations and will strike the poles and be lost. Mass scanning is carried out by varying each of the rf and de frequencies while keep- ing their ratios constant. Hairpin Filament Endeap NE O rr Rin 415 Electrode 22 Instrumentation 5 2.2.4 Quadrupole Ion Storage (Fon Trap) (B.2) Essentially, the ion storage trap is a spherical configu- ration of the linear quadrupole mass filter. The opera- tions, however, differ in that the linear filter passes the sorted ions directly through to the detector, whereas the ion trap retains the unsorted ions temporarily within the trap. They are then released to the detector sequentially by scanning the electric field. These instruments are compact (benchtop), relatively inexpensive, convenient to use, and very sensitive. They also provide an inex- pensive method to carry out GC/MS/MS experiments (Section 2.2.7) (GC is gas chromatography). In general, the quadrupole instruments do not achieve the mass range and the high resolution of sector instruments. However, the mass range and resolution are adequate for unit-resolution mass spectrometry, and the rapid scan and sensitivity make them especially suit- able for use with capillary gas chromatography (Fig. 24b). 2.2.5 Time of Flight (C) In the time-of-flight (TOF) mass spectrometers, all sin- gly charged particles subjected to a potential difference V attain the same translational energy in electron volts (eV). Thus lighter particles have the shorter TOF over a given distance. The accelerated particles are passed into a field-free region where they arc separated in time by their m/z values and collected. Since arrival times between successive ions can be less than 107” s, fast elec- tronics are necessary for adeguate resolution. Time-of- flight devices are used with sophisticated ionizing meth- Electron Muttiplier Endcap Conversion Dynode FIGURE 244 (b). Quadrupole ion storage trap with attached gas chromatograph. The ionizing unit is external to the ion trap. With permission of the American Society of Mass Spectrametry. From “What is Mass Spectrometry?” 6 Chapter? Mass Spectrometry ods (FAB, laser desorption, and plasma desorption). Resolution is modest; sensitivity is high (Section 2.5.1.3). 2.2.6 FT-ICR (Fourier Transform-Ion Cyelotron Resonance) (D) (Also termed FT-MS) Tons generated by an electron beam from a heated fil- ament arc passed into a cubic cell where they are held by an electric trapping potential and à constant mag- netic field. Fach ion assumes a cycloidal orbit at its own characteristic frequency, which depends on m/z; the cell is maintained under high vacuum. Originally, these fre- quencics were scanned by varying the electric field until each cycloidal frequency was, in turn, in resonance with an applied constant radivlreguency. At resonance, the motion of the ions ol the same frequency is coherent and a signal can be detected. The newer instruments (Figure 2,4c) utilize a ra- diofrequency pulse in place of the sean. The pulse brings all of the cycloidal frequencies into resonance simulta- neously to yield a signal as an interferogram (a time- domain spectrum). This is converted by Fourier Trans- form to a [requeney-domain spectrum, which then vields the conventional »/z spectrum. Pulscd Fourier transform spectrometry applied to nuclear magnetic res- onance speetrometry is explained in Chapters 4 and 5. Since the resonanec can be measured with high ac- curacy, precise m/z values can be obtained, These values can yield unambiguous molecular formulas — a most de- sirablc goal: unfortunately, the instruments are still very expensive. Receiver plate = Trensmitter plate (“parent ions”) are separated in the first mass spectrom- eter and passed, one at a time, into the collision cham- ber where “daughter ions” are formed by collision with an introduced gas (helium): these ions arc passed into the second mass spectrometer, where a daughter-ion spectrum is produced. Thus. we have a mass spectrum of cach selected ion of the first spectrum — hence, MS/ MS. Ilybrid instruments are available with different types of spectrometers for the first and third stages. Typically lhese instruments are uscd for large mol- ecules and especially for the resolution ot mixtures. In a recent development, the ion trap is used to store a selected ion from electron impact (El) or chemical ion- ization (CI) by cjection of all of the other ions. This selected parent ion can then undergo collísion in the ion trap with an introduced gas (helium) and the daughter ions are ejected to the detector to furnish a daughter- ion spectrum. The collisions with the introduced gas are induced by subjecting the parent ions to a high-energy wavelorm. Thus MS/MS spectrometry is achieved within a single ion trap, rather than in three separate compartments, at an appreciable saving in cost. 2.3 The Mass Spectrum Mass spectra (ET) are routinely obtained at an clectron beam energy of 70 cV. The simplest event that occurs is the removal ot a single electron from the molecule in the gas phase by an clectron of the electron beam to form the molecular ion, which is a radical cation (M"'). For example, methano! forms a molecular ion in which the single dot represents the remaining odd electron: CHOH + e —> CH,OH* + 2e7 enfz 32 When the charge can be localized on one particular atom, the charge is shown on that atom: cH,ÓH compound. With unit resolution, this weight is the mo- lecular weight to the nearest whole number. A mass spectrum is a presentation of lhe masses of the positively charged lragments (including the molec- ular ion) versus their relative concentrations. The most intensc pcak in the spectrum, called the base peak, is assigned a value of 100%, and the intensities (height X sensilivity factor) of the other peaks, including the mo- Jecular ion peak, are reported as percentages of the basc peak. Of course, the molecular ion peak may sometimes be the base peak. In Figure 2.1, the molecular ion peak is m/z 121, and the base peak is n7/z 77. A tabular or graphic presentation of a spectrum may be used, A graph has the advantage of presenting patterns that, with experience, can be quickly recog- nized. However, a graph must be drawn so that Lhere is no difficulty in distinguishing mass units. Mistaking a peak al, say. 1m/z 79 for m/z 80 can result in lotal con- fusion, The molecular ion peak is usually the peak of highest mass number except for the isotopc pcaks. 24 Determination ofa Molecular Formula 2.4.1 Unit-Mass Molecular Ion and Isotope Peaks So far, we have discussed the mass spectrum in terms of unit resolutions: The unit mass of the molecular ion of C;H;NO (Fig. 2.1) is m/z 121 — that is, the sum of the unit masses of the most abundant isotopes: 7xC= a 7x!H=7 1x UN =I4 1x0 =16 Tn addition, molecular species exist that contain the less abundant isotopes, and these give use to the “iso- 24 Determination of a Molecular Formula 7 tope peaks” at M + 1,M + 2, ete. Im Figure 2.1, the M + 1 peak is approximately 8% of the intensity of the molecular ion peak, which for this purpose, is assigned an intensity of 100%. Contributing to the M + 1 peak are the isotopes, C, 2H, EN, and "O. Table 2.) gives the abundances of these isotopes relative to thosc of the most abundant isotopes. The only contributor to the M +2 peak of C,H,NO is "O, whose relative abun- dance is very low; thus the M + 2 peak is undetected. Ifonly C, H.N, O, F, P, and I are present, ihc approx- imate expected percentage (M + 1) and percentage (M 4 2) intensities can be calculated by use of the fol- lowing formulas: %(M + 1) = 1.1 X number of € atoms + 0.36 X number of N atoms : 2 %(M 42) = (LI x memo e vt € atoms) + 0.20 x number of O atoms Tí these isotope pcaks are intense enough to be measured accurately, the above calculations may be useful in determining the molecular formula.* *"There are limitations beyond the dilliculty of measuring small peaks: Lhe "CR2C ratio difters with the source of the compound—synthetic compared with a natural source. A natural product from different organisms or regions may show differences. Furthermore, isolope peaks may be more intense than (he caleulated valus because ofion- molecule interactions that vary with the sample concentration or with the class of compound involved. For example: o 1 [his represents transfer of a hydrogen atom from the excess of the compound to the molecular ion (see Section 2.10.:7.1 and Figure 2.14). Table 2.t Relative [sotope Abundances of Common Elements mem sa cm ar amem a Relutive Relutive Relativo Elements Isotope Abundance Isotope Ahundance Isotope Abundance Carbon o 100 EC um Hydrogen :H 100 *H 0016 Nitrogen “N 100 “N 0.38 Oxygen “O 190 “O 0.04 "O 020 Fluorinc NF 106 Silicon gi 100 si 510 “gi 335 Phosphorus SP 100 Sulfur 100 =s 0.78 4.40 Chlorine o] 100 325 Bromine “Br 100 98.0 Todine = 100 10 Chapter? Mass Spectrometry molecular ion peak, »:/z 180, and m/z 209 and 221 peaks resulting from reaction with carbocations, o A Ar CIT, Ar "CH, CH, —s HI +cH, Ar 34 Dimethoxyphenyt m/z 181 (base peak) o ! o A +H| 5H + A Ar CH, Ar CH, mvz 18 (molecular ion) O O A A —-CH, Ar cH, Ar CH, mz 209 o 9 * A FCMS — A +CH, Ar cH, Ar CH, mig 221 The energy content of the various secondary ions (ftom, respectively, CIL, isobutane, and ammonia) de- ercases in this order: CH; > CH! = NH, Thus by choice of “reagent” gas, we can control the tendency of the Cl-produced M | Hº ion to fragment. For example, when methane is the carricr gas, dioctyl phíhalate shows itsM + H' peak (m/z 391) as the base peak; more importantly, the [ragment peaks (e.g., mm/z 113 and 149) are 30-60% of the intensity of the base peak. When isobutane is used, the M + H' peak is large and the fragment peaks are only roughly 5% as intense as the M + H' peak. In many laboratories, the EL spectrum and the CI spectrum (with methane or isobutane) arc obtained rou- tinely since they are complementary. The CI spectrum will frequently provide the [M + H]* peak when the Ei spectrum shows only a weak or undetectable M*: peak. The [M — H]' peak may also appcar in the CI spectrum by hydríde abstraction. The CI fragmentation patterm is usually difficult to predict or rationalize. Note that the “nitrogen rule” (see Section 2) does not apply to the iM + HJ or the [M — HN* peaks; neither does it apply to the CI fragmentation ions. One general statement may be made: If a molecule MX (X is à functional group) is protonated by the re- agent ion to give the quasimolecular ion MXH', frag- mentation usually produces the neutral protonated functional group XH and the Tragment ion M'. Mass analyzer lon doam + Angle ot 5 incidence é so + a e Ls Atom beam Sample Fast atom gun FIGURE 25. Schematic for FAB mass spectrometry. The intense activity at the surface of the sample produces neutrals, sample ions, ions from the matrix, cte. Only the ions are accelerated toward the analyzer. MXH' —= M* + XH Thus an alcohol, ROH, is protonated to give ROH;*, which fragments with loss of a neutral molecule of water to give an R* peak.* 2.5.1.2 Field Desorption (FD) Stable molecular ions are obtained from a sample of low volatility, which is placed on the anode ol a pair of electrodes, between which there is an intense electric field. Desorption oc- eurs, and molecular and quasimolecular ions are pro- duced with insufficient internal energy for extensive fragmentation. Usually the major peak represents the IM + TJ ion. Synthetic polymers with molecular weighis on the order of 10,000 Da have been analyzed, but there is a much lower molecular weight limit for polar biopoly- mers; here the FAB procedure and others (see below) are superior. 2.5.1.3 Fast Atom Bombardment (FAB) Polar mol- ecules, such as peptides, with molecular weights up to 10,000 Da can be analyzed by a “soft” ionization tech- nigue called fast atom bombardment (FAB, Tig. 2.5). The bombarding beam consists of xenon (or argon) ai- cms of high translational energy (X€). This beam is pro- dueed by first ionizing xenon atoms with electrons to give xenon radical catíons: Xe Es xe! — 2e The radical cations are accelerated to 6-10 keV to give — radical cations ol high translational energy (Xe)'!, e Harrison (1992), Chapman (1993), or Watson (1985) in the ref- crenes al lhe end of this chapter. See also the review: Kingston. E. E., Shannon. J. S.. and Lacey, MJ. Org. Mass Spectront. TR, 18A— 192 (1983) 26 Use of the Molecular Formula. Index of Hydrogen Deficiency 11 which are then passed through xenon. During this pas- sage, the charged high-energy xenon obtains clectrons trom the xenon atoms to become high-energy atoms (Xe), and the Xe” ions are removed by an electric field. accelerato | <> Xe "> Xe't — — ct + Xe —> Xe + Ke'* The compound of interest is dissolved in a high-boiling viscous solvent such as glycerol; a drop is placed on a thin metal sheet, and the compound is ionized by the high-encrgy beam of xenon atoms (Xe). Ionization by translational energy minimizes the amount of vibra- tional excitation. and this results in less destruction of the ionized molecules. The polar solvent promotes ion- ization and allows diffusion of fresh sample to the sur- face. Thus ions are produced over a period of 20-30 min, in contrast to a few seconds for ions produced from solid samples. The molecular ion itself is usually not seen, but ad- such as [M + HJ" arc prominent. Other ad- s can be formed from salt impurities or upon addition of salts such as NaCl or KCl, which give IM + Na]: and [M + K]- additions. Glycerol adduct peaks are prominent and troublesome in the spectrum. Fragment ions are prominent and useful. 1.4 Electrospray Ionization (ESD Electrospray ionization involves placing an ionizing voltage — several kilovolts—across the nebulizer needle attached to the outlet from a high-performance liquid chromatograph (HPLC). This technique is widely uscd on water-soluble bio- molecules — proteins. peptides, and carbohydrates in particular. The result is a spectrum whose major peaks consist of the molecular ion with a different number of charges attached. A molecular ion ol, for example, about 10,000 Da with a charge (z) of 10 would behave in a mass spectrometer as though its mass were about 1000 daltons. Tis mass, therefore, can be determined with a spectrometer of modest resolution — and cost. Electrospray ionizatiou is onc of several variations of atmospheric pressure ionization (APT) as applied to thc outlet of au HPLC unit attached to Lhe inlet of the mass spectrometer. Thesc variations have in common the [ormation of a very fine spray (nebulization) from which the solvent can be quickly removed. The small particles are then ionized by a corona discharge at at- mospheric pressure and swept by the continuous low of the particles and a small clectrical potential that moves the positively charged particles through a small orifice into the evacuated mass spectrometer. 2.5.1.5 Matrix Assisted Laser Desorption/lonization (MALDI) In the MALDI procedure — used mainly for large biomolecules — the sample in a matrix is dis- persed on a surface, and is desorbed and ionized by the energy of a laser beam. The matrix serves the same pur- pose as it does in the FAB procedure (Section 2.5 “The MALDI procedure has been used recently in several variations to determine the molecular weight of large protein molccules — up to several hundred kDa. The combination of a pulsed laser bcam and a time-of- flight mass spectrometer (Section 2.2.5.) is particularly effective. Peptide sequencing is another application. Matrix selection is critical and depends on the wavelength of the laser beam and on the nature of the sample. Such polar compounds as carboxylic acids (e.g, nicotinic acid), urea, and glycerol have been used. At the time of writing, ES1 and MALDI are the preferred procedures for large biopolymers. 2.6 Useofthe Molecular Formula. Index of H'ydrogen Deficiency If organic chemists had to choose a single item ot infor- mation above all others that are usually available from spectra or from chemical manipulations, they would cer- tainly choose lhe molecular formula, In addition to the kinds and numbers of atoms. the molecular formula gives the index of hydrogen defi- cieney. The index of hydrogen deficiency is the number of pairs of hydrogen atoms that must be removed from the corresponding “saturated” formula to produce the molecular formula of the compound cf interest. The in- dex of hydrogen deficiency is also called the number of “sites (or degrees) of unsaturation”: this description is incomplete sincc hydrogen deficiency can result from cyclic structures as well as from multiple bonds. The index is Uus the sum of the number of rings. the number of double bonds, and twice the number of triple bonds. The index of hydrogen deficiency can be caleulated for compounds containing carbon, hydrogen, nitrogen, halogen, oxygen, and sulfur from the formula hyd) 5 Index = carbons — ee — halogens | nitrogens 2 2 Thus, the compound C)H;NO has an index of! 7 — 35+0.5+1=5. Note lhat divalent atoms (oxygen and sulfur) are not counted in the formula. For the gencralized molecular formula mB fnêiv. the index — TV — dl + SIM + 1, whcre +1 «isTL D, or halogen (ie., any monovalent atom) Bis O.S, or any other bivalent atom 12 chapter? Mass Spectrometry yis N.P, or any other trivalent atom ôis C, Si, or any other tetravalent atom The numerals I-IV designate the numbers of the mono», di-, tri-, and tetravalent atoms, respectively. For simple molecular formulas, we can arrive at the index by comparison of the formula of interest with iho molecular formula of the corresponding saturated com- pound, Compare C;H, and C;H 4; the index is 4 for the former and O for lhe latter. The index for C,H;NO is 5, and a possible structure Of course, other isomers (i.e,, compounds with the same molecular formula) are possible, such as HC=O0 NIL Note that the benzene ring itself accounts for four “sites of unsaturation”: three for the double bonds and once for the ring. Polar structures must be used for compounds con- taining an atom in a higher valence state, such as sulfur or phosphorus. Thus, if we treat sultur in dimethyl sulfoxide (DMSO) formally as a divalent atom, the calculated index, O, is compatible with the structure cH,—8-—cH,. We must use only formulas with filled — A 0: valence shells; that is, the Lewis octet rule must be obeyed. Similarly, if we treat the nitrogen in nitromethane as a trivalent atom, the index is 1, which is compatible / with CH, «Nº. TT we treat phosphorus in triphenyl- o phosphine oxide as trivalent, the index is 12, which fits (CoH9;P*— O-. As an example. let us consider the mo- lecular formula C,;H,N,0,BrS. The index of hydrogen deficiency would be 13 —- $$ +3+1=10 anda con- sistent structure would be NO, ON sen (O) (Index of hydrogen deficiency = 4 per benzene ring and 1 per NO, group.) The formula above for the index can be applied to fragment ions as well as to the molecular ion. When it is applied to even-electron (all electrons paired) ions, the result is always an odd multiple of 0,5, As an ex- ample, consider C,JT;O* with an index of 5,5, A reason- able structure is since 5; pairs of hydrogen atoms would be necessary to obtain the corresponding saturated formula C,H,,O (€,H.,,20). Odd-electron fragment ions will always give integer values of the index. Ierpenes often present a choice between a double bond and a ring structure. This question can readily be resolved on a microgram scale by catalylicaly hydro- genating the compound and rerunning the mass spec- trum. If no other easily reducible groups are present, the increase in the mass of the molecular ion peak is a measure of the number of donble bonds; and other “un- saturated sites” must be rings. Such simple considerations give the chemist very ready information about structure. As another example, a compeund containing a single oxygen atom might quickly be determined to be an ether or a carbonyl com- pound simply by counting “unsaturated sites.” 