Organic Chemistry Semester 1 LABORATORY MANUAL - Moravian ...

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Mass Spectrometry Appendix D2 Part V. Techniques and Theory Analysis of Mass Spectra. Since all of the peaks in the mass spectra on the previous page occur at masses ≥ the molecular mass of the compound, it seems reasonable to explore the possibility that the lower mass peaks may indicate the after being struck by a high energy electron, these two molecules break up and the peaks give us information on pieces of the original molecule. This “fragmentation process” can be represented by the equation below. After the molecule has been struck by the high energy electron and lost an electron it has a single + charge. So if the molecule fragments, one of the resulting pieces will have the + charge (A + ) and the other piece will have no charge (B.). M + . > A + + B. Mass spectrometers are designed to detect only positively charged particles. So, the mass of A + can be determined from a peak in the mass spectrum of M, but the mass of B.is not detected by the mass spectrometer. However, the masses of A + + B. = the mass of M + , so the mass of B. can be determined by subtracting the mass of the detected peak for A + from the mass of the molecular ion (M + ). Thus, the peak at m/z = 31 in the spectrum above arises from the splitting of the molecular ion into an + ion of mass 31 and a neutral radical of mass 57 (M-31). Often the radical is smaller than the ion and can be identified in the molecular structure more easily. Table 2-77 on p. 103 in Padías gives masses of many common neutral radicals and cations formed from molecular ion fragmentations. Exploration of Mass Spectral Fragmentation Patterns. 1. Look carefully at each of the two spectra on D1 and the 7 additional spectra below and on pp. D3 → D4. Considering the structure of the compound, the brief introduction to mass spectrometry on pp. D1 & D2 and in Padías & CGWW, try to identify the ions whose masses are indicated with a number in each mass spectrum and the bond that broke to form each ion. Assume that the most ions are produced by breakage of only one bond in the original structure. For large mass ion peaks, you may need to use the [M + - (ion peak mass)] value to identify the radical first. You will note that there are other peaks "clustered" around the designated peaks. These peaks often arise from loss of hydrogen atoms or other small particles from the major ion. a. Intensity b. m/z Intensity O m/z
c Mass Spectrometry Appendix D3 Part V. Techniques and Theory c. 58 N Intensity 44 72 M + 87 H m/z d. 41 56 Intensity 55 69 M + 84 m/z e. Intensity 29 43 44 57 M + 72 O H m/z f. O Intensity O CH 3 m/z
Page 1 and 2: MORAVIAN COLLEGE CHEMISTRY DEPARTME
Page 3 and 4: 2 Introduction PART V: Appendix A T
Page 5 and 6: Fall 2008 4 Part I. Introduction As
Page 7 and 8: Fall 2008 6 Part I. Introduction As
Page 9 and 10: Fall 2008 8 Part I. Introduction We
Page 11 and 12: Fall 2008 10 Part I. Introduction n
Page 13 and 14: Fall 2008 12 Part I. Introduction r
Page 15 and 16: Fall 2008 14 Part II. Lab Rules and
Page 17 and 18: Fall 2008 16 Part III. Lab Record &
Page 25 and 26: Fall 2008 24 Part IV. Experiments P
Page 27 and 28: Extraction Appendix B1 Part V. Tech
Page 29 and 30: Infrared Spectroscopy Appendix C1 P
Page 37: Mass Spectrometry Appendix D1 Part
Page 41 and 42: Mass Spectrometry Appendix D5 Part
Page 43 and 44: Mass Spectrometry Appendix D7 Part
Page 45 and 46: Nuclear Magnetic Resonance Appendix
Page 65: Nuclear Magnetic Resonance Appendix

Organic Chemistry Semester 1 LABORATORY MANUAL - Moravian ...

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