1. Recognition of Molecular Ion
Can use CI to verify (usually not convenient)
Nitrogen rule:
No N present M+ is even
N present M+ is odd
M-15 present? M-18? M-31? M-29?
M-3  M-14 peaks indicate not

2. Nitrogen Rule

3. Spectrum of an Amine

4. Spectrum of an Alcohol

5. M+ present?

6. Recognition of Molecular Ion
Can use CI to verify (usually not convenient)
Nitrogen rule:
No N present M+ is even
N present M+ is odd
M-15 present? M-18? M-31? M-29?
M-3  M-14 peaks indicate not
Go back to slides 3, 4, and 5

7. Deducing molecular formula
For small molecules don’t need HRMS
Use %m+1 to get # of Cs
Use Nitrogen rule
M-18 peak indicates oxygen
Doublet M+ peaks indicate Cl (3:1) and Br (1:1)
Peak at 127 = I
Pek at 77 is phenyl group (C6H5)
M+2 peak = 4-5% indicates S
Deduce molecular formula!

8. Molecular Formula?

9. Molecular Formula?

10. Molecular Formula?
m/z %abund
20.2
1.2

11. Index of Hydrogen Deficiency
Units of Unsaturation = r + db
CnHmXxNyOz
r + db = n – m/2 – x/2 + y/2 + 1

12. Fragmentation of M+
Draw structure of M+ if possible and then draw possible heterolytic cleavages (curved arrows) or homolytic cleavages (fish hooks)
Alternatively, show homolytic or heterolytic cleavage cleavage of the molecule and then remove an electron from one of the fragments.
Fragmentation to give neutral molecule and a radical cation must involve some kind of rearrangement.

14. General Rules
Probablity of bond cleavage depends on stability of fragments produced. (3º > 2º > 1º > CH3) (oxonium > carbocation) (allylic, benzylic > no resonance)
R on cycloalkanes α cleave. Cyclohexenes do retro Diels-Alder.
R on aromatic rings β-cleave to benzylic
Bonds β to heteroatoms cleave
Loss of small stable molecules, H2O, NH3, C2H4, HCN, CO, H2S,etc often occur
Increase branching  decrease M+
Add carbons  decrease M+
Cleave more likely at higher º C
Unsubst cyclic have strong M+ (especially aromatic)
Alkenes cleave to allylic species