2.7 Fragmentation As à first impression, fragmenting a molecule with a huge excess of energy would seem a brute-force ap- proach to molecular structure. The rationalizations used to corrolate spectral patterns with structure, however, can only be described as elegant. though sometimes ar- bitrary. The insight of such pioncers as McLafferty, Beynon. Stenhagen, Ryhage, and Meyerson led to a number of rational mechanisms (or Lragmentation. These were masterfully summarized and elaborated by Biemann (1962), Budzikiewicz (1967), and others. Generally. the tendency is to represent the molec- ular ion with a delocalized charge. Djerassi's (1967) ap- proach is to localize the positive charge on either a q bond (except in conjugated systems), or on a hetero- atom. Whether or not this concept is totally rigorous, it is at the least a pedagogic rour de force. We shall use such locally charged molecular ions in this book. Structures A and B, [or example, represent the mo- lecular ion of eyclohexadiene. Compound A is a delo- calized structure with one less electron than the original uncharged dienc; both the electron and the positive Rearrangement peaks can be recognized by consid- cring the mass (m:/z) number [or fragment ions and for their corresponding molecular ions. A simple (no rear- rangement) cleavage of an even-numbered molecular ion gives an odd-numbered fragment ion and simple cleavage of an odd-numbered molecular ion gives an even-numbered fragment. Observation of a fragment ion mass different by 1 unit from that expected for a fragment resulting from simple cleavage (c.g., an even- numbered fragment mass from an even-numbercd mo- fecular ion mass) indicates rearrangement of hydrogen has accompanied fragmentation. Rearrangement peaks may bc recognized by considering the corollary to the “nitrogen rule” (Section 2.5). Thus, an even-numbered peak derived from an even-numbered molecular ion is a result of two cleavages. which may involve a rear- rangement. “Random” rearrangements of hydrocarbons were noted by the early mass spectrometrists in the petro- leum industry. For example, CH, CcH;—C—CE, | —> GH! CH, These rcarrangements defy straightlorward explana- tions. 2.9 Derivatives If a compound has low volatility or if the parent mass cannot be determined, it may be possible to prepare a suitable derivative. The derivative selected should pro- vide enhanced volatility, a predictable mode of cleav- age, a simplified fragmentation pattern, or an increased stability of the molecular ion. Compounds containing several polar groups may have very low volalility (c.g., sugars, peptides, and di- basic carboxylic acids). Acctylation of hydroxyl and amino groups and methylation of free acids are obvious and effective choices to incrcase volatility and give char- acteristic peaks, Perhaps less immediately obvious is the use of trimethylsilyi derivatives of hydroxyl, amino, sulfhydryl, and carboxylic acid groups. Trimethylsilyl derivatives of sugars and of amino acids are volatile enough to pass through GC columns. The molecular ion peak of trimethylsilyl derivatives may not always be present, but the M — 15 peak resulting from cleavage of one of the Si—CII, bonds is often prominent. Reduction of ketones to hydrocarbons has been used to elucidate the carbon skeleton of the ketone mol- 2.10 Mass Spectra of Some Chemical Classes 15 ecule, Polypeptides have been reduced with LiAIH, to give volatile polyamino alcohols with predictable frag- mentation patterns. Methylation and trifinoroacetyla- tion of tri- and teirapeptides have lcad to useful mass spectra. 2.10 Mass Spectra of Some Chemical Classes Mass speetra of a number of chemical classes are briefly described in this section in terms of the most useful gen- cralizations for identification. For more details, the rel- erences cited (in particular, the thorough treatment by Budzikiewicz, Djerassi, and Williams, 1967) should be consulted. Databases arc available both from publishers and as part of instrument capabilities. The references are selective rather than comprehensive. A table of fre- quently encountercd fragment ions is given in Appendix B. A table of fragments (uncharged) that are commonly eliminated and some structural inferences are presented in Appendix C. More exhaustive listings of common fragment ions have been compiled (see References). The cleavage patterns described here in Section 2.10 are for El spectra, unless stated otherwise, 2.10.1 Hydrocarbons 2.10.1,1 Saturated Hydrocarbons Most of the work early in mass spectrometry was done on hydrocarbons of interest to the petroleum industry. Rules 1-3, (Sec- tion 2.7) apply quite generally; rearrangement peaks, though common. are not usually intense (random re- arrangements), and numerous reference spectra are available, The molecular ion peak of a straight-chain, satu- rated hydrecarbon is always present, though of low in- tensity for long-chain compounds. The fragmentation pattern is characterized by clusters of peaks, and the corresponding peaks of each cluster are 14 (CH,) mass units apart. The largest peak in cach cluster represents a C,H,,., fragment and thus occurs at m/z = 14n + 1; this is accompanied by C,FL, and C,H,,., fragments. The most abundant fragments arc at C, and C,, and the tragment abundances deercasc in a smooth curve down to [M — C;Hs]*: the [M — CH.]' peak is characteristi- cally very weak or missing. Compounds containing more than eight carbon atoms show fairly similar spcc- tra; identification then depends on the molecular ion peak. Spectra ol branched saturated hydrocarbons are grossly similar to those of straight-chain compounds, but the smooth curve of decreasing intensitics is broken by preferred [ragmentation at each branch. The smooth 16 Chapier2 Mass Spectrometry Gs o 1) 20 30 40 50 60 7% & do 10 FIGURE 26 (a, b). tsomeric C,, hydrocarbons. curve for the r-alkane in Figure 2.69 is in contrast to the discontinuity at C,, for the branched alkane (Fig. 2.6b). “This discontinuity indicates that the longest branch of 5-methylpentadecane has 1Ô carbon atoms. In Figure 2.6b, the peaks at m/z 169 and 85 repre- sent cleavage on either side of the branch with charge retention on the substituted carbon atom. Subtraction of the molecular weight from the sum of these fragmenis accounts tor the fragment — CH—CH,. Again, we ap- preciate the absence of a C,, unit, which cannot form by a síngle cleavage. Finally, the presence of a distinct M — 15 peak aiso indicates a methyl branch. The frag- ment resulting from clcavage at a branch tends to lose a single hydrogen atom so that the resulting €, H,, peak is prominent and sometimes more intense than the cor- responding €,H,,,, peak. A saturated ring in a hydrocarbon increases the rel- ative intensity ofí the molecular ion peak and tavors cleavage at the bond connecting the ring to the rest of the molecule (rule 6, Section 2.7). Fragmentation of the ring is usually characterized by loss of two carbon atoms as GH, (28) and C,H, (29). This tendeney to lose even- numbered fragments, such as C,H,, gives a spectrum that contains a greater proportion of even-numbered mass ions than the spectrum of an acyclic hydrocarbon. n-Hexadecane CHACHoaCHs MW 226 120 130 10 150 160 170 180 190 20 210 220 28 toy $-Methyipentadecane crer p —— (CriopCtia Em | I 71169 Bs 120 130 10 150 160 170 150 150 20 210 220 23 ma to) As in branched hydrocarbons, C—C cleavage is ac- companied by loss of a hydrogen atom. The char- acteristic peaks are thercforc in the C,H,,., and C,H,, , series. The mass spectrum of cyclohexane (Fig. 2.6c) shows a much more intense molecular ion than those of acyclic compounds, since fragmentation requires the cleavage of two carbon-carbon bonds. This spectrum has its base + € too 4H so dd lohezona m Cyelohes p O + eo: CaMs te S41M) % of Base Peak o O 20 30 40 50 60 70 dO 90 100 no mfa FIGURE 26 (c). Cyclohexane. peak at m/z 56 (because of loss of C,H,) and a large peak at m/z 44, which is a fragment in the C,H,, ., series withn = 3. 2.10.1.2 Alkenes (Olefins) The molecular ion peak of alkenes, especially polyalkenes, is usually distinct. Location of the double bond in acyclic alkencs is diffi- cult because ol its facile migration in thc fragments. In cyclic (especially polyeyclic) alkenes, location of the double bond is frequently evident as a result of a strong tendency for allylic cleavage without much double-bond migration (rule 5, Section 2.7). Conjugation with a car- benyl group also fixes the position of the double bond. As with saturated hydrocarbons, aeyclic alkcncs are characterized by clusters of peaks at intervals of 14 units. In these clusters the C,H,,., and C,H,, pcaks are more intense than the C,H,,.,, peaks. The mass spectrum of B-myrcenc, a terpene, is shown in Figure 2.7. Lhe peaks at my/z 41, 55, and 69 correspond to the formula C,H,,., with a = 3, 4, and 5, respectively. Formation of the m/z 41 peak must involve rearrangement. The peaks at m/z 67 and 69 are the tragments from cleavage of a bi-allylic bond. m/z 69 | N, x a The peak at 12/z 93 may be rationalized as a struc- ture of formula C,H$* formed by isomerization (result- ing in increased conjugation), followed by allylic cleav- age. + — mz 93 Cyclic alkenes usually show a distinct molecular ion pcak. A unique mode of cleavage is the retro-Diels-Al- der reaction shown by limonene: 2.10 Mass Spectra of Some Chemical Classes 17 Cahs f-Myrcano 136tmj % of Base Paok o 1 20 30 40 50 60 70 80 90 100 MO 120 130 MO 150 me FIGURE 27. f-Myrcone. “s 2.10,1.3 Aromatic and Aralkyl Hydrocarbons An ar- omatic ring in a molecule stabilizes the molecular ion peak (rule 4, Section 2.7), which is usually sufficiently large that accurate intensity measurements can be made ontheM + 1 and M + 2 peaks, Figure 2.8 is the mass spectrum of naphthalene. The molecular ion peak is also the base pcak, and the largest fragment peak, m/z 51, is only 12.5% as intense as the molecular ion peak. A prominent peak (often the base peak) at 1v/z 91 (CoHsCH,*) is indicative of an alkyl-substituted ben- M 128(M) 100.00 129(M+1) ThoO 130(M+2) 0.40 % ok Base Peak O 10 20 30 40 50 60 70 80 90 100 NO 0 130 mz FIGURE 28. Naphthalene. 20 Chapter? Mass Spectrometry of a secondary alcohol can decompose further to give a moderately intense m/z 31 jon. H I I — RCH— CH GH e pó CS Bco, Som :0H qu qr Com OH Figure 2.9 gives the characteristic spectra of iso- meric primary, secondary. and tertiary €, alcohols. Benzyl alcohols and their substituted homologs and analogs constitute a distinct class. Generally the parent peak is strong. A moderate benzylic peak (M — OH) may be present as expected from cleavage 8 to the ring. A complicated sequence leads to prominent M — 1, M-2,and M — 3 peaks, Benzyl alcohol itself frag- ments to give sequentially the M — 1 ion, the CsH;* ion by loss of CO, and the CH, ' ion by loss of H.. cHLOW]|* oH —H. —CO =, co, m/z 108 mz 107 H. H H AH =H, H H H mz 79 miz 77 Ie IH" Loss of H,O to give a distinct M — 18 peak is a common feature, especially pronounced and mechanis- tically straightforward in some ortho-substituted benzy] aleohols. H, x Cc ES qt te É —s 2H H, H, Cl - ci, CX OH HO Ho, SS, pH The aromatic cluster at 1/z 77, 78, and 79 resulting trom complex degradation is prominent here also. [mcHa)* o-Ethylphenal 1221M) so so % of Base Peck so 30. O 10 20 30 40 50 60 70 80 90 100 TO 120 130 mia FIGURE 2.10. «-Ethylphenol. 2.10.2.22 Phenols A conspicuous molecular ion peak facilitates identification of phenols. In phenol itself, the molecular ion peak is the base peak, and the M — 1 peak is small. In cresols, the M - 1 peak is larger than the molecular ion as a result of a facile benzylic C—H cleavage. A rearrangement peak at m/z 77 and peaks resulting from loss of CO (M — 28) and CHO (M — 29) are usually found in phenols. oH SD CH mz 66 mz 65 The mass spectrum of a typical phenol is shown in Figure 2.10. This spectrum shows that a methyl group is lost much more readily than an « hydrogen. CHCH;] cn, Pa —SHy, a me HOT (100%) "OH CH—CH, 2.10.3 Ethers 2.10.3.1 Aliphatic Ethers (and Acetals) The molec- ular ion peak (two mass units larger lhan that of an analogous hydrocarbon) is small, but larger sample size usually will make the molecular ion peak or the M + 2.10 Mass Spectra of Some Chemical Classes 21 + cH==0H Ethyl sec—butyl ether Vi mw 102 100 CH % of Base Peak M -CHaCH;0 20 30 40 so 60 7 Bo 0 100 no mjz FIGURE 2.11. Ethyl sec-buiyl ether. 1 peak obvious (H- transfer during ion-molecule colli- One or the other of these oxygen-containing ions sion, see Section 2.4.1). may account for the base peak. In the case shown, The presence of an oxygen atom can be deduced the first cleavage (i.e., af the branch positions to lose from strong peaks at m/z 31, 45, 59, 73, .. . . These the larger fragment) is preferred. However, the peaks represent the RO* and ROCH,' fragments. first-formed fragment decomposes [urther by the Fragmentation occurs in two principal ways: following process, often to give the base peak (Fig. 2.11); the decomposition is important when the «a carbon is substituted (Sec McLatterty rearrange- ment, Section 2.8).* 1. Cleavage of the C—C bond next to the oxygen atom («, 8 bond, rule 8, Section 2.7) . AN A -RCH,CH, * A a RCH,—CH,=CH—O—CH,—CH;— > CHCH=6 CH, “creo, CHTÓH | Sto, | cH, H>cH, cH, In Figure 2.11,R = H. I CH —CH,—CH Í 7 a cH, 1 R o CH7O—CH,—CH, 2. €—O bond cleavage with the charge remaining on da the alkyl fragment. 5 + -ÓR' mz RLO—R' R = -CH;: a RCH—CH,—CH—6-(cH>cH, Cr, de RÔ ] RÓDR' SR"! cH, " HO The spectrum of long-chain ethers becomes dominated RCH,—CH,CH —0==CH, by the hydrocarbon pattern. [ y y' P: In Figure 21,R=Hme87 CH n Figure 2.11, o dnvz L. *Trans[er of the hydrogen atom by a four-membered ring mechanism I is an oversimplification. Deuterium labeling showed that three-, five-, and six-membered rings are also involved in longer chain compounds . + with relative dominance dependent on the compound. See Djerassi, RCH,—CH,CH— 04 CH, Co, and Fenselau, CJ. Am. Chem. Soc. 87, 5747 (1965); MeLatlerty, I U F. W. and Turecék, F. Interpretation of Mass Spectra. 4th ed. Mill cH, Valley. CA: University Science Books, 1993, pp. 261262. 22 Chapier? Mass Spectrometry Acetals are a special class of ethers. Their mass spectra are characterized by an extremely weak molec- ular ion peak, by the prominent peaks at M — R and M — OR, and a weak peak at M — H. Each of these cleavages is mediated by an oxygen atom and thus fac- ile. As usual, elimination of the largest group is pre- ferred. As with aliphatic elhers, the first-formed oxygen- containing fragments can decompose further with hydrogen migration and alkene elimination. H J = RT] ep OR H - [HÇ—oR + | + R—C—OR OR Kctals behave similarly. 210.32 Aromatic Ethers The molecular ion peak of aromatic ethers is prominent. Primary cleavage occurs at the bond $ to the ring, and the first-lormed ion can decompose further. Thus anisole, MW 108, gives ions of mi/z 93 and 65. n+ 9 -CO —D,cH, mz 108 mira mz. 65 The characteristic aromatic peaks at m/z 78 and 77 may arise from anisole as follows: H H LOy Sent, H HH H H H H H H 1 H H H o H mz 78 aniz 77 When the alkyl portion of an aromatie alkyl ether is C, or larger, cleavage £ to the ring is accompanied by hydrogen migration as noted above for alkylbenzenes. Clearly. cleavage is mediated by the ring rather than by the oxygen atom; C—C clcavage next to the oxygen atom is insignificant. Tm. mic 94 Diphenyl ethers show peaks at M - H,M — CO, and M — CHO by complex rearrangements. 2.10.4 Ketones 2.10.4.1 Aliphatic Ketones The molecular ion peak of ketones is usually quite pronounced, Major fragmen- tation peaks of aliphatic ketones resul from cleavage at the C—C bonds adjacent to the oxygen atom, the charge remaining with the resonance-stabilized acylium ion. Thus, as with alcohols and cthers, cleavage is me- diated by the oxygen atom. This clcavage gives rise lo a peak at m/z 43 or 57 or 71... . The base peak very often results from loss of the larger alkyl group. When one of the alkyl chains attached to the €=0 group is C, or longer, cleavage of the C—C bond once removed («,8 bond) from the C=0 group occurs wilh hydrogen migration to givc a major peak (McLafterty rearrangement). pH º ms 9 Açu RCN=SCHR RC CHR? =eHX bo H H E E R-CY SRA CH cH R Ro 2.10 Mass Spectra of Some Chemical Classes 25 + 100, €-c=o p-Chlorabenzophenene 90 Z16/M) 100.00 so + 217(M+1) 19.28 ci-g-czo 218(M+2) 33.99 470 n9(M+3) 6.2] ê 220M+4) 0.98 so + Ê CoHs mn 5 5 4 + ch 30 “o -M » Ma o [mm+2 | | | M+3 º I ) ir Mm+4 e pr so 60 70 80 90 10 NO 120 130 140 150 160 170 180 190 260 210 220 ma FIGURE 212. p-Chlorobenzopbenonc. The M peak is arbitrarily set in the table above at intensity 100% for discussion of the molecular ion cluster. Table 2.3 Intensities of Isotope Peaks (Relative to the Molecular Ion) for Combinations of Bromine and Chlorine Halogen % % % % % % Present M+2 M+4 M+ M+ M+ 10 M+12 Br 979 Br, 1950 95.5 Br; 2930 2860 934 ai 326 Ch 653 10.6 a 98 319 347 cu 1310 639 140 145 Cs 163.0 106.0 347 5.66 037 Cs 1960 1610 694 170 223 011 BrCl 1300 319 BrCl 280 1590 312 CLBr 1630 As 104 Nonanal 100 CHACH,);CHO Mw 142 8 Bo 70 5 & ê so " a g 40 * 3 20 Mess M-cHy= CH; 10 / MO M-1 0 20 30 “0 50 60 70 8o a 100 no 120 130 o 150 FIGURE 2.13. Nonanal. 26 Chapter? Mass Specirometry 2.10.6 Carboxylic Acids 210.61 Aliphatic Acids The molecular ion peak of a straight-chain monocarboxylic acid is weak but usually discernible. The most characteristic (sometimes the base) pcak is 1m/z 60 resulting from the McLaiferty re- arrangement. Branching at the « carbon enhances this cleavuge. Mel afferty rearrangement — so HOC), — HO—C) CH “cH b à In short-chain acids, peaks at M — OH and M — CO,H are prominent: these represent cleavage of bonds next to C=0, In long-chain acids, the spectrum consists of two series of pcaks resulting from cleavage at each C—C bond with retention of charge either on the oxy- gen-containing tragment (1n/z 45,59,73,87, . . Joron the alkyl fragment (1/2 29, 43,57,71.85, . . .). Aspre- viously discussed, the hydrocarbon pattern also shows pcaks at m/z 27,28; 41, 42,55, 56,69,70: .... In sum- mary. besides the McLatferty rearrangement peak, the spectrum of a long-chain acid resembles the series of “hydrocarbon” clusters at intervals of 14 mass units. In each cluster, however, is a prominent peak at CH, 10,. Hexanoic acid (MW 116), for example, cleaves as follows: o + | 2 A A Õ É + Q õ Bo o] co,H+ 59 (small) CH,CO,H- 87 (CH; CO,H! Dibasic acids are usually converted to esters to increase volalility. Trimethylsilyl esters are often suc- cessful. 2.10.6.2 Aromatic Acids The molecular ion peak of aromatic acids is largc. The other prominent pcaks are formed by loss of OH (M - 17) and of CO,H (M — 45). Loss of H;O (M — 18) is noted if a hydrogen-bear- Pra õ. Methyi octanoste | CHy(CHa)COCH, 100 co Ta tCHadefOCHa 90 CH, 8 EM tos (M+) 4:º 5 160:M+2) $ €0- ] Es ptctiicocEs 2 3 & 3 I (OCH MH 20 / - M Med 10 | M+2 o. | 4 1 11 Areeiro e qreeeeeeqeeregeramet 22 30 40 50 60 70 80 90 100 110 mjz FIGURE 2.14. Methyl actanoate. 130 140 150 160 ing ortho group is avaitable. This is one example of the general “ortho ctfect” noted when the substituenis can be in a six-membered transition state to facilitate loss of a neutral molecule of H,O, ROH, or NH.. Y where Z = OH, OR, NH,: Y = CH,, O, NH. 2.10.7 Carboxylic Esters 2.10.7.1 Aliphatic Esters The molecular ion peak of amethyl ester of a straighi-chain aliphatic acid is usually distinct. Even waxes usually show a discernible molec- ular ion peak. The molecular ion peak is weak in the range m/z 130 to — 200, but becomes somewhat more intense beyond this range. The most characteristic peak results from the familiar McLafferty rearrangement and cleavage one bond removed from the C—=O group. Thus a methyl ester of an aliphatic acid unbranched at the a carbon gives a strong peak at m/z 74, which, in fact, is the base peak in straight-chain methyl esters trom C, to Cy. The alcohol moiety and/or the « sub- stituent can often be deduced by the location of the peak resulting from this cleavage. | Hy / HM 7 A Aqur q | =R'CH=CUIR? L ROC Ss Cure ETC, ROC, CE a ke k MeLafferty rearrangement Four ions can result from bond cleavage next to C=0. pol ol RI-C—OR'] —>R and|[C—OR! La | R—C+OR'| —=|R—C| and-OR' 2.10 Mass Spectra of Some Chemical Classes 27 The ion R* is prominent in thc short-chain esters but diminishes rapidly with increasing chain length and is barely perceptible in methyl hexanoate. The ion R—C=o0 gives an easily recognizable peak for esters. In methy] esters it occurs at M — 31. It is the base peak in methyl acetate and is still 4% of the base peak in the o Cy methyl ester. The ions [OR 7* and forr arc usu- ally of líttle importance. The latter is discernible when = CH, (see m/z 59 peak of Fig. 2.14). First, consider esters in which the acid portion is the predominant portion of the molecule. The tragmenta- tion pattern for methyl esters of straight-chain acids can be described in the same terms used for the pattern of the free acid. Cleavage at each C—C bond gives an alkyl ion (1/2 29.43.57, . . . ) and an oxygen-contain- ing ion, C,Ho,. 