1. Mechanism of Phenylurethane
1-butanol and phenyl isocyanate

2. Mass Spectrometry Interpretation of Mass Spectra
Check 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

3. 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

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

5. Isotope Peaks: 35Cl and 37Cl

6. Isotope Peaks: 79Br and 81Br

7. Molecular Ion Peak: Alcohols …
1-butanol

8. 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

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

10. Fragmentation of alkanes

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

12. Fragmentation in Aromatics Tropylium Ion

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

14. Acyl Fragment
acetophenone

15. Characteristic 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!)

16. Weights of common fragments or neutral losses

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

18. 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