N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
428
8 Mass Spectrometry
Lactams
Fragmentation: Cleavage of the C–C bond at the N-bearing C atom. Cleavage of
the CO–N bond, followed by loss of CO (Δm 28) or by further cleavage of the
C–C bond next to N, giving an iminium ion. In 2-pyrrolidone and 2-piperidone, the
signal at m/z 30 ([CH 2 =NH 2 ] + ) is strong. The base peak of 2-pyridone is formed by
CO elimination (Δm 28).
2-Pyrrolidone:
N
H
O
N
H
O
H
CH 2
.
CH 2 =N H 2
m /z 30
+
C 3 H 6
+ . m /z 42
C 3 H 5
+
m/z 41
– H
.
– HN CO
N
H +
N
. C
O
H
O
N
C
CH 2
.
O
H
+
N C O
– C 2 H 5
.
+
m/z 56
+
+
CH 2 =N=C=O
+ .
+ .
+ .
– CH O
.
2-Piperidone:
N
H
O
N
H
C
CH 2
.
O +
N
H
O
H 2 C
N
H
O
H
+
N
C
O
H
H
+
C O
+
O
N
H
C
O
N
H
+
+
CH 2 =NH 2
m/z 30
+
m/z 70
m/z 71
m/z 55
m/z 99
m/z 99
m/z 99
– CHO
.
– C 2 H 5
.
– CH 2 NH
– C 2 H 4
+ .
+ .
+ .
.
.
Molecular ion: Often observable; more abundant than for the corresponding
lactones.