10,* (59, 73, 87, . . .). Thus, there are hydrocarbon clusters at intervals of 14 mass units; in each cluster is a prominent peak at C,H,, 140,. The pcak (m/z 87) formally represented by the ion [CH,CH,;COOCH]* is always morc intense than its homologs, but lhe reason is not immediately obvious. However, it secms clear that the C,H,,. O, ions do not at all arise from simple cleavage. The spectrum of methy! octanoate is presented as Figure 2.14. This spectrum illustrates one difficulty in using the M + 1 peak to arrive at a molecular formula (previously mentioned, Section 2.4.1). The measured valuc tor the M+ 1 peak is 12%. The calculated value is 10.0%. The measured value is high because of an ion-molecule reaction because a relatively large sample was uscd to see the weak molecular ion peak. Now let us consider esters in which the alcohol por- tion is the predominant portion of the molecule. Esters of fatty alcohols (except methyl esters) climinate a mol- ecule of acid in the same manner that alcohois eliminate waler. A scheme similar to that described earlier for alcohols, involving a single hydrogen transfer to the al- cohol oxygen of the ester, can bc written. An alternative mechanism involves a hydride transfer to the carbonyl oxygen (McLafferty rearrangement). H Ração , RHC “cHG | R' ney, nd C—cH, CCO, pro. The preceding loss of acetic acid is so facile in ste- roidal acetates that they frequently show no detectable molecular ion peak. Steroidal systems also seem um- usual in thal they often display significant molecular ions as alcohols, even when the corresponding acetates do not. 30 Chapier? Mass Spectrometry RCH;SGRENH—CHCHR' tr, R” z 44, more intense 1, m/z 30, less intense Cleavage of amino acid esters occurs at both C— € bonds (a, b below) next to the nitrogen atom, loss of the carbalkoxy group being preferred (a). The aliphatic amine fragment decomposes further to give a peak at mz 30. b a GH CoOR" 2 RcHCH-CH--COOR' NH, NH, ido NH, RCHCH,CH NH, NH, [rretmem CH=NH, mz NM) 210.92 CyelicAmines In contrast to acyclic amines, the molecular ion peaks of cyclic amines arc usually in- tense unless there is substitution at the « position; for example, the molecular ion peak ol pyrrolidine is strong. Primary cleavage at the bonds next to the N atom leads either (o loss of an a-hydrogen atom to give astrongM — 1 peak or to opening of the ring; the latter event is followed by elimination of ethylene to give *-CH,NH=CIL (m/z 43, base peal), hence by loss of à hydrogen atom to give CH;=N==CH, (m/z 42). N- Methyl pyrrolidine also gives a C,H,N' (m/z 42) peak, apparently by morc than one pathway. Piperidine likewisc shows a strong molecular ion and M — 1 (basc) peak. Ring opening followed by sev- eral availabic sequences leads to characteristic peaks at mz 70, 57, 56, 44, 43, 42, 30, 29, und 28. Substituents are cleaved from the ring (rule 6, Section 2.7). 2.10.9.3 Aromatic Amines (Anilines) The molecular ion peak (odd number) of an aromatic monoamine is intense, Loss ol onc of the amino H atoms of aniline gives a moderately intense M — 1 peak; loss of à neu- tral molecule of HCN followed by loss of a hy- drogen atom gives prominent peaks at m/z 66 and 65, respectively. Tt was noted above Lhal cleavage of alkyl aryl ethers occurs with rearrangement involving cleavage of the ArO—R bond; that is, cleavage was controlled by the ring rather than by the oxygen atom. In the case of alkyl aryl amines, cleavage of the C—€ bond next to the nitrogen atom is dominant; that is, the heteroatom con- trols cleavage. H-LCL>CHR SC, mz 106 210.10 Amides 2.10.10.1 Aliphatic Amides The molecular ion peak of straight-chain monoamides is usually discerníble. The dominant modes of cleavage depend on thc length of the acyl moiety, and on the lengths and number of Lhe alkyi groups attached to the nitrogen atom. The base peak in all straight-chain primary amides higher than propionamide results from the familiar McLafferty rearrangement, + Ho MH :0p ACHAR ci=cnr : a and aN Ao gm 2 No . Sex >éH, H, nvz so Branching at the « carbon (CH, ete.) gives a homolo- gous peak atrm/z 7301 87,.... Primary amides give a strong peak at m/z 44 from cleavage of the R—CONH, bond: (0=C—NH, — 0=C==NH,): this is the base peak in C,—C, primary amides and in isobulyramide. A moderate peak at m/z 86 results from y,8€— Celeav- age, possibly accompanied by cyclization, Secondary and tertiary amides with an available hy- drogen on the y-carbon of the acyl moiety and methyl groups on the N atom show the dominant peak resulting from the MeLafferty rearrangement. When the N-alkyl groups are C, or longer and the acyl moiety is shorter than C,, another mode of cleavage predominates. This is cleavage of the N-alkyl group £ to the N atom, and cleavage of the carbonyl C—N bond with migration of an a-hydrogen atom of thc acyl moiety. | Re C—nHLcaNER DEE, R—CH, o Cp Ateu, AE=t=o, fg, H, R-CLH m/230 d 2.10.10.2 Aromatic Amides Benzamide (Fig. 2.1) is a typical example. Loss of NH, from the molecular ion yields a resonance-stabilized benzoyl cation that in tum undergoes cleavage to a pheny] cation. :0"! mo 1 Mi, cHc=0:0,cHs mz Os mz 77 | CH—CNH, mz A separate fragmentation pathway gives rise to a mod- est m/z 44 peak. -CH! s lo. CH—C—NH, CONH,+ m/z 44 2.10.11 Aliphatic Nitriles The molecular ion peaks of aliphatic nitriles (except for acetonitrile and propionitrile) are weak or ab- sent, but the M + 1 peak can usually be located by its behavior on increasing inlet pressure or decreasing repeller voltage (Section 2.5). A weak but diagnostically useful M — 1 peak is formed by loss ot an a hydrogen to form the stable ion: RCH—C=N't — RCH=C==N-. The base peak of straight-chain nitriles betwcen €, and C, is mz 41. This peak is the ion resulting from hydrogen rearrangement in a six-membered transition state. 2.10 Mass Spectra of Some Chemical Classes 31 MeLafferty rearrangement AA nf Porto c c “cH, “CH, mz However, this peak lacks diagnostic valuc because of the presence of the CH, (1/2 41) for all molecules con- taining a hydrocarbon chain, A peak at m/z 97 is characteristic and intense (sometimes the base peak) in straight-chain nitriles Cs and higher. The following mechanism has been de- picted: mz 97 Simple cleavage at each C—C bond (except the one next to the N atom) gives a characteristic series of homologous pcaks of even mass number down the en- tire length of the chain (m/z 40, 54, 68, 82. . . .) result- ing from the (CH,),C=Nº ions. Accompanying these peaks are the usual peaks of the hydrocarbon pattern. 2.10.12 Nitro Compounds 2.10.12.1 Aliphatic Nitro Compounds The molecu- lar jon peak (odd number) of an aliphatic mononitro compound is weak or absent (except in the lower hom- ologs). The main pcaks are attributable to the hydro- carbon fragments up to M — NO». Presence of a nitro group is indicated by an appreciable peak at m/z 30 (NO) and a smaller peak at mass 46 (NO, '). 2.10.12.22 Aromatic Nitro Compounds The molccu- lar ion peak of aromatic nitro compounds (odd number tor one N atom) is strong. Prominent peaks result from elimination of an NO, radical (M — 46, the base peak in nitrobenzene), and of a neutral NO molccule with rearrangement to form the phenoxy cation (M — 30); 32 Chapicr? Mass Spectrometry both are good diagnostic pcaks. Loss of HC==CH from the M — 46 ion accounts for a strong peak at M — 72: loss af CO from the M — 30 ion gives a peak atM — 58. A diagnostic peak at m/z 30 results from the NO" ion. “The isomeric 0-, 4n-, and p-nitroanilines each give a strong. molecular ion (even number). They all give prominent peaks resulting from (two seguences, NO, N mz 138 (M) ==> miz 92 > mvz 65 =NO, -€o |-so, mz 108 ——> péz BO Aside from differences in intensities, the three isomers give very similar spectra. Fhe meta and para compounds give a small peak at »/z 122 from loss of an O atom, whereas the ortho compound eliminates - óH as follows to give a small peak at m/z 121. 2.10.13 Aliphatic Nitrites The molecular ion peak (odd number) of aliphatic ni- trites (one N present) is weak or absent. The peak at m/z 30 (NO) is always large and is often the base peak. There is a large peak at mz 60 (CH, ONO) in all nitrites unbranched at the a carbon; this represents cleavage of the C—€ bond next to the ONO group. An a branch can be identilicd by a peak at »u/z 74, 88, or 102..... Absence of a large peak at m/z 46 permits differentiation [rom nitro compounds. Hydrocarbon peaks are prominent, and their distribution and inten- sities describe the arrangement of the carbon chain. 2.10.14 Aliphatic Nitrates The melecular ion peak (odd number) of aliphatic ni- trates (one nitrogen present) is weak or absent. À prom- inent (frequently the base) peak is formed by cleavage of the C—C bond next to the ONO; group with loss of the heaviest alkyl group attached to the « carbon. where R > R'. The NO,: peak at 1m/z 46 is also prom- inent. As in the case of aliphatic nitrites, the hydrocar- bon fragment ions are distincl 2.10.15 Sulfur Compounds “The contribution (4.4%, see Table 2.2 and Fig. 2.15) of the “S isotope to the M +2 peak, and often to a (fragment + 2) peak, affords ready recognition of sul- fur-containing compounds. A homologous series of sul- fur-containing fragments is four mass units higher than the hydrocarbon fragment series. The number of sulfur atoms can be determined from the size of the contri- bution of the *S isotope to the M + 2 peak. The mass of the sulfur atom(s) present is subtracted from the mo- lecular weight. In diisopentyl disulfide, for example, lhe molecular weight is 206, and the molecule contains two sulfur atoms. The formula for the rest of the molecule is therefore found under mass 142, that is, 206 — (2 x 32). 2.10.15.1 Aliphatic Mercaptans (Thiols) The molec- ular ion peak of aliphatic mercaptans, except for higher terliary mercaptans, às usually strong enough so that the M + 2 peak can be accurately measured. In general, the cleavage modes resemble those of alcohols. Cleavage of the C—C bond («,8 bond) next to the SH group gives the characteristic ion cH=SH —s éH,—SH (mz 47). Sulfur is poorer than nitrogen, but better than oxy- gen, at stabilizing such a fragment. Cleavage at the By bond gives a peak at m/z 61 of about one-hall the in- tensity of the m/z 47 peak. Cleavage at the y,ô bond gives a small peak at 2n/z 75, and elcavage at the 8, bond gives a peak at m/z 89 that is more intense than the peak at 1/2 75; presumably the n1/z 89 ion is stabi- lized by cyelization: Again analogous to alcohols, primary mercaptans split out H;S to give a strong M — 34 peak, the resulting ion then eliminating ethylene; thus the homologous se- riesM — H;S — (CH,=CH,), arises. SR Hj S-H fm eo CH; —cHRj' to, Secondary and tertiary mercaptans cleave at the o- carbon atom with loss of the largest group to give a prominent peak M- CH, M-CH, M-— CH, ... . However, a peak atm/z 47 may also ap- pear as a rearrangement peak of secondary and tertiary 35 2.10 Mass Spectra of Some Chemical Classes M M m| |M+2 M+2 M+2 M+4 [a +4 p +6 ci ct, [A M+2 m| |m+2 M+2 M+2 M+4 M m M+4 M M+4 M+4 6 |"+e | + Br Brel BrCh, BrCI, M+2 M+2 M+2] ms4 M+2] JM+4 M+4 ' M M+4 mM u M+6 M+6 M+6 pm +8 E +8 Br Br,C1 BrsCl, BraCy M+2] |M+4 m+4 M+4 M+4 M+2 m+2 u+6 + M+6 m+2 M+6 v M+6 N M u M+8 | [º +8 | Br, Br;Ct BrsCly BrsC1, (a) — miz FIGURE 2.16 (4). Peaks in the molecular ion region of bromo and chloro compounds. Contributions due to C, H. N, and O arc usualy small compared Loss of HCI occurs, possibly by 1,3 elimination, to give a peak (weak or moderate) at M — 36. 1n general, the spectrum of an aliphatic monochlor- ide is dominated by the hydrocarbon pattern to a greater extent than that of à corresponding alcohol, aminc, or mercaptan. 2.10.16.2 Aliphatic Bromides The remarks under al- iphatic chlorídes apply quite generally to the corre- sponding bromides. 2.10.16.3 Aliphaticlodides Aliphaticiodides give the strongest molecular ion peak of the aliphatic halide: Since iodine is monoisotopic, there is no distinctive iso- to those for Br and CI. tope peak. The presence of am iodine atom can some- times be deduecd from isotope peaks that are suspi- ciously low in relation to the molecular ion peaks. and from several distinctive peaks: in polyiodo compounds, the large interval between major peaks is char: +ristic. lodides cleavo much as do chlorides and bromides, but the CH, I ion is not as cvident as the corresponding chloride and bromide ions. 2.M.16.4 Aliphatic Fluorides Aliphatic Quorides give the weakest molecular ion peak of the aliphatic halides. Fluorine is monoisotopic, and its detection in polyfluoro compounds depends on suspiciousiy small isotopic peaks relative to the molecular ion, on the in- 36 Chapter? Mass Spectrometry Carbon tetrachloride CC 100 Mw 152 tb) Cel Ca % of Base Peak a s 2 30 40 50 60 70 8 90 myz FIGURE 216 (5). Carbon tetrachloride (cf. Fig. 2.164). tervals between pcaks, and on characteristic peaks, Of these, the most charactoristic is 7m/z 69 resulting from the jon CH;*, which is the base pcak in all perfluoro- carbons. Prominent pcaks are noted at m/z 119, 169, 219... : these are increments of CF, The stable ions C;F;' and CF; give large peaks at m/z 13! and 181. “The M — F peak is frequently visible in perfiuorinated compounds. In monoflnorides, cleavage of the «8 €—C bond is less important than in the other mono- halides, but cleavage of a C—H bond on the «-carbon atom is more important. This reversal is a consequence of the high electronegativity of the F atom and is ratio- nalized by placing the positive charge on lhe e-carbon atom, The secondary carbonium ion thus depicted by a loss of a hydrogen atom is more stable than the primary carbonium ion resulting trom loss of an alkyl radical, [R—CH, —FI Lo Rº 2.10.16.5 Benzy] Halides The molecular ion peak of benzy! halides is usually detectable. The benzyl (or tro- pylium) ion from loss of the halide (rule 8, Section 2.7) is favored even over 8-bond cleavage of an alkyl sub- stitucnt. A substituted phenyl ion (a-bond cleavage) is prominent when the ring is polysubstituted. Hp CH—F > CIL—E 2.10.16.6 Aromatic Halides The molecular ion peak of an aryl halide is readily apparent. The M — X peak is large for all compounds in which X is attached directly to the ring. 2.10,17 Ifeteroaromatic Compounds The molecular ion peak of heteroaromatics and alkyl- ated heteroaromatics is intense. Cleavage ol the bond | tree eee geeeeeeeeerteeeereee ereto otooeeermererempereempeemmm 100 110 120 130 140 150 160 Bto the ring, as in alkylbenzencs, is the general rule; in pyrídine, the position of substitution determines the ease of cleavage of the 8 bond (see below). Localizing the charge of the molecular ion on the heteroatom, rather than in the ring a structure, provides a satisfactory rationale for the observed mode of cleav- age. The present treatment follows that uscd by Djerassi (Budzikiewicz et al., 1967). The five-membered ring heteroaromatics (furan, thiophene, and pyrrole) show very similar ring cleavage patterns. The first step in each case is cleavage of the carbon-heteroatom bond. TT. LT -CH=Y = | A ho | VN | mz 39 o Do Hc=Y RR | q! tal CHAN y where Y=O0,8, NH; td wherc Y — 8, NH, Thus, furan exhibits two principal peaks: C)H,! (m/z 39) and HC O (1/2 29). For thio- phene, there arc three peaks, C,H;! (1m/z 39), HC (m/z 45), and C, 5 (m/z 58). And for pyrrole, there are three peaks: C,H,* (1/2 39), Hi NH (mz 28) and CALNH (mz 41). Pyrrole also climinates a neutral molecule of HCN to give an intense peak at m/z 40. The basc peak of 2,5-dimethylfuran is 1/z 43 (CH;C= à. yo. + Cleavage of lhe 8 C—C bond in alkylpyridines de- pends on the position of ihe ring substitution, being more pronounced when the alkyl group is in the 3 po- sition. An alkyl group of more than three carbon atoms in the 2 position can undergo migration of a hydrogen atom to the ring nitrogen. Co NO DC ud cH, d Cm B bon: co 2 “A As Nº ÉH, H A similar cleavage is [ound in pyrazines since all ring substituents are necessarily ortho to one of the ni- trogen atoms. 2.10.18 Natural Products 2.10.18.1 Amino Acids Detection of the molecular ion peaks of amino acids can be difficull. H we examine the mass spectra of amino acids, as well as of stcroids and triglycerides, by a variety ol ionization techniques, we can appreciate their relative merits. The EI spectra of amino acids (Fig. 2.174) or their esters give weak or nonexistent molecular ion peaks, but CI and FD (Fig. 2.17b and c) give cither molecular or quasimofecular ion peaks. The wcak molecular ions in the EI spectra arise sinec amino acids easily lose their carboxyl group and the esters easily lose their carboal- koxyl group upon electron impact. o, no “com Seco EM, p.cH=NH, EL 5 - R—CH M 45 a Cm N 0 Vo «CORY Sron' COL, p-cH=NH, EI nc M-(a6 + RO The FD fragmentation pattern for leucine shows an MIL (m/z 132) ion, that readity loses 4 carboxyl group 210 Mass Spectra of Some Chemical Classes 37 a 1007 Ê Ha€ o Ntia DcnenacH Ha€ —— €OoH sor 30 a õ % of Base Peak » o ” o so 100 150 my Leucine, M=13], El 1007 % of Base Peak 5 5 8 » o 50 100 150. miz Leucine, M=131, CI (Isobutane, 200" C) so 100 150 my Leucine, M=131, FD(12 MA) FIGURE 2.17. Mass spectra of leucine. (2) Electron impact (EI). (b) Chemical ionization (CT). (e) Field desorption (FD). G co,H (CH CHCH,CÃA NH, (COM), oa (CH). CHCELG xAM antz 87 HH pe (CH), CHCH;CH=NH, mz 86 to form the m/z 87 ion, which in tum loses a hydrogen atom to form the mz 86 ion. 40 Chapter? Mass Spectrometry Data and Spectral Compilations American Petroleum Institute Research Project 44 and Yher- modynamics Research Center (formerly MCA Research Project). (1947 to dale). Catalog of Selected Mass Spectral Data. College Station, TX; Texas A & M University, Dr. Bruno Zwolinski. Director. ASTM (1963). “Index of Mass Spectral Data” American So- ciety for Testing and Materials. STP-356, 244 pp. ASTM (1969). “Index of Mass Spectral Data,” American So- ciety for Testing and Materials, AMD 17, 632 pp. Beynon, J. H., and Williams, A. E. (1963). Mass and Abun- dance Tables for Use in Mass Spectrometry. Amsterdam: Elsevier. Beyon, J. H., Saunders, R. A. and Williams, A. E. (1965). Table of Meta-Stable Transitions. New York: Elsevier. Comu, A.. and Massot, R. (1966). Compilation of Mass Spec- iral Data. London: Heyden. Supplements issued (1992). Eight Peak Index of Mass Spectra, 4th ed. Boca Raton, FL: CRC Press. (1974). Handbook of Spectroscopy, Vol. II, Cleveland: CRC Press, pp. 317- 330. Electron impact data for 15 compounds in cach of 16 classes of organic compounds. Heller, S. R., and Milne, G. W. EPA/NIH Mass Spectral Search System (MSSS), A Division of CIS. Washinglon, DC: U.S. Government Printing Office, An interactive com- puter searching system containing Lhe spectra of over 32,000 compounds. These can be scarched on the basis of peak intensities as well as by Biemann and probability matching techniques. MeLullerty, F. W. (1982). Mass Spectra! Correlations, 2nd ed. Washington, DC: American Chemical Socicty. McLafferty. F. W., and Penzelik, J. (1967). Index and Bibli- ography of Mass Specirometry, 1963-1965. New York: Wi- ley-Interscience. McLalfferty, F. W., and Stauffer, 1D. 8. (1988). The Wiley/NBS Registry of Mass Spectral Data (7 volumes). New York: Wi- ley-Interscience. MeLatterty, F. W., and Stauffer, D. B. (1992). Registry of Mass Spectral Data, Sth ed. New York: Wiley. Magnetic disc, hard disc, or CD-ROM, 220,000 spectra. Problems Melaiferty, F. W., and Stauffer, D. B. (1991). The Important Peak Index of the Registry of Mass Spectra! Data, 3 Vols New York: Wiley. Slenhagen, E.. Abrahamsson, S., and McLafferty. F., Eds. (1969). Arias of Mass Spectral Data. New York: Wiley-In- terscience, The three volumes have complete El data for about 6000 compounds. Stenhagen, E., Abrahamsson, S., and McLalferty, F., Eds. (1974). Registry of Mass Spectral Data. New York: Wiley- Interscience, The four volumes contain bar graphs of 18,806 compounds. Volume IV also contains the index Tor all four volumes. Special Monographs Harrison, G. (1992). Chemical Ionization Muss Spectrometry, 2nd cd. Boca Raton, FL: CRC Press. Linskens, H. F., and Berlin, J. Eds. (1986). Gas Chromatog- raphy-Mass Specirometry. New York: Springer-Verlag. March. R. E. and Hughes, R. 1. (1989). Quadrupole Storage Mass Spectrometry. New York: Wiley-Interscience. McFadden, W. H. (1973). Techniques of Combined Gas Chro- matography'Mass Spectrometry: Applications in Organic Analysis. New York: Wiley-Interscience. McLalferty, F. S. (1983). Tandem Muss Spectrometry, 2nd ed. New York: Wiley-Interscience. Message. G. M. (1984). Practical Aspecis of Gas Chromarog- raphy-Mass Spectrometry, New York: Wiley. Porter, Q. N., and Baldas, J. (1971). Mass Spectrometry of Hetervcyelic Compounds, in A. Weissberger and E. C. Tay- lor (Eds.), General Heterocycle Chemistry Series, New York: Wilcy-Interscience. Safe, S.. and Hutzinger, O. (1973). Mass Spectrometry of Pesticides and Poliutants. Cleveland: CRC Press. Siuzdak, G. (1996). Mass Specirometry for Biotechnology. New York: Academic Press. Waller, G. R., Ed. (1972). Biochemical Applications of Mass Spectrometry. New York; Wiley-Intcrscience. Waller. R. and Dermer, O. €.. Eds. (1980). Biochemical Applicutions of Mass Spectrometry, Kirsl Suppl. Vol. New York: Wiley-Interscience. All spectra except the CI spectrum of Problem 2.9 were determined by El methods. 