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ch22_solutions - CHAPTER 22 SUPPLEMENTARY SOLUTIONS MASS...

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CHAPTER 22: SUPPLEMENTARY SOLUTIONS 105 MASS SPECTROMETRY S22-1. (a) The peak at m/z 71 is C 4 H 7 O + . Its contribution to m/z 72 should be Intensity = 4 u 1.08% + 7 u 0.012% + 1 u 0.038% = 4.4% of m/z 71 13 C 2 H 17 O The observed intensity of 4.9% in spectrum ( a ) is reasonable, but the 10.7% intensity in spectrum ( b ) is too great. There is probably another contribution to the m/z 72 peak in spectrum ( b ). (b) The extra intensity in the peak at m/z 72 in represents loss of a neutral molecule with a mass of 28 Da from the molecular ion. The McLafferty rearrangement can split C 2 H 4 from 3-hexanone, but not from 2-methyl-3-pentanone, which lacks a J -CH group. O C CH 2 CH 3 H O C CH 2 CH 3 H 2 C CH 2 CH 2 H Ethylene 28 Da McLafferty rearrangement J + D E m/z = 72 3-Hexanone S22-2. 12 C abundance . a = 0.989 3 13 C abundance . b = 0.010 7 Abundance of 12 C 3 H 6 = a 3 = 0.968 2 Abundance of 12 C 2 13 CH 6 = 3 a 2 b = 0.031 4 2 Abundance of 12 C 13 C 2 H 6 = 3 ab 2 = 0.000 339 8 Abundance of 13 C 3 H 6 = b 3 = 0.000 001 22 5 Relative abundances: M + : M+1 : M+2 : M+3 = 1 : 0.032 4 : 0.000 351 : 0.000 001 27 S22-3. (a)
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