N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
426
8 Mass Spectrometry
In the case of alkyl phthalates (other than dimethyl phthalate), alkenyl elimination
from one ester group to give the protonated ester acid, followed by alkene elimination from the other ester group, and subsequent water elimination to the protonated
anhydride ion, which forms the base peak at m/z 149.
ESI-MS/MS: Elimination of alcohol generates the acyl ion Alk–CO + , which
subsequently loses CO. The cleavage of the Alk–O bond is also an important
reaction. Depending on the proton affinity of the products it leads to the protonated
acid or to the alkyl cation:
[Ar–COOAlk + H] +
[ArCOOH + H] + + [Alk - H]
[Ar–COOAlk + H] +
Alk + + RCOOH
Ion series: Aromatic hydrocarbon fragments, C n H n and C n H n±1 (m/z 39, 51–53,
63–65, 75–77, …).
Intensities: Prominent maximum at the mass of the related benzoyl ion and its
decarbonylation product.
Molecular ion: Usually strong.
Lactones
Fragmentation: The most prominent reaction is the loss of substituents (or H · ) at
the O-bearing C atom, followed by decarbonylation (Δm 28), decarboxylation (Δm
44, mainly in smaller molecules), and ketene elimination (Δm 42). Decarboxylation
of M +· is rarely significant. Competing reactions are several kinds of primary ring
cleavages. Aromatic lactones show maxima due to two consecutive decarbonylations.
Ion series: No specific ion series. The acetyl ion (m/z 43) is often an important
fragment.
Intensities: Maxima at the mass resulting from loss of substituents at the C atom
next to oxygen. Otherwise, intensive peaks evenly distributed over the whole mass
range.
Molecular ion: Usually of low intensity and easily protonated to [M+H] + in aliphatic
lactones; abundant in the case of aromatic lactones.
8.11.6 Amides and Lactams
Amides of Aliphatic Carboxylic Acids
Fragmentation: Alkene elimination on the acid side via McLafferty reaction to
yield the corresponding acetamide radical cation. Loss of alkenes on the amine
side to give the ion of the desalkyl amide, often via double H rearrangement to the
protonated desalkyl amide ion. Bond cleavage on both sides of the carbonyl group.
Cleavage of the C–C bond attached to N, and the β,γ-C–C bond (relative to N):
N
H
R
O
– R
.
N
O
+
– CH 2 C=O
∆m 42
N
H
H
+
m/z 44
H
+ .
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
426
8 Mass Spectrometry
In the case of alkyl phthalates (other than dimethyl phthalate), alkenyl elimination
from one ester group to give the protonated ester acid, followed by alkene elimination from the other ester group, and subsequent water elimination to the protonated
anhydride ion, which forms the base peak at m/z 149.
ESI-MS/MS: Elimination of alcohol generates the acyl ion Alk–CO + , which
subsequently loses CO. The cleavage of the Alk–O bond is also an important
reaction. Depending on the proton affinity of the products it leads to the protonated
acid or to the alkyl cation:
[Ar–COOAlk + H] +
[ArCOOH + H] + + [Alk - H]
[Ar–COOAlk + H] +
Alk + + RCOOH
Ion series: Aromatic hydrocarbon fragments, C n H n and C n H n±1 (m/z 39, 51–53,
63–65, 75–77, …).
Intensities: Prominent maximum at the mass of the related benzoyl ion and its
decarbonylation product.
Molecular ion: Usually strong.
Lactones
Fragmentation: The most prominent reaction is the loss of substituents (or H · ) at
the O-bearing C atom, followed by decarbonylation (Δm 28), decarboxylation (Δm
44, mainly in smaller molecules), and ketene elimination (Δm 42). Decarboxylation
of M +· is rarely significant. Competing reactions are several kinds of primary ring
cleavages. Aromatic lactones show maxima due to two consecutive decarbonylations.
Ion series: No specific ion series. The acetyl ion (m/z 43) is often an important
fragment.
Intensities: Maxima at the mass resulting from loss of substituents at the C atom
next to oxygen. Otherwise, intensive peaks evenly distributed over the whole mass
range.
Molecular ion: Usually of low intensity and easily protonated to [M+H] + in aliphatic
lactones; abundant in the case of aromatic lactones.
8.11.6 Amides and Lactams
Amides of Aliphatic Carboxylic Acids
Fragmentation: Alkene elimination on the acid side via McLafferty reaction to
yield the corresponding acetamide radical cation. Loss of alkenes on the amine
side to give the ion of the desalkyl amide, often via double H rearrangement to the
protonated desalkyl amide ion. Bond cleavage on both sides of the carbonyl group.
Cleavage of the C–C bond attached to N, and the β,γ-C–C bond (relative to N):
N
H
R
O
– R
.
N
O
+
– CH 2 C=O
∆m 42
N
H
H
+
m/z 44
H
+ .