21 The exact mass of a compound determined by high-res- elution mass spectrometry is 2120833. What is the mo- Iecular formula of the compound? 2.2 The compound whose molecular formula is deduced in Problem 2.1 gives rise to the mass spectrum shown, De- duçe the structure of this compound. PROBLEM 2.2 100. so ao 105 60 BO 100 120 140 160 180 200 23 24 25 26 The mass spectrum of 2-butenal shows a peak at 247 69 that is 28,9% as intense as the base peak. Propose at least one fragmentation route to account for this peak, and explain why this fragment would be reasonably stable. 27 The mass spectrum of 3-butyn-2-ol shows the basc peak at m/z 55. Explain why the fragment giving rise to this peak would be very stable. 28 Consider thc mass spectra below of two isomers (A and B) of molecular formula CH. Determine their struc- tures and explain the major spectral features for each. The mass spectrum of o-nitrotoluene shows a substantial peak at m/z 120. Similar analysis of a,e,a-tri-deutero-o- PROBLEM 2.5, Isomer À. % of Base Pesk a Problems nitrotoluene does not give a peak at m/z 120 but rather at m/z 122. Explain. Determine the structure for the mass spectrum shown below. Below find mass spectra for compounds C-F. Compound Chasan M + 1 peak that is 2,5% of M (where M = 100%). Compound F can casily be converted to com- pounds D and E. Compounds C-E each give precipitates when treated with alcoholie silver nitrate, The precipitate ttom D is white, the other two are yellow. Deduce the structures of C-F. Isomer A Relativo Mass Spectral Data (Relativa Intansity) 1w 20 30 40 50 40 70 80 90 100 ma no no PROBLEM 2.5, Isomer B. % of Base Peak mz Bo 140 Intensity 21.9 2.4 134 135 150 160 90 180 Isomer B Relativo Mass Spectra! Data (Relative Intensity) 1 20 30 40 50 60 70 80 90 100 nO myz ro mjz 134 135 130 140 Intensity 30.4 34 150 160 70 180 42 Chapter? Mass Spectrametry PROBLEM 27. Mass Spectral Deta (Relative Intensity) s s % of Base Peak osB8588388 10 20 30 40 50 40 70 80 90 100 nO mjz PROBLEM 2.8, Compound C. 100 156 so 80 429 70 60 so 40 so 20 10 o % of Base Peak 127 40 60 80 100 120 140 mia (e) PROBLEM 2.8, Compound D. 9i 3888 0 so % of Base Peak 30 126 202 Relativa mfz intensity ns 57.7 no 42 120 2.6 140 150 160 70 180 PROBLEM 2.8, Compound E. % of Base Peak E) 4 60 80 100 120 140 160 Mass/Charge PROBLEM 2.8, Compound F, 79 100 108 90 so 7 8 e $ so mn 51 5% e 3 z so 10 65 o 0 70 80 90 0 mi Appendx A 45 Appendix A Formula Masses (FM) for Various Combinations of Carbon, Hydrogen, Nitrogen, and Oxygen" FM FM FM EM 2 HN, 32.0375 CHO 460419 CHINO 590246 c 12.0000 cHO 320262 47 CHAN: s9.0484 1 aa HNO, 47.0007 CHO, 59.0133 cu 130078 HO, 32.9976 cH.O, 470133 GHNO Sou 14 H;NO 334215 CHNO 470371 CGHN, 59.0610 N 140031 34 as CGH;O 59.0497 cH, 14.0157 HO. 340054 o, 47.9847 CHAN 59.0736 15 H.NO, 48.0085 eo HN 15.0109 380157 HN,O a8.0324 CHNO, 600085 ch; 150235 CHO, 48211 CHN,O 600324 16 390109 49 CHAN, 60.0563 o 15.9949 39.0235 HNO, 490164 CH.O, eo H;N 16.0187 s2 CNO 600450 Ci, 160313 40.0187 CH, 52033 CHN, 60.068% 1 400313 53 CHO 60.0575 HO 17.0027 a CSISN 53.0266 cs 60.0000 HN 17.0266 CHN, 410140 CHs 530391 61 18 CHAN 41.266 CHAO, 610164 HO 18.0106 CAs, 41,039 540218 CHN,O 61.042 24 42 SAO CHAN: 610641 Cc, 24.000 N; 420093 540344 HO, 61.0289 26 CNO 419980 CoHa Sa.0470 CHNO 610528 CN 26003] CHAN, 424018 55 2 CH, 260157 CALO 420106 CHN, 550297 CH, 62.0003 27 CHAN 42.034 CH 55.0184 CHNO, 620242 CHN 274109 CH. 420470 CHAN 5541422 CHN;O 620480 Cos 274235 as CH, 55.548 CHO, 62.0368 28 HN, 430170 56 63 N, 28.0062 CHNO 43.0058 CO s5.9898 HNO, 62.9956 co 27.9949 43.0297 CHNO 560136 CHNO, 630320 CILN 280187 a3.0184 GHN, 56.0375 4 Cs 280313 430422 GHO 560262 CH, 640313 430548 CHEN s6.0501 65 290140 44 CH, 56.0626 CHAN 65.0266 290027 NO 440011 57 CH. 65.0391 294266 co, 43.9898 CGHNO STMIS 66 29.0391 CHINO 440136 GHN, 570453 CHAN 66.034 CHAN, 440375 CH;O 5741340 CH, 66.0470 29.980 CALO 440262 CJHSN 57.0579 67 30.0218 CHAN 44.0501 CH, s7.UmS CHaN; 67.0297 300106 CaHg 440626 58 CALO 670184 300344 45 CHN;O 580167 CHEN 67.0422 30.0470 CH;NO as0215 CHN: SE.0406 CH, 67.0548 CHN, 450453 CALO, 58.0054 68 310058 CHO 45.0340 CHNO 580293 CHAN, 680375 3140297 GHN 450579 CHEN, 580532 CHO 68.0262 310184 CHO 580419 CHAN 68.0501 31.0422 45.9929 CHAN 580657 CoHs 681626 460054 Cata 580783 e 31,9898 CHANO 460293 s9 GHNO 690215 HNO 32.0136 CH; 460532 CHNO, S9A007 CHAN. 694453 «Nyilh permission ftom J.H, Beynon. Mass Speetrometry and its Application to Organic Chemistry, Amslerdam. 1960. The columns headed FM contain the formula masses based on Lhe exact mass ol lhe most abundant isotope of cach element; these masses are bascd on the most abundant isotope of carbon having a mass ví 12.0000. Note that the table includes only €, H, N, and O, 46 Chapter? Mass Spectrometry Appendix A (Continued) EM FM EM EM CHLO 69.340 CHINO, 764399 CHAN: 850767 GHNO, 900555 CHAN 69.0579 CHNO 760627 CHO 85.0653 CoHNO 900794 CH, 69.0705 CALO, 760524 CoHaN 850892 CHoO 900681 7” CHN 760187 Colts 851018 CAE, 900470 GHN, 70.0406 CH, 764313 ” CHO, TOND5A n 860116 CH;0, 91.0031 GHNO 700293 CHNO, TU!3 à 64355 910269 CN, 700532 CAIO: TIE CHAN, 860594 910508 CHAO 7.0419 CHINO, 770477 CJHLNO, 8640242 910746 GHN 70.0657 CH; 774891 CALMO 86480 91.0395 CH 700783 R CHAN; 864719 910634 n CHO. 780817 CH. 86.368 910422 CHNO TLNM6 CHAN 780344 C4HANO 860606 910548 CAIN, 710484 CH, 78.0470 CN, 860845 C;H.O, 710133 7” CHyO 860732 920109 CHNO TG CHAN 790422 CHyN 860970 920348 CH, 71.0610 CH, 79.0548 Cotia 86.1096 920586 CHROo 710497 so 920473 CHN 71.0736 CHAN, 80.0249 870672 92.0262 CHy 71.0861 CHAN, s0.0375 870082 920501 n CHLO 80.0262 870320 920626 CHLNO, 720085 CSHAN 80.0501 87.0559 CHNO 720324 CoHs 80.0526 NTUTOR 930187 CHAN, 720563 81 87.046 920426 CaHsO: nam CHAN; 81.0328 87.0684 930453 720449 CHEN, B10453 870923 930340 72.168K CHO 810340 7081 930579 72.0575 CSHN 810579 871049 93.0705 T2BI4 Cos 8LOTOS FENDA] s2 880273 940266 CHAN, 82.0406 88.051 940406 T3OLh4 CANO 820293 880750 940293 730402 CHAN, 820532 880160 940532 730641 ECHO 820419 88,0399 Sa. 0419 730289 C5HN 82.0657 B8.0637 940657 7a0528 CH 820783 8$.0876 940783 730767 B3 880524 730653 CHAN, 830484 88.0763 950484 730892 CALO, $.0133 88.3001 95.037] CHNO 83.037] BS.OBAS 950610 74003 CHAN, 83.0610 950497 74242 HO 83.0497 89.0351 950736 74 vago CHN 830736 89.0590 95.086] 744719 CH 83.086] 890820 740368 84 so.0238 960563 74.606 CHNs 840563 89.0477 960211 T4BAS CGHO: sat K9.0715 CHINO 960449 T4UT32 CHNO 840449 890954 CHAN. 96.0688 CAN, sa.0688 89.0603 CH, 9640575 750082 CHO 840575 89.084] CN 960814 7541320 CHAN 840814 89.039] CH; 960939 7541559 CH 84.0939 97 750798 85 CANO, 90019] CHN, 97OSIS 75.0446 CAHAN,O CHNO, 900429 CILNO 97UM 750684 CHAN. CHNO 900668 CALO; S7u289 CO» as.0289 CHNs 900% CHNO 970528 760160 CAHSNO 850528 ECHO, 900317 CSHSNs 970767 Appendix A (Continued) AppendixA 47 EM FM FM FM CHOo 970653 w2 105.0790 CoHeN, 1100594 970892 CHAO 1020542 105.453 CSHENDO TMAO4SO 971018 CANO, 1020191 105,0340 CHN, 1100719 CANO, 1020429 105.0579 CHO, 1100368 980355 CoHANGO 1020668 105.0705 CHNO 1100606 98.0594 CaaN, 1020907 CN, 1100845 98.242 CHO, 1020317 1060140 CH 00732 98.0480 CANO, 1020555 106.0379 CHoN 1100970 980719 CANO 1020794 4106.0617 CH 110.1096 984368 CN, 1021032 1060856 m 98,0606 CiHaO, 1020681 106.026 CAHNGO 111.043 98.0845 CHaNO 1020919 106.054 CHN, LOS 98.0732 CHuN, 1021158 106.0743 CHINO, 1110320 980970 CHaO 1021045 CHçO, 1060630 CHN,O 1110559 98.1096 CH 102.0470 CHINO 1064293 CHN5 110789 103 Coe 1060532 CO, 1110446 99.433 CH.NSO, 103.0382 CHO 1060419 CHNO 1110684 99.0672 CGHNO 103.0621 CELN 106.0657 CoHnN, 1110923 990082 CH;O, 1030031 CH 106.0783 CH O 1110810 990320 CAHNO, 1030269 CHaN 111049 99.0559 CAH;NO, 103.0508 1070218 Cais JILIITA 99.0798 CHN;O 1030746 107.0457 112 99.446 CHAN, 1030985 107.0695 CHN,O 1120586 99.0685 CaHLO, 1030395 10740344 CHN.O, 1120273 99.0923 CHNO, 1030634 CAHNO, 1070583 CHNO 12050 99.0810 CHNO 1030872 CHN, 1070484 CAHLN, 1120750 99.1049 CHaN, 10 GHNO 107030 CHO, 20160 991174 CHnO, 1030759 CAN, 1070610 CHNO, 1120299 CHNO 103.0998 CHO 107.0497 CHNO 1120637 CHN,O 1000386 GHN 103.0422 CHAN 107.0736 CHuN, 1120876 CALN;O, 1000273 CaH; 103.0548 CH 107.0861 CHLO, 1120524 CaHN;O 1000511 104 os CHeNO 11207%3 CHaNS 1000750 CHN.O, 1040222 CHAO, 10840297 ChHaN, 1121001 CHO, 1000160 CHN.O, 1040460 CHAO, 108.0535 CHoO 1120888 CAHNO, 100.0399 CoHaNGO 1040699 CHO, 1080422 CHAN IT CHEN;O 1000637 CHO, 040109 GELN, 1080437 CH, 112.1253 CoHeNs 1000876 GHNO, 104038 CJHN.O 1080324 3 CO, 1000524 CHNO, 1040586 CHN; 1080563 CHAN 1130464 CHoNO 1000763 CAELoN;O 1040825 CIO, 108021 CAHSN,O, 1130851 CH-N, 1001001 CoHaNs 1041063 CHENO 1084449 CHAO 1130590 CHoO 1000888 CHO, 1040473 CHAN, 1080688 CN, 1130829 CN 1001127 CNO; 1040712 CHO 108.0575 CHO, 1130238 CH 100.1253 CNO 1040950 CHoN 0SOBIA CHNO, 1130477 ni CHGO, 1040837 CH 108.0939 CALNO 1130715 CAHANO, 1010113 CHAN, 1040375 199 CoHaNs 1130954 101.0351 CHO 1040262 CHNO, 1090375 CO, 1130603 101.0590 CHAN 104,0501 CHEN, 1090515 CHANO 113084 101.0829 CiHa 104.0626 CHN;O 1090402 CMN, 131080 1010238 105 CN; 1090641 GHGO 113097 101.047 CHINO, 1050300 CHO, 1090289 CHAN 1131205 1010715 ChHGN5O, 1050539 CHNO 1090528 CH 113.1331 101.0954 CNO 1050777 CN, 1090767 14 1071.0603 CHO, 1050187 CHO 109.0653 CHNO 1140542 1OL0841 CHNO, 1050426 CHN 1090892 CHAO, 1140191 1011080 CANO, 1050664 Caia J09.1018 CHN,O. 1140429 101.0967 CHyN;O 105.0903 110 CNO 114.068 1011205 CHO, 1050552 CHAN 1100355 CN 1140907 50 Chapter? Mass Speetrometry Appendix A (Continued) FM EM FM EM 137.0238 CNO, 1400586 142.1233 CoHaN, 1440688 1370477 CALANSO 1400825 142, 1471 CHyO 1441515 1372.0715 CHoN, 1401063 1420532 CuthO 1440575 1370954 CHAO, 40473 142.1358 ColoN 1440814 1370603 CHNO, 1402 1421597 CH 144.0939 37.084] 1460.0950 142.0657 145 1371080 140.1189 142.1722 CHNO, 1450249 137.0967 140.0837 1420783 CH,N;O, 145.048 1371205 140.1076 CHN,O, 1450726 137.1331 140,1315 143.0093 CNO, 1450375 140,1202 143.033] C5Ho 40, 1450614 13841641 140.140 143.0570 CHyN;O, 1450852 1380304 140.0501 1430218 CHaN,O 145.109 138.0542 140.156 143.0457 CHO, 145.050] 138.019] 140.0626 t43,0695 CNO, 1450739 1380429 143.0934 CoHh;N,O, 1450978 V38.0668 1410175 CNO 145.1216 138.0907 141.0413 CHAN, 1451455 1384317 CAHLNO, 141.062 GHN, 1450515 138.0555 CALN;O; 1410300 CHO, 1450865 138.0794 CANSO, 1410539 1431298 CAELNO, 1451103 1238.1022 CHNO 141077 143.0708 CHN;O 1451342 138.0681 CHO, 1410187 143.0947 GHoN; 145.1580 1380919 CHNO, 1410426 143.185 CAHANGO 145002 138.115$ CANO, 410664 143.1424 GHN, 1450641 138. 1045 CAHN;O 1410903 143.1072 CHjO, 1451229 138.1284 CaHoN, t4L1142 1431311 CGHyNO 145.1467 138.1409 CO, 1410552 143.1549 CoH;NO 1450528 CHyNO. 141.0790 143.0610 CoHGNS 1450767 11390257 CALAN;O 1411029 143.1436 CuH5O 145.0653 CHNO, 1390144 CNA 1411267 143.1675 CoHyN 1450892 CAHNAOS 1390382 CHAO, 141096 143.0497 CuHa 14S.1OI8 CHENO 13920621 CHANO AL I154 143.0736 146 CANO, 1394269 CN, 1411393 143.0861 CaHANSO, 1460328 CHAN,O, 1390508 CO 141.1280 CHN,O, 1460566 CHNO 1390747 CN T4LISIO 1440171 CaHiN,O: 146.0805 CH, 1390985 CoaHN 410579 144.0410 146.0453 ECHO, 1390395 Cita 141.644 144.0648 146.0692 CALNO, 139.,0634 CaH; 141.0705 144.0297 146.0930 CANO 390872 142 144.0535 146.1169 CANSO 39 E CHNO, 1420253 1440774 146,0579 CHO, 1390759 CANO, 142049 144.1012 CHNO, 1460817 CHANO 1390998 CHNO, 1420140 1440422 CoHN,O, 146.1056 CHAN 1391236 CAHN,O, 1420379 144.066] CLANSO 146.1295 CANSO 1394297 CSHANSO, 142.0617 CHaN;O, 1440899 CHAN, 1460594 CHAO 381123 CHNSO 1420856 CAAN;O 144.1138 CGHO, 1460943 CH 1393.1362 CHO, 1420266 CoHuN, 1441377 CHNO, 146.1182 Coia 139.148 CANO, 1420504 CHoO, 1440786 CHuNO 146.1420 CH; 1390548 CHoNO, 1420743 GHANO. 144.1025 CO, 146.003 140 CoHoNGO 1420981 CHN;O 1441264 CAHENSO 1460480 GHN,O, 1400335 CoHaNs 1421220 CHAN, 1441502 CoHaN; 1460719 CJLN,O, 1400222 CHO, 1420630 CHN, 1440563 CoHaO, 146.1307 CHN.O. 1400460 CHaNO, 1420868 CALO, 1441151 CGHO, 1460368 CANO 140.0699 CHuN,O 142.107 CH NO 144.1389 CHNO 146.0606 CHO, 140009 142.1346 Ca, 1441628 CHN, 1460845 CHAO, 1400348 142.0994 CHAO 1440449 CoHiO 1460732 Appendix A (Continued) AppendixAa 51 FM FM FM FM CoaN 1460970 CHuN;O, 149.1165 CHNO 1510998 CNO 1540856 Cuisa 146.1096 CHN,O 149.064 CN, 1511236 CO, 1540266 147 CO, 1490814 CollsO ISLILZ3 CH;NO, 1540504 CNO, 1470406 CHNO, 149.1052 CoHaN 1511362 CHaN;O, 1544743 CaHyN5O, 1470644 CHNO, 1490351 CuHjo 1511488 CGHoN;O 1540981 CHnN,O, 1470883 CHN;O 1490590 152 CHaN, 154.120 CHNO, 1470532 CHAN, 1490829 CHN,O, 152.0797 CO, 154.0630 CHN;O, 1470770 CHO, 1490238 CNO, 1520335 CH;NO, 1540868 C5HaN;O, 1471009 CHNO, 1490477 CALN;O, 1520222 CoHN;O 154/1107 CHNO 1471247 CHGN;O 1490715 CHENSO, 1520460 CN, 1541346 CHO, 1470657 CN; 1490954 CHNO 15210699 CHuO, 1540994 CHNO, 1147.0896 CHO, 1490603 CGH;NO, 1520348 CHENO 1541233 CNO, 1471134 CHANO 1490841 CHNO, 1520586 CoHheN, 1541471 CHyNO 1471373 CoHoN, 149.1080 CHyN;O 1520825 CoHsO 1541358 CHNO 1470433 CusO 1490967 CHoN, 1521063 CiolyN 1541597 CHN, 1470672 CotlsN 149.1205 CHO, 1520473 CHEN 1540657 CHsO, 147102 Cut 149.1331 CoHyNO, 1520712 Cia 154,1722 CHANO, 147.1260 150 CAH,aNDO 152.0950 Colo 154.0783 CANO, 1470320 CoHiN4Os 150.0641 CaHuN, 1521189 155 CAHGN;O 1470559 CHNGOs 1500879 GHoO, 1520837 CHN,O, 1550093 CN, 1470798 CHAN, 1504118 CHuNO 152107%6 CSH:NGO, 1550331 CHO, 1470446 CH5NO, 1500766 CN, 1521315 CH;N,O. 1550570 CHLNO — 147.0684 CNO; 150.1005 CO 1521202 CAHNO, 1550218 CHN, 1470923 CAHAN;O, 1150.0304 CoHhaN 1521440 CH;N;O; 1550457 CoHuO 1470810 CHN,O 1500542 CaHN 1520501 CHNGO, 155.0695 CoHaN 1471049 CHO, 1500892 CH 152.156 CNO 1550934 ChHhis 1471174 CHN,O, 150.0429 Coy 152.0626 CHO, 1550344 “8 CHAN, 150.0668 153 C)H;NO, 1550583 CAHAN.O, 1480484 CHoNs 1500907 CHN;O, 1530175 CHN,O, 1550821 CHyN;O, 1480723 CH, 1500317 CHSNSO, 1530413 CHN;O 155.1060 CHN,O, 1480961 CNO, 1500555 CHNO; 1530300 C HO, 1550708 CHoNO, 1480610 CoHoN,O 1450.0794 CHN;O, 1530539 CHaNO, 1550947 CNO; 1480849 CoHN; 1501082 CHN,O 153077 CAoN;O 155.1185 CHN;O 148.1325 CO, 1500681 CHO, 1530187 CH, 1551424 CHN,O 1480386 CHNO 1500919 CHNO, 1530426 CHsO, 1556.1072 CO, 1480735 CHN, 1501158 153.0664 CHo5NO 1551314 CHNO, 1480974 CoHuO 1501045 153.0903 CHuN, 1551549 CH NO, 1481213 CoHN 1501284 153.1142 CoHbN, 1550610 CHN;O 1480511 ChH:s 150.1409 153.0552 CoHçO 1551436 CHAN, 1480750 151 153.0790 CoHaN 155.1675 CHO, 1481100 CH NO, 1510719 CHN,O 1531029 CuH;O 1550497 CHENO, 1480399 CNO, 1510958 CoHisN, 1531267 CuHN 1550736 CANO 148.0637 CHNO, 1510257 CH5O, 1530916 Calha 155.1801 CaHoN, 148.0876 CNO, 151.0845 CHNO 1531154 CoHy 1550861 CO, 1480524 CHN;O, 1510144 CHyN, 1531393 156 CHNO 1480763 CHN,O, 1510382 CilO 1531280 CHAN,O, 1560171 CN, 1481001 CANO 151.062] CoHoN 1531519 CHN5O, 1560410 CoHoO 1480888 CH.NO, 151.0269 CaHN CSHANSO, 1560648 CoaN 1481127 CHN,O, 1510508 CiHo CHNO, 1560297 CuHi 148.1253 CHNO 151.0746 CoH, CHN,O, 1560535 149 ChHaN, 1510985 154 CHoN;O, 1560774 CHN;O, 1490563 CHO, 1510395 CHN;O, 1540253 CHaN4O 1561012 CHyNO; 149.080] CHNO, 1510634 CHEN, 1540491 CHO, 1560422 CHN,O, 149.1040 CNO 1510872 CHNO, 1540140 CHNO, 156.0661 CHNO, 1490688 CHaN; ISLA CSHGNSO, 1540379 CHaN,O, 1560899 CiHnN;O, 1490927 CH O, 1510759 CHsN;O, 1540617 CHuN;O 156.138 52 Chapter? Mass Spectrometry Appendix A (Continued) FM FM FM FM CHeN, 1561377 CHuN:O, 158.1056 CHuNO, 1600974 CoHoNa 162.0907 CH;O, 1560786 CyHNSO 158.1205 CHN;O: 1601213 CoHyO, 1621256 CAHNO, 156.1025 CoHasN, 158.1533 CHN,O 1601451 CH, 1620317 CoHeNGO 156.1264 CN. 158059 CN, 160.1690 CH;NO, 1620555 Casa; 1561502 CO, 1580943 CANO 160.051] CHN,O 162.079 CHN, 1560563 CH$NO, 1581182 CN, 1600750 CHoN, 1621032 CH5O, 1561151 CoHis GO 158.1420 CHO, 1160.1100 CotoO, — 162.0681 CHNO 156.1389 CoHoN, 158.1659 CAHNO, 160.1338 CoHaNO 1620919 CoHaoN, 156.1628 CHN,O 1580480 160.1577 ColuN, 1621158 CoHeNO 156.0449 CoHaN, 1580719 160.0399 CoH4O 1621045 CiokN, 156.068 CHO, 158.1307 1600637 CoHN 1621284 CoHyO 1561515 CHNO 158.1546 160.0876 Cole 162.1409 CoH:N 1561753 CoHO, 1580368 160.1464 163 ChHO 1560575 CoHNO 1580606 160.0524 CH,N;O, 1630719 CaHoN 1560814 CoHuN, 1580845 160.0763 CH NO, 1630958 CH 156.1879 CotizO 1581672 160.1001 C5HsN5O, 163.1196 Co 156.0939 CoHgO 1580732 160.0888 CHaNO, 1630845 157 CoHoN 1580970 160.1127 CALANGO, 1631083 CHNO, 1570249 CoHis 158.1096 160.1253 163,1322 CH;NAO, 1570488 159 163.0382 CHN,O, 1570726 CH;N;O, 1590406 161.0563 1632.0621 CAHNO, 1570375 CHNO, 1590644 161.0801 a 1630970 CHNO, 1570614 CHN,O, 159.0883 1614.1040 CH5NO, 1631209 CHN;O, 1570852 CHNO, 1590532 2H NO, 161.068 CHHNO, 1630269 CHoNO 157108 CHNO, 159.070 CNO; 1610927 CH;N;O, 1630508 CHO, 1570501 CHoN;O, 159.109 CHN;0, 161.1165 CHAO 163.0746 CHyNO, 1570739 CNO 159.1247 CH5NO 161.1404 CHN, 1630085 CHN,O, 157098 CHnO, 1590657 CHNO 1610464 CHO, 163035 CHaN;O 157.1216 CHaNO, 1590896 CSAHEN;O, 1610351 CHNO, 1630634 CHyN, 1571455 CHN,O, 159.1134 CH;N;O 1610590 CHnN,O 1630872 CAN, 1570515 CHGN;O 159.1373 CAHN, 1610829 CN; 163 CO, 1570865 CHN,O 159.0433 CH5O, 16L1178 CaHO, 1630759 CANO, 1571103 CHAN, 159.0672 CAH9NO, 1611416 CoHNO 1630998 CAHN;O 157.1342 CHO, 1591021 CHO, 1610238 CoHN, 163.1236 CHyN; 157.1580 CHG5NO, 159.1260 CH;NO, 1610477 1H5O 1631123 CHNO 1570402 CAHN,O 159.1498 CHN;O 1610715 CaHN 1631362 CN; 1570641 CoNo 1591737 CoHoN, 1610954 CoHio 163.1488 CO, 157.1229 CHNO, 159.0320 CoHO, 1610603 164 CHNO 157.1467 CH;N;O 1590559 CoHNO 161.084 CHN,O, 1640797 CoHaiN, 157.176 CHAN, 1590798 CoHssN> 161.1080 CsHN;O, 164.1036 CoHiNO 1570528 CHyO, 159.1385 ChHjO 1610967 CH Ns, 164.1275 CoHsNo 1570767 CHNO 159.1624 ChHN 1611205 CHN,O, 1640235 CoHyO 1571593 CoHjO, 1590446 CoHy 161.1331 CH,NO, 1640923 CoblN 1571832 CiHoNO 1590684 162 CH N;O, 1641162 ChHGO 1570653 CiiNo 1590923 C5HyoN,O, 1620641 CHN;O, 1640960 CaHN 1570892 CaH4O 1590810 CHN;O, 1620879 CHANO 1640699 Cos 157.1018 CaHoN 1591049 CHNO, 1621118 GHO, 164.1049 158 CoHis 1591174 CHoNO, 1620766 CHNO, 1640348 CHN;O, 1580328 160 CHN,O, 162.105 CaHNGO, 164.0586 CHNO, 158.056 CHN,O, 1600484 CHN;0, 162.124 CAHoN;O 1640825 CoHioN AO, 1580805 CoHyoN;O; 1600723 CHaNO 1621482 HoNo 1641063 CAHANO, 1158.0453 CHN4O, 160.096] CHEN 1620542 CHO, 164 CHN:O, 1580692 CHyNO, 1600610 CHaO, 1620892 CHANO, 1640712 CHoN;O, 1580930 CHoN,O, 1600848 CHENO, 1621131 CHoN;O 1640950 CHuN,O 1581169 CHuNsO, 160.1087 CH,N50, 162.1369 CHuN, 1641189 CH oO, 1580579 CHNSO 160.1325 CAHGN;O, 1620429 CoHoO, 1640837 CHNO, 1580817 CHO, 1600735 CHEN; 1620668 CoHuNO 1641076 Appendix A (Continued) AppendixA 55 FM FM FM CiHe 180.0939 182.0970 184.1702 CoHN;O 1860668 181 182.2036 184.1941 CioHhoNa 18640907 CHNO, 1810249 182.1096 1840524 CuH4Os 186.1256 CHNO, 181.0488 184.0763 CuHyNO, 186.1495 CHN,O, 181.0726 183.0406 184,1001 CobLaN;O 1865.1733 CHANO, 18140375 1832.0644 184.1828 CoHaN, 1861972 CHNO, 1810614 CHANO, 1830883 1842067 CoHaNO, 18640555 CHN;O, 1810852 C,HANO, 1183.0532 CoH5O 1840888 CoHoNhO 186.0794 CNO 18LIO9L CaHuNHOs 1830770 CoHyN 1841127 CaHoN; 186.1032 CHO, 1810501 CoHN;O, 183.1009 [o 1842192 Cullo0: — 186.1620 CHNO, 1810739 CHNO 183.1247 CuHhs 1841253 C)HaNO 1861859 CALAN,O, 181.0978 CHyO, 1830657 185 CoHaNo 1862098 CH NO 1811216 CH,NO, 183.089 CHN;O, 1850563 Co: 186.068] CoHaNs A8I.1455 CHN5O, 183.134 CHuN;O; 185.0801 CoHaNO 1860919 CiH5O, 1814865 CHGN5O 183,1373 CHN,O, 185.1040 CoHuN, 1861158 CuHiNO, 1811103 CoHyN; 1831611 CHNO, 1850688 CoH,O 1861985 CoHaN5O 181.1342 CoHN; 1830672 Co NHO; 1850927 CoHl4O 1861045 CiHiN, 1811580 CoHisOs 183.1021 CoH,sN5O, 185,1165 CilleN 186.1284 ChH;N; 1810641 CoHNO, 183.1260 CHN,O 1851404 Coths 186.1409 CaHO, 181.129 