N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
402
8 Mass Spectrometry
Quaternary Ammonium Salts
EI-MS: Decomposition in the ion source produces mixtures of a tertiary amine and
the adduct of an alkyl group with the anion (e.g., an alkyl halide).
ESI-MS/MS: Elimination of an alkyl radical or of an alkane:
[R 1 N(CH 3 ) 3 ] +
[R 1 N(CH 3 ) 2 ] + .
+ CH 3
.
[R 1 N(CH 3 ) 3 ] +
[R 1 N(CH 3 )=CH 2 ] + + CH 4
Cycloalkylamines
Fragmentation: The most important primary reaction is the ring cleavage next to
the N atom, followed by H rearrangement and loss of an alkyl residue. Some elimination of amine, R 1 R 2 NH.
(CH 2 ) n
N H
R
(CH 2 ) n
N
R
H
– C n+ 1 H 2n+ 3
N H
R +
[55 + R]
+
.
+ .
+ .
.
(CH 2 ) n
NH
H
– (CH 2 ) n+ 2
(CH 2 ) n
NH
R
R
NH
+
R
– R
.
NH
+
m /z 56
+ .
+ .
.
.
Ion series: Even-mass fragments of the type C n H 2n N (m/z 42, 56, 70, 84, …).
Intensities: Intensive local maxima evenly distributed over the whole mass range.
Molecular ion: Usually significant.
Cyclic Amines
Fragmentation: Dominating primary reaction is the cleavage of C–C bonds next to
N, resulting in the loss of substituents next to N or in primary ring cleavage. Primary
ring cleavage is followed by H rearrangement and loss of alkenes or alkyl groups.
The most important primary fragmentation for substituted cyclic amines is the loss
of substituents at C atoms next to N.