72
3 Combination Tables
Assignment
Range
Comments
Molecular ion
Aliphatic esters: weak, tendency to protonate
Aliphatic lactones: medium to weak, tendency to protonate
Aromatic esters and lactones: strong
Fragments
[M - RO] +
[M - ROCO] +
Esters
Esters
Lactones: loss of α-substituents (attached to
ether carbon), decarbonylation, for aromatic lactones also double decarbonylation
Rearrangements
Alkene elimination from the alcohol moiety:
O
O
R 2
H
R 1
R 1 CH=CH 2
R 2 COOH
+
+ .
+ .
Elimination of the alcohol side chain with
double H transfer (for alcohols with C n≥2 ):
R 1 COOR 2
R 1
OH
OH
+
+ .
Alcohol elimination from ortho-substituted
aromatic esters:
X
H
O
OR
- R O H
X
C
O
for X : CH 2 ,
O ,
N ,
S, etc.
+ .
+ .
[M-18] +·
Lactones
n π*
<220 nm (log ε 1–2)
Aliphatic esters
≥193 nm (log ε ≈4)
α,β-Unsaturated esters
≥230 nm (log ε >3)
Aromatic esters
MS
UV