CitloN;O 183.1498 CH5O, 1850814 187 CuHLoNO 181.1467 CoHaN, 1831737 CoHNO, 1185.1052 CHyNO, 1870719 CoHaN> I8LITO6 ChHGN,O 18300559 CHL;NiO, 185.129 CHyN;Os 1870958 CoHhNO 1810528 CaHN; 1830798 CALNSO 185.1529 CHANO, 1871196 CoH5N, 1810767 CuHsO, 1831385 CHaN, 1851768 CHnNO, 1870845 CoHyO 1811593 C..HyNO 183.1624 CoH;N5O 1850590 CNO, 187.1083 CoHaN 1811832 CuHaN, 1831863 CoHN, 1850829 CAL:N;O, 1871322 CoHO 1810653 CoHO, 183.0446 CoHrOs 1851178 CH NO 1871560 CoHaN 181.082 CoHoNO 1830684 CoElaNO, CHNO 1870621 Cola 181,1957 CoHnN, 1830923 CoH,iN5O GHO, 1870970 Cuba 18L1018 CoHaO 1831750 CioHaN5 CHNO, 187.1209 182 CoHasN 1831088 Ca toN,O CNO, 187.1447 CHN,;O, 1820328 CoHHO 1830810 ChHnN: CHN;O 1871686 CHAO, 1820566 CoHN 183/1049 CuHyO, 1851542 CoHaN, 3871925 CHwN.O, 1820805 CaHhs 1832114 CuHaNO 185.178 CuH;N,0, 18740508 CANO, 1820453 CuHs 1831174 Cubos, 1852019 CuHyN;O 1870746 CNO, 1820692 184 CaHO, 1850603 ColhiN, 1870985 CALAN;O, 1820930 CHN,O, 1840484 CoH)NO 1850841 CO 18713 CALANÇO 182.1169 CHoN5Os 1840723 CoHN, 185.1080 CaHaNO, 1871573 CHO, 1820579 CHoN,O, 1840961 CoHxO 185.1906 CoHoN;O 1871811 GHoNO, 1820817 CANO, 184.0610 CoHaN 1852145 CoHosNs 1872050 CH NO, 182.1056 CaHN,O, 1840848 CoHO 1850967 ChlhO, 1870395 CALÇNHO 182.1295 CoH NO, 184.1087 CoHN 185.1205 ChH,NO, 1870634 ColloNa 1821533 CoHN4O 184.1325 CuHir 185.1331 ChHN,O 1870872 CotN, 1820594 CH5O, 1840735 186 CoHoNs ISA CoHuOs 1820943 CH,NO, 1840974 CH NO, 186.064] ChHO, 1871699 CoHNO, 182.1182 CH NO, 1841213 CHAN,O, 186.0879 CaHNO 187.1937 CH NO 182.1420 CHaN;O 1841451 CHuN,O, 186.118 CoHhO, 1870759 CioHaN5 182.1659 CoHaoNs 1841690 CHaNO, 1860766 CaHNO 187.0998 CHAN; 1820719 CoHN;O 18400511 CANO; 186.105 CotheN, 1871236 CuHO, 1821307 CoHN, 1840750 CAH NO, 186.124 CaHçO 1871123 ChHy)NO 182.1546 CoHOs 1841100 CHuNO 186.1482 CaHoN 1871362 CBoN, 1821784 CoHhsNO, 1841338 CHNO 18640542 Cialis 187.1488 CoHANO 1820606 CoHaNhO 184.157 CH,O, 1860892 188 CotloN, 1820845 CoHmN, 1841815 CHNO, 186.113] CHoNO, 1880797 CoHyO 1821671 CoHaN;O 1840637 CoH,aN;O, 186.1369 CHN;O; 188.1036 CeHaN 1821910 Cu, 1840876 CoHoNiO 186.1608 CHyNO: 188.1275 CoHyO 1820732 CiHO, 1841464 CoHoN20» 186.0429 CANO, 1880923 56 Chapter? Mass Spectrometry Appendix A (Continued) FM EM FM F CHN:O, 188.1162 190 CLHN 1910736 CaHaO 1931593 HN;O, 188.1400 CHaNZOs T9UA954 Cut 191.1801 CaHaN 1931832 CNO 1881639 CHeN5O, 1901193 CH 1910861 CuO 1930653 CHHAN,O, 1880460 CoHaNGO, 190.1431 192 CoHaN 1930892 CANSO IBR06SS CHINO, 1900491 CHN,O, 1921111 CuHys 193.1957 CHO, 188.1049 CHINO, 190.1080 CoHyaN;Os 1921349 CiHya 193.1018 CHaNO, 188.1287 CHLaNÇOs 190.318 CNO, 1921588 194 CNO, 188.1526 CoHNs5O, 190,1557 CHN;O, 1920410 CNO, 194.1267 CHaN;O 1881764 CoHoN,O 1901795 CANO, 192.0648 CHNO, 1940328 CotlaNa 1882003 CoHGNAO, 1900617 CHNO, 192.123 CaHaN;Os 1940566 Cut N;O, 1880586 CH NO 1900856 CHyN,Os 1921475 CH Ns, 1940805 Cio 188.0825 CHaO, 1901205 CHNO, 1920297 CHNO, 1940453 CotaNs 188.1063 CoHyNO, 190.1444 CoHN,O, 1920535 CALONIOs 1940692 CoHyO, 1881413 CHINO, 190.162 CoHoN;0: 192.0774 CoLoN;O, 1940930 CoHNO, 188.1651 CoHaNO, 190504 CNO 192.1012 CHuNO 194.1169 CoHNDO 188.1890 CoHN5O: 1900743 CHyO, 192.1362 CoHO, 1940579 CuHO, 1880473 CoHaN5O 1900981 CulhO, 1920422 ChHNOs 1940817 ChELaNO, 1880712 CoHaNs 190.120 CiHNOs 192.0661 CuHNsO, 194.1056 CHN,O 188,0950 Co, 190.1569 CyaN;O, 1972.0899 CaHyoN5O 194.1295 CoHN, 1881189 C HO, 1900630 CoHNSO 1921138 CoHaNa 1941533 CuHsO, 1881777 C-HNO, 1900868 CoHNa 192.1377 ChHOs 1940943 CoH5O, 1880837 CoHNSO 1901107 CO, 1920786 ChHNO, 1941182 CoHLANO 1881076 CoHiNs 1901346 CuHNO, 192.1025 CH,aN:O 194.1420 CoHiN, 188.13]5 CoH4O: 1900994 CoHN,O 192.1264 CuBoN; 194.1659 CatlO 1881202 CoHNO 190.1233 CotlaNs 1921502 CoHoN; 1940719 CoHaN 188.1440 CaH 190.1471 CoHO, 1921151 CoHaO, 194.1307 Cotas; 188.156 c 190,1358 CoHaNO 192.1389 ColLoNO 194.1546 189 c 190,1597 CrHaN, 192.1628 1941784 CHAN;O, 1890876 c 190.1722 CoHAN, 1920688 194.0606 CNO, 1891114 e 190.0783 CALO ISASIS 194.0845 CHGN,O: 1891353 191 CoHoN 1921753 194.1671 CHNO, 189.1001 CH,sNGO, 191.1032 CoHeoN 1920814 CoHaN 1941910 HN,O, 189.1240 CHLGN;O: 1911271 eos 192.1879 1940732 HN;O, 189.1478 CNO, 1911509 CoHo 192.0939 194.0970 CHaNO 1894717 CENSO, 1910570 193 1942036 CoHNO, 1890539 C4HGNO, 1911158 CHN,0, 1931189 194.1096 GHN,O 1890777 CoHNGO, 1911396 CHyN;O, 1931427 GH50, 1891127 CdLiN;O, 1911635 CHINO; 193.0488 CH;N;O, 1950406 CHNO, 189.1365 CHN,O, 1910457 CHN,O, 1930726 CHN;O, 1954644 CNO, 189.1604 CoHoNO, 1910695 CHNO, 1931315 CHANO, CHaN;O 189.1842 CHuNO 1910934 CH:NO, 1930375 GHNO, 1950532 CuHjNO; 189.0426 CHO, 1911284 CAHGNIO, 1930614 CHyN;Os 1950770 CoHoN,O, 189.0664 CH NO, 1911522 CoH NO, 193.0852 CH ,N;0, 195.1009 CoHNSO 189.0903 ColhO, 1910344 CHaNO 193.109 CHANÇO 1951247 CioHaNa 189142 CoHNO, 1910583 CoH5O, 1930501 ColO, 1950657 CotlO; 189149] CoHy NO, 1910821 CoHNO; 1930739 CoHNO, 1950896 CoHaNO, 1891730 CoHNGO 1911060 CoHiaN,O, 1930978 CoHisN20» 1951134 CaH5O, 1890552 CiotlaNa 191.1298 CoHN5O 1931216 195.1373 CH NO, 1890790 CiHO, 19.078 CoHaN, 1931455 195.161 CoHNDO 189.1029 CUHANO, 190847 CuHnOs 1930865 : 195.0672 CoHNs 1890.1267 CHN;O 191185 CuHNO, 1931103 ChhaO, 195.102] CothaO, 189096 CoHoN, 1911424 CoHGN,O 193.1342 CiHaNO, 195.1260 CoHNO 8954 CoHO, 1911072 CuHhoN; 1931580 195.1498 CoHN, 189.1393 CoHoNO J9LI3L CoHO, 1931229 195.1737 Co 1891280 ColluN, 19LIS4Y CoHANO 1931467 195.0559 CoHoN 1891519 CoHoO 191436 CoHaN, 1931706 CoHoN; 1950798 Culto 189.1644 CoaN 1911675 CoHoNs 1930767 CoHO, 1951385 Appendix A (Continued) AppendixA 57 EM FM EM EM CoHyNO 195.1624 ChHhOs 1971178 CoHsN,O: 199.1083 CoHaN, 2002254 CoMoNo 1951863 CuHNO, 197.1416 CHN;O, 199.132 CiHO: 2000837 CAHNO 1950684 CuHaN,O 197.1655 CHN;O 1991560 CoHNO 200.1076 CoHaNo 1950923 CuHaN, 1971894 CotNO 199.0621 CoHN, 2001315 CoHO 195.1750 CoHNO 1970715 CoHsO, 1990970 CoHsO 2002141 CoHosN 195.198 CoHN, 1970954 CoHNO; 1991209 CuHçO 201 CuHnO 1950810 CoHnO, 1971542 CioHyoN,0, 199.1447 CuHaN 2001440 CoHloN 195.1049 CoHaNO 1971781 CoHyN;O 199.1686 CisHho 2001566 Cu 1952114 CoHasN, 1972019 CoHyoN, 1991925 203 CisHhs 195.1174 CoHO, 1970603 ChHHN;O, 199.0508 CH N,0, 2010876 196 CaHNO 1970841 ChHGN;O 1990746 CHysN;O; 201114 CHNO, 1964484 CoHN, 1971080 CuHhN, 1990985 CAHN,O, 2011353 CAHoN;O, 1960723 CaHsO 1971906 CuHçO, 199.1334 CH, NO, 201.101 CNO, 1960961 CoHN 1972145 CuHaNO, 199.1573 CHN,Os 201.1240 CHaNO, 1960610 CuHoO 197097 CoHoN,O 199.181 CoHN;O: 2014.1478 CHaN;O, 1960848 CaHiN 1971205 ChHosNs 1992050 CHN,O 2011717 CHNO, 196.1087 CiaHlos 197.2270 CoHNO, 199.0634 CoH,N;O: 201.0539 CoLN4O 196.1325 CisHy 1971331 CoHN,O 1990872 CaHGN4O 2010777 CoHrO, 1960735 198 CoHoN; 199111 CoHrOs 2011127 CoHuNO, 1960974 CoHuN,Os 198.0641 CrllsO, 199.169 CoHoNOs 201.1365 CioHisN,0, 196.1213 CHoN;O, 1980879 CoHNO 1991937 CH N,0, 201.1604 CioHaN5O 196.1451 CH NO, 198.8 CoHyN, 1992176 CoHNiO 201.1842 CiotlyNa 1965.1690 CNO, 198.076 CoHiO, 1990759 Cota, 2012081 CaHaN, 1960750 CHN,O; 198.105 CoHNO 1990998 CuH;NO, 2010426 CuH,Os 196.1100 CH NO, 198.124 CothsN, 199.1236 ChHN,O, 2010654 CaHNO, 196.1338 CoHNGO 198.1482 CoHO 1992063 CuHNsO 201.0903 CoHyN4O 196.157 CrotluOs 1980892 CoHoN 1992301 CuHeN, 201142 CuHoN; 1961815 CotiNO; 198.1131 CuHisO 1991123 CBO, 201.149 CoHaN;O 196.0637 CinHaN20, 198.1369 CaHoN 1991362 CHaNO, 2011730 CoHyNs 1960876 CooHoNsO 198.1608 CisHhy 199,1488 ChHosN,O 201.1968 CoHuO: — 196.1464 CoH»N. 198.1846 200 CuHaN, 2012207 CoHyNO 1961702 CuHN;O 1980668 CoHaN,O 2000797 CoH,O, 2010552 CoHaNo 196.1941 CnHioNa 198.0907 CaHN;Os 200.1036 CoHnNO, 201/0790 CoHO, 1960524 CiHO, 1981256 CoHheN,O, 200.1275 CoHN:O 201.1029 CoHNO 1960763 CuHaNO, 198.1495 CoHNO, 200.0923 CoHosNa 2011267 CoHoN, 196.101 CuHoN,O 1981733 CH,eN;O, 200.162 CoHxO, 2011855 CoHO 1960.1828 CMN; 1981972 CoH NO, 200.140 CoHyNO 2091.2094 CoHN 1962067 CaHNO, 1980555 CoHoNGO 200.1639 CoHnO, 2010916 CuHrO 1960888 CoHN;O 198.0794 CoHN,O 200.0699 CoHNO 2011154 CoHaN 1961127 CoHN, 198.1032 CilleO, — 200.1049 CoaHN, 2011393 CraFog 1962192 CoH»O, 1981620 CiHlyNOs 200.1287 CuHO 2011280 CiHio 196.1253 CaHyNO 1981859 CioHanN,O, 200.1526 CuHyN 2011519 197 ColeNo 1982098 CiHaN5O 200.1764 CosHy 201.164 CNO, 197.0563 ChHO, 1980681 CoHaN, 200.203 u2 CoHN;Os 19780801 CoHGNO 1980919 CoHN;O, 2000586 ChsN,O, 202.0954 CHoNsO, 1971040 CoHaN, 1981158 CuHoN;O 200.0825 CANSO; 202.1193 CHNO, 1970688 CoHyçO 1981985 CuHoN, 21063 CoHaN;O, 2021431 CHaN;O, 1970927 CoHoN 1982223 CoHaO, 2001413 CoH$N,O, 2020491 CoHisNO, 197.1165 CuHO 1981045 CHNO, 200.1651 CHeNO, 2021080 CHiNO 1971404 CoHiN 1981284 CHAN 2080.1890 CoH,N4Os 202.1318 Coltli0, 1970814 Cio 198,2349 CNN, 2002129 CoHN;O, 202.1557 CoHNO, 1971052 Cotia 198.1409 CoHGO, 2000473 CBoNGO UIT Cio,» 197.1291 199 CoaHaNO, 2000712 CiHGN;O, 2020617 CroHoNAO 197.1529 CHN;O, 1990719 CHyN,O 2000950 CooiN,O 2020856 CoHaN, 1971768 CAH,NGOs 19941958 CoHuNs 2001189 CuaOs 2021205 CaHN;O 1970590 CALSNO, 199.1196 CoHaO, 2001777 CiHaNO, 202.1444 CuHoN, 197.0829 CHaNO, 1990845 CaHhgNO 2002015 CuHaNO, 202/1682 60 Chaprer2 Mass Speetrometry Appendix A (Continued) FM FM FM EM CoHiNO, 215.0947 CuH,NO, 2170375 CuHoN, 2181784 ChEhoNAO 220.1325 CoHiN,O 215.1185 CuHN,O, 2170614 CioHoN, 218.0845 CoHO, 2200735 CoHNs 2151424 CuHNs0, 2170852 CeHoO 218161 CaHNO, 2200974 CuHisO, 2151072 CHAO 217.108 CisHaN 2IBAVIO CoHiN,0, 2201213 CuHyNO 215.131 ChHyO, 2147.1440 CoHoO 2180732 CoH,N;O 220.1451 CuHioN, 215.1549 CHINO, 2171679 CoHoN 2180970 CilloNa 2201690 CoHoO 215.1436 » 21TI9LT CiHos 218.2036 CaHNs 2200750 CoHyN 215.1675 2172156 CoHu 218.1096 CaHiOs 2201100 CiHos 2151801 2170541 219 CoHjsNO, 220.1338 216 2170739 CH,N,O, 219.1345 CaHyoN;O 2201577 CNO, 21614111 Co H,aN,O, 2170978 CHyN;0; 219.1584 CoHoN, 2201815 CoHN;Os 216.1349 CoHaNGO 2171216 CoHsN4O, 219.182 CuHoN; 2200876 CH,N,O, 216.158 CoHoN, 271455 CoH:N;O, 2190406 CuHyO, 2201464 CoHaN,O; 2160648 CoH,O, 2171804 CoHoN;Os 219.064 CalhaNO 2201702 CoHaNO, 216.1236 CrHyNO, 2172043 CroHlnNsO, 219.083 CuHaN, 2201941 CoHaN-O; 216.1475 CoHiO; 2170865 1H NO, 219.1471 CHiNO 2200763 CoHN50, 2161713 CHaNO, 217.1103 CiotosN;Os 2191710 CisHaN, 2201001 CiHaN;O 216.1952 CaHN,O 2171342 CioHosN40, 219.1948 CoHy4O 220.1828 CnHN,;Os 2160535 CoHhoN, 217.1580 CiHGNO, 2190532 CaHaN 220.2067 ChHhoN;O, 2160774 CaHO, 2171229 CoHaN;Os 219.0770 CoHoO 2200888 CHHoN,O 216.1012 CuHyNO 217.1467 ChHiaNsO, 219.1009 CiHuN 2201127 CaHyO, 2161362 CuHaN, 2171706 CoHNO 219.1247 Colli 2202192 CuHNO, 216.1600 CiHN, 2170767 CuHaO, 219.1597 CoHis 220,1253 CnH,N,O; 216.1839 CoHyO 2171593 CnHosNO; 219.1835 221 ChHN;O 2162077 CH 2171832 CoHnO, 2190657 CoHaN;O, 221.1502 CuHaN. 2162316 CoHaN 217089 CoHyNO; 219.0896 CHN;O, 221.1741 CoHkO, 2160422 CioHos 217.1957 CoHN,0, 219.1134 CioloN;O, 2210563 CoHuNO, 2160661 CoHis 217.1018 CrHyNSO 219.1373 CioHuN;O, 2210801 CoHN,O; 2160899 218 CoHoN, 219.161 CioHN4O, 221.1040 CoHN;O 2161138 CoHyaN,O, 218.1267 CoHO; 2191021 CiHaNO, 221.1628 CoHyN, 216137 CHNiO, 218.1506 CaHNO, 219.1260 ChHnNO, 2210688 CoHiO, 2161726 CHoN,O, MBITA CiHN,O 219.1498 ChHyN,O; 2210927 CoHiNO, 216.1965 CoHN5O, 218.056 219.1737 Co H,sN;0, 221.1165 CoHN;O 2162203 CioHloN4O, 218.0805 219.0798 CoHyN,O 221.1404 CaH5O: 2160786 CoHyNO, 218.1393 219,1385 CoHsO, 2210814 CaHuNO, 216.1025 CioHaN>0, 218.1631 219,1624 CH,NO; 2211052 CaHiN,O 216.1264 CioHaNG0; 218.1870 219.1863 CoH,/N;O, 221.1291 CotlNs 216.1502 CioHaeN4O 2182108 219.0684 CoHyN;O 221.1529 CoHygO, 2162090 ChH,NO, 2180453 219.0923 CoHaN, 2211768 CuHO, 2161151 CHoN>O, 218.0692 2191750 CaHoN, 2210829 CuHaNO 216.1389 CNO; 218.0930 219.1988 CoHO, 22111798 CuHyN, 2161628 ChHaN4O 2181169 219.0810 CoHyNO, 221.1416 CyHyO — 216.1515 ChHyO, 2181518 219.1049 CiaHyN:O 2211655 CaHaN 2161753 ChHNO, 2181757 219.2114 CoHaNs 2211894 CoHoN 2160814 ChHN,0, 218.196 219.1174 CuHoNO 2210715 Cita 216.1879 CoHO, 2180579 CuHaN; 2210954 CoHo 2160939 CoHrNO; 2180817 CHyN;O, 220.1424 CuHyO, 2211542 217 Co HuN5O, 218.1056 CHN;O; 220.1662 CuHNO 2211781 CHrN,O, 217.1189 CoHN5O 218.1295 CHN,O, 220.1901 CuHosN, 2212019 CHN;O; 217.1427 CBN, 2181533 CoHN,O, 220.0484 CsH,O, 2210603 CHaN,O, 217.166 CoHO, 218.183 CrHoN;O; 220.0723 CaHyiNO 2210841 CoHN;O, 2170488 CoHuO: 2180943 CiHaN4O» 220.0961 CisHoN, 2211080 CoHN,O, 2170726 CoHaNO, 218.1182 CoHaNO, 220/1549 CsHsO 2211906 CoHyNO, 2171315 CaH,aN,O 218.1420 CiHyNiOs 220.178 CsHoN 2212145 Cita N,O, 217.1553 CoHN, 218.1659 CHINO, 2200610 CoH5O 2210967 CioHoN5O» 217.1791 CuH,aO, 218.1307 CnHaN;O; 220.0848 CoHaN 2211205 CioHasN4O 217,2030 CoHyNO 2181546 CuHN;0, 220.1087 Cit 221.2270 Appendix A (Continued) AppendixA 61 FM EM FM Colo 221.1334 CuHNO, 2230634 CiHaNO 251717 CaHaNO 2262172 222 CaHnNSO 2230872 CoHoN,O 22549777 CotloN; 2262411 Cos 222.158 CoHoNs 234M CoHrO, 2251127 c, 2260994 CoHiN:Os 2220641 CuH5O, 2231699 CollyNO; 2251365 226.1233 CoH NO, 2220879 CuHasNO 223.1927 CjLAN5O, 225.1604 CotaNo 226.14 CoHaNAO, 2221118 Cu, 2232176 225.1842 CoHyO 2262298 C,HoNO, 2220766 CoHnO, 2230759 225.2081 CsHoN 2262536 ChHN5O, 222.1005 CisHaNO 223.0998 2025.0664 CoHuO 2261358 CoHiNsO, 222.1244 223.2063 225.0903 CH 226.1597 ChHaN;O 2221482 2232301 225.1142 Cita 226.2662 CNO, 221.940 223.1123 225.149 CoHo 226.1722 CoBO, 2220892 223.1362 225 1734 27 CoklaNO, 2221131 223.2427 225.1968 CioHisNaOa 227.1032 CiallN5O: 222.1369 2273.1488 225.2207 CoHNsO, 2271271 CoHaNGO 2221608 22500552 CotlyN4O, 227.1509 CoHaNa 2221846 CioHaN,O, 2240797 225.0790 GC. HyNO, 2271158 CoHNIO 2220668 Cio haNsOh 224.1036 225.1029 CH NO: 227.1635 CothaN, 2220907 CiHyN4O: 224.1275 CiFaNGO 2271873 Coll4O, 2221256 Cu NO, 2240923 CoH/N;O; 2270457 ChHyNO, 222.1495 ChHNO, 2241162 CoHN;O, 2270695 CoHoN,O 2221733 CH NO, 224.1400 > CoAN,O 2270934 CoHaN; 222192 ChHoN;O 224.1639 CiHO, CoHO, 2271284 CuHyN;O 2220794 CoHN,O 2240699 ColLoNO CaHaNO; 2271522 CuHaN, 2221032 CoeO, 2241049 CoHoN, 2251393 CoHoN.O, 2271761 HO, 222.1620 CiHaNO; 2241287 2252219 CaHosN5O 2271999 Ha, NO 222.1859 CoHoN,O, 224.1526 2252458 CoHyN, 2272238 aHaNo 2222098 CoHoNSO 2241764 2205.1280 CGHNO, 2270583 CaHO, 2220681 CoHaN, 2242003 CilhoN ChHNiO, 2274821 CoHNO 2220919 CiHN5O, 2240586 Cias 5 CoHaNsO 2271060 CoHaN, 2221158 CoHyuN;O 2240825 CoHa 225.164 CoHuN, 2271298 CoHxO 2221985 CaHoN, 2241063 26 CoHaNO, 227.1886 CosHaN 2222223 CotyO, 2241413 CoH;aN2O, 2260954 2272125 CoHuO 2224045 224.161 ColhaNSO, 226.1193 2272363 CoHN 2221284 224.189) CoHaNO, 226.143 227.708 Cia 222.2349 2242129 CuHNO, 226.1080 » 2270947 CNO 2219980 2240712 CuHN;O, 226.1318 Cut oN,O 227.1185 Cota 2221409 22441950 C..HaN50; 226.1557 CoHoN, 2271424 223 224.1189 CilLaNGO 226.1795 CuHsO, 2272012 Ci N;O4 2230719 21777 CoHN;O, 2260617 CuHaNO 2272250 CHaNiO, 2230958 224,2015 CoHNÇO 22611856 CoHO, 2271072 CoHyiNiO, 2231196 2242254 HOs 226.1205 CANO 227131 CuHNO, 2230845 2241837 CoHyNO; 226.1444 CoHoN: 227.1549 CuH;sN,O, 2231083 224,1076 CHHLN,O, 226.1682 CO 2272376 CuHN;O, 2273.1322 2241315 CoHN;O 226.1929 CoHN 2272615 CuHoNSO 223.1560 2204.2141 CoHaN, 2262160 CoHsO 2271436 CoHGN,O 2234621 2242380 CiHoNsO, 2260743 CidlaN 2271675 CaHsO, 2230970 21 CaHyoN;O 22640981 CoHa 227.1801 CoHNO, 223.1209 224.140 ColheN; 2261220 228 CoHNAO, 2273.1447 2242505 C:HyO, 226.1569 CoHiaNsO, 228.114 CoHaNsO 223.1686 224.156 CoHyNO, 226.180R CoHNiO; 228.1349 CoHaN, 2231925 CoHaNiO 226.2046 CoHoNiO, 2286.1588 ColNGO 2230746 CioHiaNaOa 2250876 CoHaN: 2262285 CNO, 2280648 CoHN, 2230085 Cie NÇOs 2251114 CuHhO, 2260630 ChHyNO, 2281236 CoHO, 2251334 CiotlyN4O, 225.1353 CuHoNO, 226.0868 CNO; 228.1475 CoHANO, CothaNO, 225.100] CaHyN;O 226.1107 CiHoN;O, 228.1713 CaNGO 2231811 CH N,O, 225.1240 CodleNS 226.1346 CHHyN,O 2281952 ColloN, 2232050 CuHoNiO, 225.1478 CuHxO, 226.1934 CoHiNOs 228.0535 62 Chapter? Mass Spectrometry Appendix A (Continued) FM FM EM FM CoHoNO 228.1012 CuHNO, 2291103 CoHoaNsO, 2311822 CoHoN, 2321690 CoHO, 2281362 CsHGNIO 229.1342 CuHN,O, 231.0406 CO, 2322039 Co H:NO, 228.1600 CuHoN, 2291580 CaHN;Os 2310644 CuHO; 2321100 CaHaN,O, 228.1839 ColyO, 2292168 CuHN,O, 231.083 CulLyNO, 232.138 CoHoN;O 228.2077 CuHaNO 229,2407 CuHyNO, 231.147] CuHyN,O 232.1577 CoFaN, 2282316 CsHyO, 229.1229 CiHo;N50, 2311710 CMN: 2321815 CaHO, 2280422 CHiNO 229.1467 CHo5N,0, 2311948 CoHoN, 2320876 CoHeNO, 2280661 CoHaN, 229.1706 CoHyN,O 2312187 CsH»O, 2321464 CoHoN,O, 2280899 CHlnO 2291593 CoHNO, 2310532 CsHaNO 2321702 Cola 228.1138 CoHaN 2291832 CoHnN,O; 231.0770 CsHaN, 232194 CoHyOs 2281726 CoHO 229,0653 CoHyNXD, 231.109 CoHyNO 232.0768 CoHaNO, 228.1965 CillhiN 2200892 CoH,N,O 231.1247 CitleN, 232400 CoHyN,O 228.2203 Cialis 229. 1018 CoH,O, 2311597 CoHO 2321828 CBN; 2282442 230 CoHasNO, 231.1835 CooHeN 232.2067 CuHO, 2280786 CioHyaN:Os 230.1267 CoHN$O, 2312074 CoHoO 232.088 CiaHhaNO, 228.1025 CiHaNiO, 230.1506 CoHyNsO 2312312 CoHN 2321127 CuHN,O 228.1264 CilaN4O, 230.174 CaHO, 231.0657 Coto 2322192 CuHaNs 2281502 CHAN; 2300566 CoHiNO; 2310896 CisHis 232,1253 CuHO, 2282090 CuHoNsO: 230.0805 CisHisNiO, 2311134 233 CuHaNO 228.2329 ChEoNO, 230.1393 CoHN5O 231.1373 ColbsNsO, 2331741 CaHoN, 2282567 C,N50, 230.163] CoHN, 2311611 CoHbaN4O» 233.1979 228157 CFaN5O, 2230.1870 CaHsO, 2310] CuHoN,O, 2330563 228.1389 CiHN4O 2302108 CoHNO, 231.1260 CoHNsO, 2330801 2281628 CoHNO, 2300453 CuHyoN,O 231.1498 CHHoNO, 2331628 2028.2454 Cio HN,Os 230.0692 2311737 ChHsN,O; 233.1866 228.1515 Co Ho N;O, 23041930 2310798 CHHyN;0, 233.2105 228, 1753 CoHyuN,O 230.1169 2311385 CoHiNO, 2330688 2280814 CoHO, 230.1518 231,1624 CoHNO, 2330927 228.1879 CoHyNO, 230.1757 2311863 CoHN.O, 233.1165 228.0939 NO, 230.1996 231.0684 CoHN,O 2331404 HaN;O 2302234 231,0023 CoHasO, 2331753 CioHGN:O, 229.1 189 CrHyN; 2302473 231.1750 CoHNO; 233.192 CotloNiO, 229.1427 CoHyO, 2300579 2310810 CaHiO 2330814 CotlyNsO, 229.166 CoHNO, 2300817 2311049 CaHiNO, 233.1052 CuH;N;O, 229.048 ColhaN;O, 230.1056 2312114 Co HNGO: ChHN,O, 2290726 CaHN;O 2301295 2311174 CaH NO 5 CiHaNO, 2291315 CoHhaN, 230,1533 CaHaN, 233.1768 ChHa NO, 229.1553 CoHxOs 2301883 232.1424 Cia Na CulbaN;O, 229179 CoHyNO, 230.212] ColLaN5O, 2321662 CuHHO, 2331178 CNO 2292030 CoHaNGO 230.2360 CioHaN,O, 232.190] CuHyNO, 2331416 CoHN;O, 2290614 CuHO, 2300943 CoHsN,O, 2320484 CuHaN.O 2332.1655 CoHNO, 2729.0852 CuBNO, 2301182 CaHNSO, 2320723 CaHoN,O 2330715 ColaNSO 229.109 CsHaNZO 230.1420 CiHN4O, 232.096] CoHoNo 2330954 CollyO, 2291440 CuHaN, 2301659 ChHoNO, 232.1549 CuHO, 2331542 CoHNO, 2294.1679 CuHyO, 2302247 CuHaN,O; 2321788 CiHaNO 2331781 CioHa;N,O, 229.1917 CaHO, 2301307 CuHssN5O, 232.2026 CiHaN, 2332019 CoHaNO 2292156 CoHyNO 230,1546 CoHyNSO 2322265 CiH5O, — 233.0603 CoHoN, 220,2294 Colo, 2301784 CoHyNO, 2320610 CiaHnNO 233/0841 CaH5O, 229.0501 CuHoN, 230.0845 CoHyN,O, 2320848 CoHaN, 2331080 CoHNO, 2294739 CiHoO 230.167] CoHN;O, 2321087 CHisO 2331906 CoaHlysN,O, 2290978 CooHN 2301910 CiHeN4O 2321325 CoHaN 2332145 CalhaNSO 2291216 CotlyO 2300732 CoMo 32.1675 CotlaO 2330967 CoHyN, 229.145 CollaN 2300970 CoH. 232.1914 CollaN 2331205 CoHO, 229.1804 CH 230.2036 CoHgN,O; 2322152 Citi 2332270 Co HO, 2279.2013 CH 230.1196 CoHeO, 7320735 CB 233.133] CratoN;O 229.228] 2 CaHNO, 2320974 234 CollyNs 2290.2520 CoHyN;Os 231.1345 CialboN5O, 2322.1213 CioHyN,O, 234.1580 CHnO, 2200865 CioHaiN40; 231.1584 CoHiaNSO 232.149] CidLaN5O, 234.1819 Appendix A (Continued) AppendixA 65 FM FM FM FM CuHiNO, 245.1052 CHlyNo 2462098 CoHNsO; 248.1036 CoHhyN,O 2491968 CNO, 245.1291 CrHyO, 2460681 CoHeN,O, 248.1275 CoHN; 2492207 CHyNiO 2451529 CoHaNO 2460919 CoHyNO, 248.1863 CiHNO, 2490790 CoHyN, 2451768 CoHuN, 2461158 CraHaaN20, 248.2101 CoHaN;O 249.1029 CoHyO, 2452117 CoHyO 2461985 CaHNO, 2480923 CoHN, 2491267 CHyNO, 245.2356 CoHaN 2462223 CoHN;O, 248.1162 CoHlsO, — 249.1855 CoHO, 2451178 CoH4O — 246.1045 CiHN:O, 248.1400 CoHyNO 249.2094 CsHNO, 245.1416 CaHiN 2461284 CoHoN,O 248.1639 CisHaNo 249.2332 CH N$O 245.1655 Ciao 246.2349 ColxO, 248.198 CoHO, 2490916 CisHaNs 2451894 CoHhy 2461409 CuHO, 2481049 CoHiNO 249.1154 CiHN;O 245.0715 247 CuHooN;O, 248,1526 CoHiN, 2491393 CillhiN, 245.0954 ChHaN,O4 247.1659 CuHoN;O 248.1764 CoHsO 2492219 CrHyO, 2451542 Ch HsN;O, 247.1897 CuHaN, 2482003 CoHaN 2492458 CoHaNO 2451781 C.HN,O, 2472136 CilhoN;O 2480825 CoHçO 249.1280 CisHaeN, 245.2019 CH N5Oa 2470719 CoHaN, 248.1063 ColhoN 249.1519 CoHNO 2450841 CHNSOs 247.0958 CsHyO; 2481413 Cita 2492584 CoHhNo 245.1080 CoHisN4O, 247.1196 CoHNO, 248.1651 CsoHay 249. 