N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
388
8 Mass Spectrometry
Indoles
Fragmentation: Analogous to pyrrole; HCN elimination (Δm 27) from M +· and
from fragments. From M +· also CH 2 N · (Δm 28) elimination (in one or two steps).
In methyl-substituted indoles, [M-1] + is dominant. In N-methylindoles, [M-15] + is
significant. Benzylic-type cleavage in C- and N-alkylindoles with or without (nonspecific) H rearrangements.
Ion series: Aromatic ion series.
Intensities: Dominant maxima in the higher mass range.
Molecular ion: Strong. Odd mass for odd number of N atoms in the molecule. No
tendency to protonate. In methyl-substituted indoles, strong signal for [M-1] + .
Quinolines and Isoquinolines
Fragmentation: Similar to pyridine: HCN elimination (Δm 27) from M +· , [M-1] + , and
fragments. In methylquinolines and methylisoquinolines also CH 3 CN elimination
(Δm 41). In alkyl-substituted (C n > 1 ) quinolines, benzylic cleavage dominates
except when neighboring effects of N play a role. For 2- and 8-alkylquinolines as
well as 1- and 3-alkylisoquinolines, see rearrangements in pyridines.
Rearrangements in 8-alkylquinolines:
– R
.
N
R
+
N
– R
.
N
R
+
N
– CH 2 =CHR
N
+
N
CH 2 H
H
H
R
m/z 156
m/z 170
m/z 143
+ .
+ .
+ .
.
Ion series: Aromatic hydrocarbon fragments, C n H n , C n H n±1 , and C n H n±1 N (m/z
39–41, 51–54, 63–67, 75–80, …).
Intensities: Dominant peak for M +· or, if possible, for products of benzylic-type
cleavage.
Molecular ion: Strong, except when benzylic-type cleavage is possible. Odd mass
for odd number of N atoms in the molecule. No tendency to protonate. [M-1] + is
usually present and is strong in alkyl-substituted quinolines.