1. Complete this reaction equation:
MiniQuiz 8 Problem:
Complete this reaction equation: NH 2 OH NO O N +

2. Following Tuesday (May 12):
Today:
Mass Spectrometry
Next time:
H-NMR, CMR
Following Tuesday (May 12):
Your questions
Final Exam in Lab

3. Mass Spectrometry Interpretation of Mass Spectra
Study Mass Spectrometry Chapters in
Lab and Lecture Texts
Molecules of a sample are bombarded by a stream of high energy electrons
Molecular ion peak M+.
Molecular ion bonds break to give fragment IONS and NEUTRAL radicals or molecules. Mass Spectra only show ions, not neutrals.
m/z of M+ - m/z of F+ (fragment ion) = mass of neutral
Each peak can be interpreted in terms of both a fragment ion and/or a neutral loss

4. A Mass Spectrum tells you the molecular mass
Mass Spectrometry
Molecular ion peak (M+.) at m/z 32
Base peak at m/z 31
Fragment ions at 29 and 15
A Mass Spectrum tells you the molecular mass

5. Molecular Ion Peak: Odd or Even Mass?
aniline

6. Isotope Peaks: 35Cl and 37Cl

7. Isotope Peaks: 79Br and 81Br

8. Molecular Ion Peak: Alcohols …
1-butanol
MW: 74

9. Favored Fragmentations
The greater the stability of the fragment ion, the more intense the peak
Alkyl ion stability follows carbocation chemistry rules:
3° and allyl more stable than 2°
2° more stable than 1°
Acyl ions are stable (m/z 43, 57..)
PhC=O+ (m/z 105…)
Alpha (a) cleavage in alcohols, amines, ethers
Aromatic rings do NOT fragment easily

10. Characteristic Fragment Ions
Look for alkyl ions at m/z 43, 57, 71, 85 (14 amu or CH2 series)

11. Fragmentation of alkanes

12. Characteristic Fragment Ions
Look for aryl ions at 77 (phenyl), 91 (benzyl), and 105 (benzoyl)

13. Fragmentation in Aromatics Tropylium Ion

14. Characteristic Fragment Ions
Acyl ions are stable (m/z 43, 57..)

15. Acyl Fragment
acetophenone

16. Characteristic Neutral Losses
1 is H (e.g. from aldehydes)
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!)

17. Weights of common fragments or neutral losses

18. Mass Spectrometry Summary
Molecular weight:
odd-numbered (N ...) ?
isotope peaks (Cl, Br)?
Alcohols …
Recognize typical fragments:
H2O, alkyl, acyl, tropylium ion …

19. Brief Review of Mass Spectroscopy Discussion/Review of H-NMR, CMR
Next time:
Bring Spectra of your Unknown #3!
Brief Review of Mass Spectroscopy
Discussion/Review of H-NMR, CMR

20. Complete this reaction equation:
MiniQuiz Problem:
Complete this reaction equation: NH 2 OH NO O N +