1644 ColO 245.1906 CoHiNO, 2471784 CsH,iN2O 248.1890 250 CotlyN 2452145 CioHo/N,Os 247.2023 CisHooNa 2482129 C)HaN,O, 2501894 CllsO 2450967 CiHogN;O, 2472261 CiHoNO, 2480712 Ci HN,Os 25010954 CaHgN 2451205 CoHoNO, 2470845 Cio NDO 2480950 CiHhoN5O; 250.1193 CuHos 245.270 ; 2471083 CiohaN5 248.1189 CrHN4O, 250.143 CH; 2451331 2471322 CoHyO, 2481777 CaHeNO, 250.1080 26 2471560 CoHNO 248.205 CaHsN5Os 250.1318 CuHLoN;O, 246.1580 K 2471910 CioHaNo 2482254 CoHyN50, 250.1557 ChHN5O; 246.1819 CollsNO, 2472148 ChHvO, 2480837 CoHaN,O 250.1795 CoHaeN 40, 246:2057 CoHsO, 2470970 ColhaNO 248.1076 CuHoN,O 2500856 Cia N;O, 2460641 CLHiNO; 247.1209 ColaN, 2481315 CHlyNO, 2501444 CoHN;O, 246.0879 CuHN,0, 247.1448 CoHO 248214 CuHoN;O, 250.1682 CoHaNiO, 246.1118 CaHaN5O 247/1686 CoHyN 2482380 CHo,NGO 250.192 CoHyNO, 246.1706 CilboNo 2471925 CoHyO 2481202 CuHoN, 2502160 CoHyN5O; 246.1945 CuHGNSO 2470746 CotluN 248/1440 CisHroN,O, 250.0743 Co HaaN5O, 2462183 CoHN, PATA9ES Cata 248.2505 CHaN;O 2500981 CoHaN4O 246.242 CiHO, 247.1334 Coto 2481566 CotlaN4 250.1220 CollaNO, 2460766 CsHaNO, 2471573 249 CisHrOs 2501569 CatfuN;O; 246.1005 CoHyNAO 2471811 CoHsN;O, 249/1815 CisHyNO, 250.1808 CoH NO, 2461244 CoHaN; 2472050 Ch H;N5O; 249.2054 CisHogN;O 250.2046 CaHaN,O 246.1482 CB NAO 2470872 CrHaN,04 2490876 CilloN; 2502285 CoHxO, 2461892 CiHaNs 24711] CaH,N5O; 249.114 CiHO, 2500630 CalliNO, 2462070 Co) 2471699 CoH,N,O, 249.1353 CiHNO, 2500868 Ci HyiN5O, 2462309 CoHsNO 247.1927 CaHyNO, 2491941 CiHN,O 250,1107 CoHO, 2460892 CeHaGN, 2472176 CHheNO, 249.1001 CrtleN; 2501346 CaH NO; 246.1131 CoHiO, 2474759 CHINO; 249.1240 CrolxO, — 250.1934 ChaHL NO, 246.1369 CoHoNO 247.0998 CoHN;0, 249.1478 CHNO 2502172 CuHooN5O 2461608 CoHN, 2471236 CoHaN4O 2491717 CioHaoN, 2502411 CoHoN, 246.1846 E 2472063 CuHN,O 249.077 CoHuO, 2500994 CuHwO, 2462196 2472301 CalliO, 2491127 CNO 250/1233 CosoNo 2460907 s 247.123 CuHNO, 2491365 CoaNo 2501471 CH4O, 2461256 CoHyN 2471362 CHINO, 249.1604 CHyO 2502298 CisHyNO, 246.1495 CuHls; 2472427 CuHaN;O 249.1842 CoaHoN 2502536 CisHaN5O 246.1733 CisHhy 247.1488 CuHosNs 2492081 CaHlyO — 250.1358 CoHaN, 2461972 248 CosHNH), 24911664 CouHyN 2501597 Cotta 246.0794 C.HuNçO, 2481737 CaHnN;O 249.0903 Coll 250.2662 CeHaN, 246.1032 CoHaN5O, 2481976 CoHN, 2491142 Cola 250.1722 CHyO, 246.1620 ChHyN,O, 2482214 CreHyiO, 249.1491 CioHaNO 246.1859 CoHoN;Os PASUTIT CHyNO, 249.1730 66 Chapter? Mass Spectrometry Appendix B Common Fragment lons All fragments listed bear +1 charges, To bc uscd in conjune- tion with Appendix C. Not all members of homologous and isomeric series are given. The list is meant to be suggestive rather than exhaustive. Appendix LL of Hamming and Foster (1972), Table A-7 of McLafferty's (1993) interpretative book. and the high-resolution ion data ot MeL afferty (1982) are rec- ommended as supplemcnts. Structural inferences arc listed in parenthescs mfz lonsº (Structural Inference) Mo cm q 15 CH; I 6 O 59 (CH),COH, CHOC.H, C—OCH, (RCO,CH,). 7 OH 18 HO,NH, NHC=0 + H, CH,OCHCH,, CH,;CHCH,0OH, 19 FHO Í 26 N, CH CH. 27º CH CHCHOH 28 CH, CO,N, (air), CH-NH 29 CH, CcHO o 30 CH;NH, (RCH;NH,), NO / . 31 CIGOH(RCH,0H), OCH; 60 CHC —H, CHONO 2 O (air) 0H 33 SH.CHF 34 HS 9 35 CI(Clat37) 36 HCI(H "Clat 38) 42º CH, GHO 8 CH, CH;C=0, CH;C=06, (G = R, Ar, NH,, OR. 0H), C,HaN H I 44 CHC=0 + H (Aldchydes, Mel afferty rearrangement), CH;CHNH,, CO, NH;C=0 (RC=0ONH;), (CH,);N cH, as demon, CH,CH,OH, CH;OCH, (RCH,0OCH,), o bom, CILCH—O + H (CH;CHOBR) 46 NO, 47 CH;SH (RCH;SH), CILS 48 CH$+H 49 CILCI(CH, SClat5t) SL CHE, CH, (CH;)NCH,. C)H;NHCH,, CS | 61 CHC—O + 2H, CH,CH,SH, CH.SCH, 65 CH 66 O CH, ES, (RSSR) 67 CH 68 CH;CH,CHC=N 69 CH, CF, CHCH=CHC=0, CH,=C(CHC=0 Mo CHy 7º GH. CHC=0 o A CH H, CACUNIL, 72 CH, (CILN=C=0, CHNHCHCH, and isomers 73 | Homologs of 59, (CH,),Si o I 7 CH—C—OCH, +H | 7 75 € OCL + 2H, GHCO +2H, CH; (CH: CSH, (CH,0),CH, (CHy;SION 7% CA (CHX CGAXY) 7 CHÁCHX) 78 CGH-H 79 CM, +2H,Br(Brat81) Appendix B Continued 2.10 Mass Spectrum of Some Chemical Classes 67 m/z Jonst (Structural Inference) o iris re(OT E ' . 92 CH, “+ H, N N | + LO | t N H, 4 a s ; CHSS + Hi Be (HEBr at 82) 93 CHBr(CHABrat 95, RCH.Br). CHs, AO s [| = [O] 4 CH, (terpenes) Lo Lg, CH, sy E=0, “o 82 — CH,CH,CH,CH,CSN, CCI, (CSCISCI at 84, a +, -JHe-o CFC, at 86), Ciro A Né H 83 CH, CHCI, (CHECKCI at 85, CHNCL at 87), 95 l Sre=o E o Se s 96 CH;CHCH,CH,CH,C 85 CH CHC=0,CCIF, (C"CIK, at 87), ” cata rem $ o q O o 8 86 cH; +H, CCHNH, and isomers 9 CH CH, CH, uv” So 8” í 100 CHE +H, CH. CLNH, 87 CASCO, homologs of 73, CHCHAÇOCII, Net, o 7 9 101º C—OCH 88 CH—C—OCH,+H o o 102º CHC—OCH,4 H | c 89 C-ocH,+2H, 9 103 COCA, + 2H, CH,S, CH(OCH;CH): cH 104 CH,CHONO, 99 — CH,CHONO,, o 91 + . 105 . O CH, (C;H,CH,Br). CH+H, CGHAC=0)GIG = OH, OR, UAr, halogen, c NH, CH,CH, —CHCH, (OT +2H, O N 106 NHCH, (CH, CM (CH SCI, at 93], OT EN O 70 Chapier2 Mass Spectrometry Appendix € Coniinued Motecutar lon Minus Fragment Lost (Inference Structure) 56 €H,—CHCH,CH,. CH;CH=CHCH; 2CO 57 CaHy* (butyl ketones), CALISCO (ethyl ketones, EIC=0G, G — various structural units) ss -NCS, (NO + CO), CH;COCH;. CH, 39 60 C.H,0H, CH;=C(OH), (acetate esters)* H i g. 61 CICS. ZA 62 (HS and CH;=CH;) 63 “CH,CICI 64 Call, 8, SO, cH, 68 CH=C—cH=CH, 69 CE 7 CH o 3 cncnob. E CHOH FB CAd, % CH, CS, n Cl, CSH E CH CS4Hy, CHAN m Bro, GH so HBr ss “Cor, 100 CE,==CH, 119 CE—CE, 122 CHsCOOH 127 r 128 HI * MeLalferty rearcangement. CHAPTER 3 Infrared Spectrometry E 3.1 Introduction Infrared (TR) radiation refers broadly to that part of the electromagnetic spectrum between the visible and mi- crowave regions. Of greatest practical use to the organic chemist is the limited portion between 4000 and 400 cm!. There has bcen some interest in the near- IR (14,290-4000 em!) and Lhe far-IR regions. 700- 200 em! From the brief theoretical discussion Lhat follows, it is clear that even a very simple molecule can give an extremely complex spectrum. The organic chemist takes advantage of this complexity when matching the spec- trum of an unknown compound against that of an au- thentic sample. A peak-by-peak correlation is excellent evidence for identity. Any two compounds, except en- antiomers, are unlikely to give exactly the samc IR spec- tum. Although the IR spectrum is characteristic of the entire molecule, it is true that certain groups of atoms give rise to bands at or near the same frequency regard- Jess of the structure of the rest of the molecule. Tt is the persistence of these characteristic bands that permits the chemist to obtain useful structural information by simple inspection and reference to generalizcd charts of characteristic group frequencies. Wc shall rely heavily on these characterislic group frequencies. Since we are not solely dependent on IR spectra for identification. a detailed analysis of the spectrum will not be required. Following, our general plan, we shall present only sufficient thcory to accomplish our pur- pose: utilization of IR speetra in conjunction with other spectral data in order to determine molecular structure. The importance of IR spectrometry as a tool of the practicing organic chemist is readily apparent from the number of books devoted wholly or im part to discus- sions of applications ol IR spectrometry (sec the refer- ences al fhe end of this chapter). There arc many com- pilations of spectra as well as indexes to spectral na collections and to the literature. Among the more com- monly used compilations are those published by Sadtler (1972) and by Alkrich (1985). 3.2 Theory Infrared radiation of frequencies Jess than about 100 cm is absorbed and converted by an organic mol- ecule into cnergy ot molecular rotation, This absorption is quantized: thus a molecular rotation spectrum consists of discrete lines. Infrared radiation in the range from about 10,000- 100 em”! is absorbed and converted by an organic mol- ecule into energy of molecular vibration. This absorp- tion is also quantized, but vibrational spectra appcar as bands rather than as lines because a single vibrational energy change is accompanied by a number of rota- tional energy changes. Tt is with these vibralional-ro- tational bands, particularly those occurring between AQ0O and 400 em”, that we shall be concerned. "Lhe fre- queney or wavelength of absorption depends on the rel- ative masses of the atoms, the force constants of the bonds, and thc geometry of the ators. Band positions in IR spectra are presented here as wavenumbers (7) whosc unit is the reciprocal centi- meter (cm! this unit is proportional to the energy of vibration and modern instruments arc linear in recip- rocal centimeters. Wavelength (A) was used in Lhe older literature in units of micrometers (um = 10-º m; earlier called microns). Wavenumbers are reciprocally related to wavelength. emo! = 10gm Note thal wavenumbers are sometimes called “fre- quencies.” Lowever, this is incorrect sinec wavenum- bers (7 in units ot em !) are equal to 1 x 10º im units ot gm, whercas frequencies (vin Hz) are equal to c/À in em, c being the speed of light (3 x 10º em/s). The 72 Chapter3 Infrared Spectrometry symbol 7 is called “nu bar.” Our spectra are linear in cm”! except for a few lincar in um. Note also thal these spectra are different from one another in appearance (sec Tig. 3.6). Band intensities can be expressed either as trans- mittance (7) or absorbance (A). Transmittance is the ratio of thc radiant power transmitted by a sample to the radiant power incident on the sample. Absorbance is the logarithm, to the base 10, of the reciprocal of the transmittanec; 4 = logy (1/7). Organic chemists usually report intensity in semiquantitative terms (s = strong, m = medium, w = weak). There are two types of molecular vibrations: strotching and bending. A stretching vibration is a rhythmical movement along the bond axis such that the interatomic distance is increasing or decreasing. A bending vibration may consist of a change in bond angle between bonds with a common atom or the movement of a group of atoms with respect to Lhe remainder of the molecule without movement of thc atoms in the group with respect to one another. For cxample, twisting, rocking. and torsional vibrations involve a change in bond angles with reference to a set of coordinates ar- bitrarily set up within the molecule. Only those vibrations that result in a rhythmical change in the dipole moment of the molecule are ob- served in the IR. The alternating electric held, produced by the changing charge distribution accompanying a vi- bration, couples the molecule vibration with the oscil- lating electric ficld of the electromagnetic radiation. A molecuic has as many degrees of freedom as the total degrees of freedom of its individual atoms. Each atom has threc degrees of freedom corresponding to the Cartesian coordinates (x, y, z) necessary to describe its position relative to other atoms in the molecule, A mol- ecule of 1 atoms therefore has 3r degrees of freedom. For nonlinear molecules, three degrees of freedom de- seríbe rotation and three describe translation; the re- maining 3n — 6 degrees of freedom are vibrational de- grees of freedom or [undamental vibrations. Linear molecules have 32 — 5 vibrational degrees of freedom, for only two degrees of freedom are required to describe rotation. Fundamental vibrations involve no change in the center oJ gravity of the molecule. The three fundamental vibrations of the nonlinear. triatomic water molecule can be depieted as follows: Symmetrical Asymmetrical Seissoring stretching (vs OH) stretching (tras OH) (ôs HOH) 3652 cmTl 3756 cm” 1 1596 cm” 1 Note the very close spacing of the interaeting or coupled asymmetric and symmetric stretching, above, compared with the far-removed seissoring mode. The CO, molecule is linear and contains three atoms; therefore it has four fundamental vibrations [Gx3-—5]. Bo (1) Symmetrical stretching (vs CO2) 1340 em” + — 0 és (3) Scissoring (ending) (ês CO2), 666 em” »—— E) —o (2) Asymmetrical stretching (vas COg) 2350 emo! (4) Scissoring (bending) (8, COp), 666 em! The symmetrical stretching vibration in (1) above is inactive in the IR since it produces no change in the dipole moment of the molecule. The bending vibrations in (3) and (4) above are equivalent and are the resolved components of bending motion oriented at any angle to the internuclear axis: they have lhe same frequency and are said to be doubly degenerate. The various stretching and bending modes for an AX, group appearing as a portion of a molecule, for example, the CH. group in a hydrocarbon molecule, are shown in Figure 3.1, The 34 — 6 rule does not apply since the CH, group represents only a portion of a mol- ecule, The theoretical number of fundamental vibrations (absorption frequencies) will seldom be observed be- cause overtones (multiples of a given frequency) and combination tones (sum of two other vibrations) in- crease the number of bands, whercas other phenomena reduce the number of bands. The following will reduce the theoretical number of bands. 1. Fundamental frequencies that fall outside of the 4000-400 em region”. 2. Fundamental bands that are too weak to be ob- served. 3, Fundamental vibrations that are so close that they coalesce, 4. The occurrence of a degenerate band from several absorptions of the same frequency in highly sym- metrical molecules. 5. The failure of certain fundamental vibrations to ap- pecar in the TR because of the lack of change in mo- Iccular dipole. Assignments for stretching frequencies can be ap- proximated by the application ot Hooke's law. In the application of the law, two atoms and their connecting C11240-2 CAS [7120-92-39] o FW 8412 Cyclopentanons, 99 + % me -51ºC bp 13043106 Wavalangth, (am) a Ta WAVENUMBERS tom!) FIGURE 3.2. Cyclopentanone, thin film. bration occurs near 666 em 1334 cm”!. Fermi resonance is a common phenomenon in IR and Raman spectra, It requires that the vibrational lev- els be of the same symmctry species and that the inter- acting groups be located in the molecule so that me- chanical coupling is appreciable. An example of Fermi resonance in an organic struc- ture is the “doublet” appearance of the C=O stretch of cyctopentanone under sufficient resolution condi- tions. Figure 3.2 shows the appearance of the spectrum of cyclopentanone under the usual conditions. With ad- equate resolution (Fig. 3.3), Fermi resonance with an overtone or combination band of an a-methylene group shows two absorptions in the carbons) stretch region. !, the first overtone near 3.2.2 Hydrogen Bonding Hydrogen bonding can occur in any system containing a proton doner group (X—H) and a proton acceptor WAVENUMBER (om?) 1740 1780 1740 1780 1740 1780 1740 1780 TTTR ITTT TTTT TTT z 2 E + E ê < sf A E z 8 T 5 + s + A B c D LILI LILI LIA a FIGURE 43. Infrared spectrum of eyclopentanone in variaus media. A. Carbon tetrachloride solution (0.15 M). B. Carbon disulfide solution (0.023 M). €. Chloroform solution (0.025 44). D. Liquid state (thin films). (Computed spectral slit width 2 em !) 32 Theory 75 dog IR HE, 255C. 2966.1 12782 8342 Fperer NMR E 1,393 17484 11530 5822 ng 1.4359 Merck 10,2736 14076 0592 4717 RAP A o tas dm O méme o! “oa NIGOLEY 205X FTHR (Y) if the s orbital of the proton can elicetively overlap the p or 7 orbital of the acceptor group. Atoms X and Y are electronegative, with Y possessing lone pair elcc- trons. The common proton donor groups in organic molecules are carboxyl, hydroxyl, amine, or amide groups. Common proton acceptor atoms are oxygen. ni- trogen, and the halogens. Unsaturated groups, such as the C=C€ linkage, can also act as proton acceptors. The strength of the hydrogen bond is at a maximum when the proton donor group and the axis of the lone pair orbital are collinear, The strength of the bond de- creases as Lhe distance between X and Y increases. Ilydrogen bonding alters the force constant of both groups: thus, the frequencies of bolh stretching, and bending vibrations are altered. The X—H stretching bands move to lower frequencies (longer wavelengths) usually with increased intensity and band widening. The stretching frequency of the acceptor group, for example, C€=o0, is also reduced but to a lesser degree than the proton donor group. The H—X bending vibration usu- ally shifts to a shorter wavelength when bonding occurs; this shift is less pronounced than that of the stretching frequency. Intermolecular hydrogen bonding involves associa- tion of two or more molecules of the same or different compounds. Intermolccular bonding may result in di- mer molecules (as observed [or carboxylic acids) or in polymeric molecular chains, which exist in ncat samples or concentrated solutions of monohydroxy alcohols. fn- tramolecular hydrogen bonds are formed when the pro- ton donor and acceptor are present in a single molecule under spatial conditions that allow the required overlap of orbitals, for example. the formation of a five- or six- membered ring. Lhe extent of both inter- and intra- molecular bonding is temperature dependent. The effect of concentration on intermolecular and intra- molecular hydrogen bonding is markcdly different. The 76 Chapter3 Infrared Spectrometry Table 3,1 Stretching Frequencies in Hydrogen Bonding Intermolecular Bonding Intramolceular Bonding Frequency Frequency Reduction Reduction Xx-H-Y (em 9 tem 1) Strength Voa Bo Compound Class von pe=o Compound Class Weak 300º ! 15º Alecohols, phenols, and inter- < 1004 10 1,2-Diols, e- and most B-hydroxy molecular hydroxyl to car- ketanes; o-chloro and o-al- bonyl bonding koxy phenols Medium 100-300% 50 1,3-Diols; some 2-hydroxy ke- tones; B-hydroxy amino com- pounds; B-hydroxy nitro com- pounds Strong >500º 50 — RCO,H dimers >300º 100 — o-Hydroxy aryl ketones; o-hy- droxy aryl acids; o-hydroxy aryl esters; 8-diketones; tropo- lones «Frequency shift relative to “free” stretching frequencies. * Carbonyl stretching only where applicable. bands that result from intermolecular bonding gencrally disappear at low concentrations (less than about 0.01 M in nonpolar solvents). Intramolecular hydrogen bond- ing is an internal effect and persists at very low concen- trations. The change in frequency between “free” OH ab- sorption and bonded OH absorption is a measure of the strength of the hydrogen bond. Ring strain, molecular geometry, and the relative acidity and basicity of the proton donor and acceptor groups affect the strength of bonding. Intramolecular bonding involving the same bonding groups is stronger when a six-membered ring is formed than when a smaller ring results from bonding. Hydrogen bonding is strongest when the bonded struc- ture is stabilized by resonance. The effects of hydrogen bonding on the stretching frequencies of hydroxyl and carbonyl groups are sum- marized in Table 3.1. Figure 3.17 (spectrum of eyclo- hexylcarbinol in the stretch region) clearly illustrates this effect. An important aspect of hydrogen bonding involves interaction between functional groups of solvent and so- lute. If the solute is polar, then it is important to note the solvent used and the solute concentration. 3.3 Instrumentation 3.3.1 Dispersion IR Spectrometer For many years, an infrared spectrum was obtained by passing an infrared beam though the sample and scan- ning the spectrum with a dispersion device (the familiar diffraction grating). The spectrum was scanned by ro- tating the diffraction grating; the absorption areas (peaks) were detected and plotted as frequencies versus intensities. Figure 3.4 demonstrates a sophisticated double- bcam dispersion instrument, operation of which in- volves splitting the beam and passing one portion through the sample cell and the other portion through the reference cell. The individual beams are then recom- bined into a single beam of alternating segments by means of the rotating sector mirror, M7, and the ab- sorption intensities of the segments are balanecd by the altenuator in the reference beam. Thus, the solvent in the reference cell and in the sample cell are balanced out, and lhe spectrum contains only the absorption peaks of the sample itself. 