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Lecture 23

Lecture 23. Quiz 6 Average = 72% (36 out of 50) Mass Spectrometry This week in lab: Ch 9 Final Report Due Synthetic #2 PreLab Due Next week in lab: Synthetic #1 Final Report Due. Molecular Ions.

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Lecture 23

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  1. Lecture 23 Quiz 6 Average = 72% (36 out of 50) Mass Spectrometry This week in lab: • Ch 9 Final Report Due • Synthetic #2 PreLab Due Next week in lab: • Synthetic #1 Final Report Due

  2. Molecular Ions Molecular Ions = sum of atomic weight(s) of all isotopes of all elements in a molecule. If you had 10,000 atoms of each type: • C: 9890 12C atoms 110 13C atoms • H: 9999 1H atoms 1 2H atoms • O: 9985 16O atoms, 4 17O atoms, 20 18O atoms • N: 9963 14N atoms 37 15N atoms • Cl: 7577 35Cl atoms 2423 37Cl atoms (3:1 35Cl:37Cl) • Br: 5069 79Br atoms 4931 81Br atoms (1:1 79Br:81Br)

  3. Molecular Ions: Cl & Br Compounds - Isotopes Significant M+2 peak => Cl or Br • Cl is 3 parts 35Cl and 1 part 37Cl • Br is 1:1 79Br and 81Br

  4. MS of Chlorobenzene M+ C6H535Cl =m/z 112 C6H537Cl = m/z 114 Note ratio: m/z 112:114 is 3:1 M + 2

  5. MS of Bromobenzene C6H579Br = m/z 156 C6H581Br = m/z 158 M+ = 156 M + 2 = 158 Note ratio: 156:158 1:1

  6. Mass Spec Correlation Chart #1 Common fragments ions and/or neutral losses: • 15 can only be methyl • 17 usually OH • 18 always H2O • 28 CO or CH2=CH2 • 29 CH3CH2 or CHO • 31 CH3O • 35/37 Cl (special isotope pattern too!) • 42 CH2=C=O • 43 CH3CO or C3H7 • 45 CH3CH2O or COOH • 79/81 Br (special isotope pattern too!)

  7. Mass Spec Correlation Chart #2 Weights of common fragments or neutral losses:

  8. Lab Guide Problems Problem 15.3 Mass spec shown in class (Figure 15.11) Account for the peaks at m/z values of 88 (M+) , 73, 70, 59, and 55.

  9. Lab Guide Problems Problem 15.5 Account for the peaks in the mass spectrum of 2-octanone at m/z values of 129 (M+1), 128 (M+), 113, 85, and 43.

  10. Lab Guide Problems Problem 19.13 The most intense peak in the mass spectrum of 2,2-dimethylbutane is at m/z = 57. Propose a structure of this fragment ion (a.k.a. daughter ion).

  11. Nutmeg Oil GC-MS Data Mass Spectrum of A M+ at 192 Compound is:

  12. Nutmeg Oil GC-MS Data Mass Spectrum of B M+ at 208 Compound is:

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