3.3.2 Fourier Transform Infrared Spectrometer (Interferometer) Fourier transform infrared (FT IR) spectrometry has been extensively developed over the past decade and provides a number of advantages. Radiation containing all IR wavelengths (e.g., 5000-400 cm !)is split into two bcams (Fig. 3.5). One beam is of fixed length, the other of variable length (movable mirror). The varying distances between two pathlengths result in a sequence of constructive and destructive in- terferences and hence variations in intensities: an inter- ferogram. Fourier transformation converts this interfer- ogram from the time domain into one spectral point on the more familiar form of the frequency domain. PHOTOMETER MONOCHROMATOR (GRATING) 34 Sample Handing 77 FIGURE 34, Optical system of double-beam TR spectrophotometer. Smooth and continuous variation of the length of the piston adjusts the position of mirror B and varies the length of beam B; Fourier translormation at successive points throughout this variation gives rise to lhe com- plete IR spectrum. Passage of this radiation through a sample subjecis the compound to a broad band of en- ergies. In principle the analysis of one broadbanded pass of radiation through the sample will give rise to a com- plete IR spectrum. There are a number of advantages lo FT IR meth- ads. Sinec a monochromatot is not used, the entire ra- diation range is passed through the sample simulta- necusly and much time is saved (FelgetU's advantage); Mirror drive Piston Mirror B (movable) Mirror À Source (xe) Beam splitter Combined beam [E Jsampie cen EI Detector CI Analog to digital converter computer D+ FIGURE 3.5, Schematic of an FT IR speclromcter Recorder FT IR instruments can have very high resolution (50.001 em"), Moreover since the data undergo ana- Jog-to-digital conversion, IR results are easily manipu- lated: Results of several scans arc combined to average out random absorption artifacts, and excellent spectra from very small samples can be obtained. An FT IR unit can therefore be used in conjunetion with HPLC or GC. As with any computer-aided spectrometer, spectra of pure samples or solvents (stored in the computer) can be sublracted from mixtures. Flexibility in spectral printout is also available: for example, spectra linear in either wavcnumber or wavelength can be obtained from the samc data set. Several manufacturers offer GC-FT IR instruments with which a vapor-phase spectrum can be obtained on nanogram amounts of a compound eluting from a cap- illary GC column. Vapor-phasc spectra resemble those obtained at high dilution in a nonpolar solvent: Con- centration-dependent peaks are shifted to higher fre- quency compared with those obtained trom concen- trated solutions, thin films, or the solid state (see Aldrich, 1985). 3.4 Sample Handling Infrared spectra may be obtained for gases, liquids, or solids. The spectra of gases or low-boiling liquids may be obtaincd by expansion of the sample into an evacu- ated ecll. Gas cells arc available in lengths of a few cen- timeters to 40 m. The sampling arca of a standard IR speetrophotometer will not accommodate cells much longer than 10 cm: long paths are achieved by multiple reflection optics. Liquids may be examined neat or in solution. Neat liquids are examined between salt plates, usually with- out a spacer. Pressing a liquid sample between fiat plates produces a film 0.01 mm or less in thickness, the plates being held together by capillary action. Samples of 1-10 mg arc required. Thick samples of neat liquids 80 Chapicr3 Infrared Spectrometry spectrum, arising from C—H stretching vibrations of the aldehyde group. Simitarly, the assignment of a car- bonyl band to an ester should be confirmed by obser- vation of a strong band in the C—O stretching region, 1300-1100 cm, Similar compounds may give virtually identical spectra under normal conditions, but fingerprint differ- ences can be detected with an expanded vertical scale or with a very large sample (major bands off scale). For example. pentane and hexane are essentially indistin- guishable under normal conditions and can be differ- entiated only at very high recorder sensitivity. Finally, in a “fingerprint” comparison of spectra, or any other situation in which the shapes of peaks are 182427 CAS [9003-536] cn Poly(styrene) fem qu da GMs important, we should be aware oí the substantial differ- ences in the appearance of the spectrum in changing from a spectrum that is linear in wavenumber to one that is linear in wavelength (Fig. 3.6). Admittediy, the full chart of characteristic absorp- tion groups (Appendix €) is intimidating. The following statements and simplified chart may help (Fig. 3.7). Thc first bit of advice is negative: Do not attempt a frontal, systematic assault on an infrared spectrum. Rather, look for evidence of the presence or absence of a few common functional groups with very character- istic absorptions. Start with OH, C=0, and NH groups in Figure 3.7 sinec a “yes/no” answer is usually avail- ablc, A “yes” answer for any of these groups sharpens IR, 1599F 29240 12181] 7574 Merck 10,8732 16008 10281 6978 14926 9064 540.1 DE WAVENUMBERS (cm!) ta) WAVENUMBERS (cm?) 3000 2000 1500 Percent transmittance 3 4 5 6 7 8 9 Wavelength, (am) (b) Polysiyrene, same sample for both (a) and (5). Spectrum (2) linear in FIGURE 3.6. wavenumber (cm 9; spectrum (6) tinear in wavelength (um). 1000 900 700 100 g 8 8 Percent transmittanca 10 11 13 14 36 Characteristic Group Absorptions of Organic Molecules 81 em! 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 000 aoo T T a800 | 3600 ! 3000 | 2600 m Alkenes Alkynes m/sh s/br| one po DESA do Aromatics mw NO, p= mama tfooao === 8=0 0=5=0 aBoo 3400 3000 2600 2200 L L1 l l Li a j eml 4000 3600 3200 2800 2400 2000 1800 Free OH, medium and srarp; bonded OH, strong and brozd 160 1400 1200 ICO 80 eco FIGURE 3%, Simplified chart of several common functional groups with very characteristic absorptions. s = strong, m = medium, w = weak, sh = sharp, br — broad. the focus considerably. Certainly the answer will con- tribute to development of a molecular formula from the mass spectrum and to an entry point for the NMR spec- tra. These other spectra, in turn, will suggest further leads in the IR spectrum. Figure 3.7 lists the common groups that provide distinctive, characteristic absorptions. Section 3.6 fur- nishes morc detailed information — including a number of caveats, 3.6 Characteristic Group Absorptions of Organic Molecules A table of characteristic group absorptions is presented as Appendix C. The ranges presented for group absorp- tions have been assigned following the examination of many compounds in which the groups occur. Although the ranges are quite well defined, the precise frequency or wavelength at which a specific group absorbs is de- pendent on its environment within the molecule and on its physical state. This section is concemned with a comprehensive look at these characteristic group absorptions and their relationship to molecular structure. As a major type or class of molecule or functional group is introduced in the succeeding sections, an example of an IR spectrum with the important peak assignments will be given. Spectra of common laboratory substances, representing many of the chemical classes listed below, are shown in Appendix B. Characteristic group absorptions are found in Appendix C. 3.6.1 Normal Alkanes (Paraffins) The specira of normal alkanes (paraffins) can be inter- preted in terms of four vibrations, namely, the stretch- ing and bending of C—H and C—C bonds. Detailed analysis of the spectra of the lower members of the al- kane series has made detailed assignments of the spec- tral positions of specific vibrational modes possible, Not all of the possible absorption freguencies of the paraffin molecule are of equal value in the assignment of structure. The C—C bending vibrations occur at very low frequencies (below 500 em!) and therefore do not appear in our spectra. The bands assigned to C—C stretching vibrations are weak and appear in the broad region of 1200-800 cm-!; they are generally of little value for identification. “The most characteristic vibrations are those arising from C—H stretching and bending. Of these vibrations, those arising from methylene twisting and wagging are usually of limited diagnostic value because of their weakness and instability. This instability is a result of strong coupling to the remainder of the molecule. The vibrational modes of alkanes are common to many organic moleculcs. Although the positions of C—H stretching and bending frequencies of methyl and methylene groups remain ncarly constant in hydro- 82 Chapier3 Infrared Spectrometry carbons, the attachment of CH, or CH, to atoms other than carbon, or to a carbonyl group or aromatic ring, may result in aprreciable shifis of the C—H stretching and bending frequenei The spectrum of dodecane, Figure 3.8, is that of a typical straight-chain hydrocarbon. 361.1 C—H Stretching Vibrations Absorption arising from C—H stretching in the alkanes occurs in the general region of 3000-2840 em 1. The positions of the C—H stretching vibrations are among thc most sta- ble in the spectrum. Methyl Groaps An cxamination of a large num- ber of saturated hydrocarbons containing methyl groups showed, in all cases, two distinct bands occurring at 2962 and 2872 cm-!. The first ol Lhese results from the asym- metrical (as) stretching mode in which two C—H bonds of the methyl group are extending while the third one is contracting (»,CH;). The second arises from sym- metrical (s) stretehing (»CH,) in which all three of the €-— H bonds extend and contract in phasc. The pres- ence of several methyl groups in a molecule results in strong absorption at these positions. Methylene Groups The asymmetrical stretching (Cr CH,) and symmetrical stretching (»CH;) oceur, re- spectively, near 2926 and 2853 em !. The positions of these bands do nol vary more than + 10 cm ! in the aliphatic and nonstrained cyclic hydrocarbons. “The fre- quency of methylene stretching is increased when the methylene group is part of a strained ring. 3.6.1.2 C—H Bending Vibrations Methyl Groups Two bending vibrations can occur within a methyl D22110:4 CAS[112403] — cnfen,) CH FW 170.34 Dodacans, 99% bem) ch, mp -8.6º€ bp 215-217ºC ti 20 24 A Ro ar asa os as sos FIGURE 38. Dudecanc. A. The € Wavelength, (am) $ 7 ' 1800 ' WAVENUMBERS (cm!) H streteh: 2962 em-! v, CH, 2872 cm ! CH, 2924 emo! vu CHo, 2853 emo! CH, B. The C—H bend: 1447 em! 8,CH,, 1450 em 80H 1378 em ! 8€CH, €. The CH, rock: 721 cm! p CH, group. The first of these, the symmetrical bending vi- bration, involves the in-phase bending of the C—H bonds (1). The second, the asymmetrical bending vi- bration. involves out-of-phase bending of the C—H bonds (MT). zm) H ( H : I H In E, the C—H bonds are moving like the closing petals of a flower; in 11, enc petal opens as two petals close. The symmetrical bending vibration (3,CH;) occurs near 1375 em?, the asymmetrical bending vibration (8.CH;) near 1450 em 1. The asymmetrical vibration generally overlaps Lhe scissoring vibration of the methylenc groups (see be- low). Two distinct bands are observed, however, in com- pounds such as diethyl ketone, in which the methylenc scissoring band has been shifted to a lower frequency, 1439-1399 em !, and increased in intensity because of its proximity Lo the carbanyl group. The absorption band near 1375 em", arising from the symmetrical bending of the methyl C—H bonds, is very stable in position when lhe methyl group is at- tached to another carbon atom. The intensity of (his band is greater for each methyl group in the compound than that for the asymmetrical methyl bending vibration or the methylene scissoring vibration. Methylene Groups The bending vibrations of the C—H honds in the methylene group have been shown schematically in Figure 1, The four bending vibrations 80.749 IRIL SA 2024 7211 Fp 180ºF NMR IL 1,114 14673 nB 1.4212 13782 | ii lii as ei “ão NICOLET 205X FAR 36 Characteristic Group Absorption of Organic Molecules 85 E CHz=C-CH=CHa nomENE cy am co SeSIadE UR arm qt Wiavelength, (am) como cut ma 2s 3 4 5 7 82 9 tw 2 15 o 30 40 ao 1 , Lulu sis Aga LL LL sad a 005 1 0.10 q 8 ax + E E E 080 4 5 É 040] 1 q 0.50 q 280 4 os E q 10 3 4 QL LL Ls a A A a ts Lato 14v 4 Ad * 4000 3500 3000 2500 2000 1800 1860 1400 1200 1000 ER ato 200 WAVENUMBERS (cm!) FIGURE 3.11. Isoprene. A. The CH stretch: =C—H 3090 em! B. Coupled C=€C—C=<c stretch: symmetric 1640 em! (weak), asymmetric 1598 em! (strong). €. The C—H bend (saturated, alkene in-plane). D. The C—H out-o£-plane bend: 990 cm !, 892 em! (see vinyl, Appendix Table D-1.) Conjugation ot an alkene double bond with an ar- 36.43 Alkene C—H Bending Vibrations Alkene omatic ring produces enhanced alkene absorption near C—H bonds can undergo bending cither in the same 1625 em! The absorption frequency of the alkene bond in conjugation with a carbonyl group is lowered by about 30 em *; the intensity of absorption is increased. In s-cis structures, the alkene absorption may be as intensc as that of the carbonyl group. s-Trans structures absorb more weakly than s-cis structures. Cumulated Alkenes A cumulated double-bond system, as occurs im the allenes (2e-e-en,) ab- sorbs near 2000-1900 em”, The absorption results from asymmetric C=C==C stretching. The absorption may be considered an extreme case of exocyclic C=C ab- sorption. 3.6.4.2 Alkene C—H Stretching Vibrations In gen- eral, any C—H stretching bands above 3000 cm”! result from aromatic, heteroaromatic, alkyne, or alkene C—H stretching. Also found in the same region are the C—H stretching in small rings, such as cyclopropane, and the C—H in halogenated alkyl groups. The fre- quency and intensity of alkenc C—H stretching ab- sorption are influenced by the pattern of substitution. With proper resolution, multiple bands are observed for structures in which stretching interaction may occur. For example, the vinyl group produces three closely spaced C—H stretching hands. Two of these result from sym- metrical and asymmetrical stretching of the terminal C—H groups, and the third from the stretching of the remaining single C—H. plane as the C=C bond or perpendicular to it; the bending vibrations can be either in phase or out of phase with respect to each other. Assignments have been made for a few of the more prominent and reliable in-plane bending vibrations. The vinyl group absorbs near 1416 cm! because of a scis- soring vibration of the terminal methylene. The C—H rocking vibration ot a cis-disubstituted alkene oceurs in the same gencral region. The most characteristic vibrational modes of al- kenes are the out-of-plane C—H bending vibrations betwcen 1000 and 650 em-!, These bands are usually the strongest in the spectra of alkenes. The most reliable bands are those of the vinyl group, the vinylidene group, and the trans-disubstituted alkene. Alkene absorption is summarized in Appendix Tables D-1 and D-2. Im allene structures, strong absorption is observed near 850 em, arising from =CH, wagging. The first avertone of this hand may also be seen. Some spcc- tra showing alkene features are shown in Appendix B: trichlorocthylene (No. 12) and tetrachloroethylene (No. 13). 3.6.5 Alkynes The two stretching vibrations in alkynes (acetylencs) in- volve C=C and C—H stretching. Absorption due to C—H bending is characleristic of acetytene and monosubstituted alkynes. The spectrum of Figure 3.12 is that of a typical terminal alkyne, 3.6.5.1 C=€ Stretching Vibrations The weak C=C stretching band of alkyne molecules occurs in the region 86 Chapicr3 Infrared Spectrometry dor1s NM T, 2.949A 33106 14864 1249.7 Fp er 29606 13798 7398 nB 1.3974 21180 13270 6800 Wavelengih, (um) 244422 CAS [693027] Ew8215 1-Hexyne, 99% He=c(cH,) cu, mp -132ºG bp71-72ºC mo tt 20 4 Ap 20 ap asas BOM E nº tapes, mm pm ra, ay º pi ni o k as 8 a z É NEAT i | ai o da amo si sed suomi mo ii "oo “amo WAVENUMBERS (om —1) FIGURE 3.12, 1-lcexyne. A, The =C—II stretch, 3310 em 1. B. Alkvl € (sec Fig. 3.8), 2857- 2941 em 1. C. The C==C stretch, 2119 em ?, D. The —H bend fundamental, 630 cm. overtone, 1250 em]. E. The == of 2260-2100 em-!. Because of symmetry, no C==€ band is observed in the IR for symmetrically substituted alkynes, in the TR spectra of monosubstituted alkynes, the band appears at 2140-2100 cm-!, Disubstituted al- kynes, in which the substituents are different, absorb near 2260-2190 em-!. When the substituents are similar in mass, or produce similar inductive and resonance ef- fects, the band may be so weak as to be unobserved in the IR spectrum. For reasons of symmetry, a terminal €=€ produces a stronger band than an internal € (pseudosymmetry). The intensity of the C==C stretching band is increased by conjugation with a carbonyl group. 36.52 CH Stretching Vibrations The C—H stretching band of monosubslituted alkynes occurs in the general region of 3333-3267 cem”). This is a strong, band and is narrower than the hydrogen-bonded OH and NJI bands occurring in the same region. 3.6.5.3 C—H Bending Vibrations The C—H hend- ing vibration of alkynes or monosubstituted alkynes leads to strong, broad abscrption in the 700-610 em”! region. The first overtone of the €C—H bending vibra- tion appears as a weak, broad band in the 1370- 1220 em”! region. 3.6.6 Mononuclear Aromatic Hydrocarbons The most prominent and most informative bands in the spectra of aromalic compounds occur in the low- frequency range between 900 and 675 emm!. These strong absorption bands result from the out-of-planc Coop”) bending of the ring C—H bonds. In-plane bending bands appear in the 1300-1000 em”! region. Skeletal vibrations, involving carbon-carbon stretching, ipi, ER RR RA RR ARO A AIN Eno 1 Ny Ps , dão “da NIGOLET 208X FTIR —MH stretch H bend within lhe ring, absorb in the 1600-1585 and 1500- 1400 em! regions. The skeletal bands frequently appear as doublets, depending on the nature of the ring sub- stituents. Aromatic C—H stretching bands occur between 3100 and 3000 em !. Wcak combination and evertonc bands appear in the 2000-1650 em ! region. The pattern of the avertone bands is not a reliable guide to the substitution pattern of the ring. Because they are weak, the overtonc and combination bands are most readily observed in spectra obtained from thick samples. [he spectrum of Figure 3,13 is that of a typical aromatic (benzenoid) compound. 3.6.6.1 Qut-of-Plane C—IN Bending Vibrations The in-phase, out-of-planc bending of a ring hydrogen atom is strongly coupled to adjacent hydrogen atoms, The po- sition of absorption of the out-of-plane bending bands is therefore characteristic of the number of adjacent hy- drogen atoms on the ring. The bands are frequentiy in- tense and appear at 900-675 em !. Assignments Lor €— E out-of-plane bending bands in the spectra of substituted benzenes appear in the chart of characteristic group absorptions (Appendix C). Thesc assignments are usually reliable [or alkyl-substi- tuted benzenes, but caution must be observed in the interpretation of spectra when polar groups are al- tached directly to the ring. for example, im nitroben- zenes, aromatic acids, and esters or amides of aromatic acids. The absorption band that frequently appears in the spectra of substituted benzenes near 600-420 cm ! is attributed 10 out-of-plane ring bending. Some spectra showing typical aromatic absorption appear in Appen- dix B: benzene (No. 4), indene (No. 8), diethylphthalate (No. 21), and sm-xylene (No. 6). 36 Characteristic Group Absorptions of Organic Molecules 87 X1040 CAS [95-47-6] CH; FW 108.17 dos 1R II, 584D 29596 19838 085.1 o-Xylene, 97% e mp-23ºC Fp90oer NMR II, 1,740B 1605.7 11196 741.3 Ha bp 143-145ºC ng 1.5048 Merck 10,9890 1495.2 10525 505.3 Wavalength, (um) mê PU pisa as 4 as 2 A E DE RR E Main : a, Ano APUA o ses E as RIO fi Nf Tape Lê ! 4 BE Led ea fe ! | | | “a. À ER proa É H a pi + ali Ei | a | NEAT | vt “F. de a a do bo dd dd São ado” ico zo 200 Emo tão | umo o cone mo! º WAVENUMBERS (cn!) mo “o NICOLET 208X FTIR FIGURE 3.13. o-Xylene. A. Aromatic C—H stretch, 3008 cm-t B. Methyl C—H stretch, 2965, 2940, 2918. 2875 em”! (see Fig. 3.8). €. Overtone or combination bands, 2000-1667 em ! (see Fig. 3,14). D. The In-plane C—H bend, 1052, 1022 em “1. F, Out-of-plan ot-plane ring C==C bend, 438 em. 3.6.7 Polynuclear Aromatic Hydrocarbons Polynuclear aromatic compounds, like the mononuclear aromatics. show characteristic absorption in three regions of the spectrum. The aromatic C—H stretching and the skeletal vi- brations absorb in the same regions as observed for the mononuclear aromatics. The most characteristic absorp- tion of polynuclear aromatics results from C—H out- of-planc bending in the 900-675-cm-! region. These bands can be correlated with the number of adjacent hydrogen atoms on the rings. Most 8-substituted nuph- thalenes, for example, show three absorption bands re- sulting from out-of-plane C—H bending; these corre- spond to an isolated hydrogen atom and two adjacent hydragen atoms on one ring and four adjacenthydrogen atoms on the ather ring. In the spectra of «-substituted naphthalenes the bands for thc isolated hydrogen and the two adjacent hydrogen atoms of B-naphthalenes are replaced by a band for three adjacent hydrogen atoms. This band is near 810-785 emrt, CH Out-of-Planc Bending Vibrations ota f-Suhstituted Naphthalene Substitution Pattern Isolated hydrogen 862-835 Two adjacent hydrogen atoms 83s 805 Four adjacent hydrogen atoms 760-735 Cring stretch, 1605, 1495, 1466 em-!. F. C—H bend, 744 em |. G. Oul- Additional bands may appear because of ring bend- ing vibrations. The position of absorption bands for more highly substitutcd naphthalenes and other poly- nuclear aromatics are summarized by Colthup et al. (1990) and by Conley (1972). 3.6.8 Alcohols and Phenols The charactcristic bands observed in the spectra of al- cohols and phenols result from O—H stretching and C—O stretching. These vibrations are sensitive to hy- drogen honding. The C—O stretching and O—H bending modes are not independent vibrational modes because they couple with the vibrations of adjacent groups. Some typical spectra of alcohols and a phenol arc shown in Figures 3.14-3.16. 36.81 O—H Stretching Vibrations Thc non- hydrogen-bonded or “free” hydroxyl group of alcohols and phenols absorbs strongly in the 3700 — 3584 em ! region. Lhesc sharp, “free” hydroxyl bands are ob- served in the vapor phase, in very dilute solution in non- polar solvents or for hindered OH groups. Intermolee- ular hydrogen bonding increases as the concentration of the solution increases, and additional bands start to ap- pear at lower frequencies, 3550-3200 em !. at Lhe cx- pense of the “free” hydroxyl band, This effect is illus- trated in Figure 3.17, in which lhe absorption bands in the Q—H stretching region are shown for two dillerent concentrations of cyclohexylcarbinol im carbon tetra- chloride. For comparisons of this type, the path length of the cell must be altered with changing concentration, so that the same number of absorbing molecules will be present in thc TR beam at cach concentration. The band at 3623 em”! results from the monomer, whereas the 90 Chapter3 Infrared Spectrometry 36.82 C—O Stretching Vibrations The C—O stretching vibrations in alcohols and phenols produce a strong band in the 1260-1000 em”! region of the spec- trum. The C—O stretching mode is conpled with the adjacent C—C stretching vibration; thus in primary al- cohols the vibration might better be described as an asymmetric C—C—O stretching vibration. The vibra- tional mode is further complicated by branching and «,B-unsaturation. These effects are summarized as fol- lows for a series of secondary alcohols (neal samples): Secondary Alenhok Abserption (em!) 2-Butanol 1105 3-Methyl-2-butano! 1091 1-Phenylethanol 1073 3-Buten-2-0] 1058 Diphenylmethanol 1014 The absorption ranges of the various types of al- cohols appear in Table 3.2, below. These values are for neat samples of the alcohols. Mulls, pellets, or melts of phenols absorb at 1390- 1330 and 1260-1180 cm-!. These bands apparentiy result from interaction between O—H bending and €—O stretching. The long-wavelength band is the stronger and both bands appear at longer wavelengths in spectra observed in solution. The spectrum of Figure 3.16 was determined on a meit. to show a high degree of association. 3.683 OH Bending Vibrations The O—H in- plane bending vibration occurs in lhe gencral region of 1420-1330 em"! In primary and secondary alcohols, Table 3.2 Alcoholic C—O Stretch Absorptions the O—H in-plane bending couples with the C—H wagging vibrations to produce two bands; the first near 1420 em, the second near 1330 em |, These bands arc of little diagnostic value. Tertiary alcohols, in which no coupling can occur, show a single band in this region, the position depending on the degree of hydro- gen bonding. “The spectra of alcohols and phenols determined in the liquid state, show a broad absorption band in the 769-650 em ! region because of out-of-plane bending of the bonded O—H group. Some spectra showing typ- ical alcoholic absorptions are shown in Appendix B: ethyl alcohol (No. 16) and methanol (No. 15). 3.6.9 Ethers, Epoxides, and Peroxides 36941 C—O Stretching Vibrations The character- istic response of ethers in the IR is associated with the stretching vibration of the C—O—C system. Since the vibrational characteristics of this system would not be expected to differ greatly from the C—C—C system, it is not surprising to find the response to C—O—C stretching in the same general region. However, since vibrations involving oxygen atoms result in greater di- pole moment changes than those involving carbon at- oms, more intense TR bands are observed for cihers. The €C— OC stretching bands of ethers, as is the case with the C—O srretching bands of alcohols, involve coupling with other vibrations within the molecule. The spectrum of Figure 3.19 is that of a typical aryl alkyl ether. In addition, the specira of ethyl ether (No. 22) and p-dioxane (a cyclic diether, No. 23) are shown in Appendix B. In the spectra of aliphatic ethers, the most char- Alcohol Type Alsarption Range (em-!) (1) Saturated tertiary so (2) Secondary. highly symmetrical | 1205-1124 (1) Saturated secondary o (2) a-Unsalurated or cydlie ter. 1124-1087 (1) Secondary, a-unsaturated (2) Secondasy. alicyelie five- ar six-membered ring 1085 «1054 (3) Saturated primary (1) Tertiary. highly a-unsaturated (2) Secondary, di-a-unsaturated (3) Secondary, «-unsaturated and «-branched <1050 (4) Secandary, alicyclic seven- or eight-membered ring (5) Primary, a-unsalurated and/or a-brancheg 36 Characteristic Group Absorptions of Organic Molecules 91 ocu, 123228 castrooeesa (O) Fw 108.14 40.995 IR II, 244 16009 12473 7841 Anisolo, 99%. mp 37ºC Fp125ºF NMR E, 1,833A 14979 11726 7544 bp 154ºG nB £.5160 Merck 10,691 13030 10405 6920 Wavelengt, (am) 22 2 mA as doar anaa Ec, ss RA mo Ê EE ME E sá io WAVENUMBERS (on!) NICOLET 205X FTAR FIGURE 3.19. Anisole. A. Aromatic C—H stretch, 3060, 3030, 3000 em-! B. Methyl C—H stretch, 2950, 2835 em-!. €. Overtane-combination region, 2000-1650 em-!. D. The C= ring stretch, 1600, 1498 cm |. E. Asymmetric C—O—C stretch, 1247 em ".F. Symmetric C—O—C stretch, 1040 em ?. G. Out-of-planc C—H bend, 784, 754 cm !.H. Out-of-plane ring C=C bend, 692 em |. aeteristic absorption is a strong band in the 1150- 1085 em” region because of asymmetrical C—O—C To stretching; this band usually occurs near 1125 em". The trans — 1620 em ! symmetrical stretching band is usually weak and is more readily observed in the Raman spectrum. The C—O—C group in a six-membered ring ab- sorbs at the same frequency as in an acyclic ether. As the ring becomes smaller, the asymmetrical €C—O—C stretching vibralion moves progressively to lower wavenumbers (longer wavelengths), whereas the sym- metrical C—O —€ stretching vibration (ring breathing frequency) moves to higher wavenumbers. Branching on the carbon atoms adjacent to the oxy- gen usually Icads to splitting of the C—O—C band. Isoprops] ether shows a triplet structure im the 1170- 1114-cm ! region, the principal band occurring al Wi4em, Spectra of aryl alkyl cthers display an asymmetrical C—0—C siretching band at 1275-1200 em with symmetrical stretching near 1075 - 1020 cm”! Strong ab- sorption caused hy asymmetrical C—O —C stretching in vinyl ethers occurs in the 1225-1200 em! region with H E a strong symmetrical band at 1075-1020 cm !. Reso- l A nanec, which results in strengthening of the C—O R=0-€=E bond, is responsible for lhe shift in the asymmetric ab- H sorption band of arylalkyl and vinyl ethers. terminal CJ, wag, SE3 em” The C=C stretching baná of vinyl ethers occurs in trans CH wag, 960 cm” the 1560-1610 em ! region. This alkene band is char- acterized by its higher intensity compared with the Alkyl and aryl peroxides display €- C—O ub- C—C stretching band in alkenes. "his band frequently sorption in Lhe 1198-1176 em” region. Acyl and aroyl appears as a doublet resulting from absorption of rota- peroxídes display two carbeny] absorption bands in the lional isomers. 1818-1754 em ! region. Iwo bands are observed bu- cis 1640 em! Coplanarity in the trans isomer allows maximum resonance, thus more etfectively reducing the double- bond character of the alkene linkage. Steric hindrance reduces resonance in the cis isomer. The two bands arising from =C—H wagging in terminal alkenes occur near 1000 and 909 cm-!. In the spectra of vinyl elhers, thesc bands are shifted to longer wavelengths because of resonance, 1 92 Chapter3 Infrared Spectrometry cause of mechanical interaction between the stretehing modes of the two carbonyl groups. The symmetrical stretching, or ring breathing fre- quency, of the epoxy ring, all ring bonds stretching and contracting in phasc, occurs near 1250 cm-!. Another band appears in the 950-810 em ! region attributed to asymmetrical ring stretching in which the C—C bond is stretching during contraction of the C—O bond. A third band, referred to as the “12 micron band,” appears in the 840750 cm | region, The CH stretching vi- brations of epoxy rings oceur in the 3050-2990 cm! region of the spectrum. 36.10 Ketones 36.101 C=0 Stretching Vibrations Ketones, alde- hydes, carboxylic acids, carboxylic esters, lactones, acid halides, anhydrides, amides, and lactams show a strong €C=o0 stretching absorption band in the region of 1870- 1540 cm. Tts relatively constant position, high inten- sity, and relative freedom from intertering bands make this onc of the easiest bands to recognize in IR spectra. Within its given range, the position of the C=0 stretching band is determined by the following factors: (1) the physical state, (2) electronic and mass clfects of neighboring substituents, (3) conjugation, (4) hydro- gen bonding (intermolecular and intramolecular), and (5) ring strain. Consideration of these factors leads to a considerable amount of information about the environ- ment of the C==O group. In a discussion of these effects, it is customary to refer to the absorption frequency of a ncat sample of a saturated aliphatic ketonc, 1715 cm ?, as “normal.” For example, acetone and cyclohexanone absorb at PBIOS CAS(107879] q Fwss13 2Pentanone, 97% cm, EcHCHCH, mp-7850 ba 190-1019C | tida tl ER do do” ido 200 300 nos “ia SE ai oo ai dio 25 WAVENUMBERS (cm!) Wavelength, (am) Mt 1715 em-!. Changes in the environment of the carbony] can cilher lower or raise the absorption frequency from this “normal” value. A typical ketone spectrum is dis- played in Figure 3.20. The absorption frequency observed for a neat sam- ple is increased when absorption is observed in nonpo- lar solvents. Polar solvents reduce the frequency of ab- sorption. The overall range of solvent effects does not exceed 25 em 1. Replacement of an alkyl group of a saturated ali- phatic ketone by a hetero atom (G) shifts the carbonyl absorption. The direction of the shift depends on whether the inductive effect (a) or resonance effect (b) predominates, Gs Ro. A =0 EO R R (a) (b) The inductive effect reduces the length of the €=0 bond and thus increases its force constant and lhe frequency of absorption. The resonance effect in- creases the €C=0 bond length and reduces the fre- quency of absorption. The absorptions of several carbonyl compound classes are summarized in Table 3.3. Conjugation with a C==C bond results in delocali- zation of the 7 electrons of both unsaturatcd groups. Delocalization of the 7 clectrons of the C=O group reduces the double-bond character of the C—O bond, causing absorption at lower wavenumbers (longer wavelengths). Conjugation with an alkene or phenyl group causes absorption in the 1685-1666 cm ! region. Additional conjugation may cause a slight further re- dos IR, 240D 20630 13660 1707 Fp4ser NMA IL, 1,369C 17174 12055 7270 nB 1.3897 Merck 10,5988 14229 12355 5919 1 4 Ve AR a REP “io do NIGOLET 208X FTIR FIGURE 3.20, 2-Pentanone. A, v,, Methyl, 2964 em"! B. »,, Methylene, 2935 em. C. 4, Methy], 2870 em !. D. Normal C=0O stretch, 1717 em-t. E. à. CH,, —1423em 1.F. 8, CH,, — 1410 cm-!. G. &, CH; of CH,CO unit, 1366 em-!. H. The C—CO—C stretch and bend, 7l em !. 36 Characteristic Group Absarptions of Organic Molecules 241369 CAS (34713-70-7] á Fw 134.18 (£)-2-Phenyiproplonaldehyde, 98% (O) bp S4ºCH2mm d1.011 95 Fp 169ºF NMRI 21018 29779 14920 7596 nB 1.5176 17242 10211 7003 180168 8648 5251 Wavelength, (um) a ' PRA A COTA o nr 1 j »04 ni] J I ie mil sa à A É ai “8 4 : apo . i : E A Eroa »á Vl tas a ; ias - t 17 w NEAT E | nel a id bão dao cão co do dio do dO “dy Sd 005 250 El ae UE ato - E WAVENUMBERS (em 1) GURE 3.22. (+)-2-Phenylpropionaldenyde. * Aromatic, 3070, 3040 cm”! (see Fig. 3.13). B.* Aliphatic, 2978, 2940, 2875 cm: (see Figs. 3.8 and 3,13). C* Aldehydic, C—H stretch, 2825, 2720 em !, Doublet from Fermi resonanee wilh overtone of band at F. D. Normal aldehydic C==0 stretch, 1724 em *. Conjugated O stretch would be about 1700 cmo, for example, as for C,H;CHO. E. Ring C==€ stretch, 1602, 1493, 1455 cmi. F. Aldehydic C—H bend, 1390 em. G. Out-ol-plane C—H bend, 760 em-!. H. OQut-of- plane C==C bend. 700 em '. *Bands A—C are CL stretch absorptions Source: Courtesy of Aldrich Chemical Company. Some aromatic aldehydes with strongly electroncg- ative groups in the oriho position may absorb as high as 2900 em !. An absorption of medium intensity near 2720 cm !, accompanied by a carbonyl absorption band is good ev- idence for the presence ot an aldehyde group. 3.6.12 Carboxviic Acids the ionic resonance structure. Because of the strong bonding, a rec hydroxy) stretching vibration (near 3520 em-!) is observed only in very dilute solution in nonpolar solvents or in the vapor phase. Carboxylic acid dimers display very broad., intense OH stretching absorption in the region of 3300- 2500 em", The band usually centers near 3000 em. The woaker C—H stretching bands are generally seen eunarimnnced unan the hroad O-—H band. Fine struc- 96 Chapter3 Infrared Spectrometry 146870 CAS[IIIISE] o Fw 13019 dog IR TI 2846 31560 1710.7 12847 Heptanolc acid, 95%. h mp 10.50 Fp >235ºF NMA IL 1,420C 28318 14675 12075 cn(ch;) Com dp 223-222.5ºC nb t422t Merck 10,4552 D766 14133 g985 Wavelength, (um) ' 7 £ AMME E 2 !ootiiandado | É “a Moju, cin jeito anais Lo das TS Dia ia DE / Po Nitiiiia dedo “é iii” nodo “Bi 3000 Sida 3206 Só ádco ab ido BaG5 TAS add ama SO Trad TD do ão do NICOLET 205X FR WAVENUMBERS (cm *) FIGURE 323, Heptanoic acid. A. Broad O—H stretch, 3300-2500 em-!, B. The C—H stretch (see Fig. 3.8), 2950, 2932, 2855 cm *. Supcrimposed upon O—H stretch. €. Normal, dimeric carboxylic C=0 stretch, 1711 em!. D. The C—O—H in-plane bend,* 1413 cm. E. The C—O stretch,* dimer, 1285 em ?. F. "he O—1I out-of-plane bend, 939 cm. *Bands at D and E involve C—O — H interaction. 36.122 C—O0 Siretching Vibrations The C=0 the conformation in which the halogen is in proximity stretching bands of acids are considerably more intense to the carbony! group. than ketonie C==0O stretching bands. The monomers of saturated aliphatic acids absorb near 1760 cm”. The carboxylic dimer has a center of symmetry; only the asymmetrical O stretching mode absorbs in the IR. Hydrogen bonding and resonance weaken the €=0O bond, resulting in absorption al a lower fre- 36.123 C-—O Stretching and O-—H Bending Vibrations Two bands arising from C—O stretching and O—H bending appear in the spectra of carboxylic quency than the monomer. The C=O group in dimer- acids near 1320-1210 and 1440-1395 em, Tespec- ized saturated ahphatie acids absorbs in the region of tively. Both of these hands involve some interaction be- 1720-1706 em |. tween C—O stretching and in-plane C—O—H bend- ing. The more intense band, near 1315-1280 em”! for dimers, is generally referred to as the C—O stretching band and usually appears as a doublet in the spectra of long-chain fatty acids. The C—-O—H bending band near 1440-1395 cm”! is of moderate intensity and oc- curs in the same region as the CH, scissoring vibration of the CH, group adjacent to the carbonyl. One of the characteristic bands in the spectra of dimeric carboxylic acids results from the out-of-plane bending of the bonded O—H. The band appears near 920 cm”! and is characteristically broad with medium intensity. Internal hydrogen bonding reduces the frequency of the carbonyl stretching absorption to a greater degree than does intermolecular hydrogen bonding. For ex- ample, salicylic acid absorbs at 1665 cm !, whereas p-hydroxybenzoic acid absorbs at 1680 em !. Unsaturation in conjugation with the carboxylic carbonyl group decrcases the frequency (increases the wavelength) of absorption of both the monomer and dimer forms only slightly. In general, «,B-unsaturated and aryl conjugated acids show absorption Jor the dimer in the 1710-1680 em ! region, Extension of conjugation beyond the «,8-position results in very little additional shifting of the C=0O absorption. Substitution in the a-position with electroncgalive groups, such as lhe halogens, brings about a slight in- crease in the € absorption frequency (10-20 em-", 3.6.13 Carboxylate Anion The spectra of acids with halogens in the a-position, determined in the liquid state or in solution, show dual “The carboxylate anion has two strongly coupled C="O0 carbonyl bands resulting from rotational isomerism bonds with bond strengths intermediate between C=O (ficld elfect). The higher frequency band corresponds to and C—O, 36 Characteristic Group Absorptions of Organic Molecules The carboxylate ion gives rise to two bands: a strong asymmetrical stretching band near 1650-1550 em”! and a weaker, symmetricai stretching band near 1400 cm", “The conversion of a carboxylic acid to a salt can serve as confirmation of the acid structure. This is con- veniently done by the addition of a tertiary aliphatic aminc, such as triethylamine, 10 a solution of the car- boxylic acid in chloroform (no reaction occurs in CCI). The carboxylate ion thus formed shows the two char- acteristic carbonyl absorption bands in addition to an “ammonium” band in the 2700-2200 cm | region. The O—H stretching band, of course, disappears. The spec- trum of ammonium benzoate, Figure 3.24, demonstrates most ol these features. 3.6.14 Esters and Lactones Esters and lactones have two characteristically strong absorption bands arising from C=0 and C—O stretching. The intense C=0 stretching vibralion oc- curs at higher frequencies (shorter wavelength) than that of normal ketones. Lhe force constant of the car- bonyl bond is increased by the electron-attracting na- ture of the adjacent oxygen atom (inductive effect). Overlapping occurs between esters in which the car- bonyl frequency is lowered, and ketones in which the 1 ago paul 005 aro ES aso ao TTTTT 97 normal ketone frequency is raised. A distinguishing feature of esters and lactones, however. is the strong C—O stretching band in the region where a weaker band occurs for ketones. There is overlapping in the €=0 frequency of esters or lactones and acids, but the OH stretching and bending vibrations and the possibil- ity of salt formation distinguish the acids. The frequency of the ester carbonyl responds to en- vironmental changes in the vicinity of the carbonyl group in much the same manner as ketones. The spec- trum of phenyl acetate, Figure 3.25, illustrates most of the important absorption characteristics for esters. 36.141 C=0 Stretching Vibrations The C=0 ab- sorption band of saturated aliphatic esters (except for- mates) is in the 1750-1735 cm”! region. The C=O absorption bands of formates, «,B-unsaturated, and benzoate esters are in the region of 1730-1715 em". Further conjugation has little or no additional effect upon the frequency of the carbonyl absorption. In the spectra of vinyl or phenyl esters, with unsat- uration adjacent to the C—O— group, a marked rise in the carbonyl frequency is observed along with a low- cring of the C—O frequency. Vinyl acetate has a car- bonyl band at 1776 em-!; phenyl acetate absorbs at 1770 emt. «-Halogen substitution results in a rise in the €=o0 stretching trequency. Ethyl trichloroacetate ab- sorbs at 1770 em-!. In oxalates and a-keto esters, as in a-diketones, there appears to be little or no interaction between the two carbony groups so that normal absorption occurs CAMOND; MM ÍIDIS MP (88-UDPC Dr Mater Wavelength, (am) 7 8 9 m 12 15 2 m so para Logs ris oria tosa rm titulo ago A 1190 e Ve o 4 200 asas its ds = 4000 3500 3000 2500 2000 1800 1800 1400 1200 1000 80 800 400 200 FREQUENCY (em?) SCANNED ON PERKIN-ELHER 571 FIGURE 3.24. Benzoic acid, ammonium salt. A, N—H and C—H stretch, 3600- 2500 emr1. B. Ring C==C stretch, 1600 em !. stretch, 1550 cm-!, D. Symmetric carboxylate C( Asymmetric carboxylate anion C(=0); =0) streich, 1385 em!.