N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
404
8 Mass Spectrometry
Aromatic Amines
Fragmentation: Dominating cleavage of alkyl bond at N-bearing C atom
(“N-cleavage”) followed by alkene elimination if aliphatic substituents with C n ≥ 2
are present. Otherwise, loss of H · from primary and secondary anilines and benzylic
amines. Loss of HCN from M +· or from fragments. A local maximum at m/z 42 is
typical of an aromatically bonded dimethylamino group.
ESI-MS/MS: Elimination of HCN from [M+H] + . Loss of methyl radical by
homolytic cleavage of the C–N bond in methyl amines:
[ArNHCH 3 + H] +
Ar-NH 2
+ .
+ CH 3
.
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: Dominating maxima by “N-cleavage” and following alkene loss if
aliphatic substituents with C n > 1 are present.
Molecular ion: Abundant if no aliphatic substituents with more than one C atom
are present, otherwise, medium or weak. No tendency to protonate. In primary and
secondary aromatic and benzylic amines, [M-H] + is important.
8.9.2 Nitro Compounds
Aliphatic Nitro Compounds
Fragmentation: Loss of NO · (Δm 30), NO 2
· (Δm 46), and HNO 2 (Δm 47) as well
as the formation of some m/z 30 as N indicator. Spectra with only few characteristic
features.
Ion series: Mixed alkyl and alkenyl fragments, C n H 2n+1 (m/z 43, 57, 71, …) and
C n H 2n-1 (m/z 41, 55, 69, …).
Intensities: Dominant peaks in the lower mass range.
Molecular ion: Weak or missing.
Aromatic Nitro Compounds
Fragmentation: Loss of O (Δm 16), NO · (Δm 30, followed by elimination of CO,
Δm 28), and NO 2
· (Δm 46) from M +· or from a major primary cleavage product.
Extensive rearrangement of the functional group to a nitroso ester.
ESI-MS/MS: The elimination of the radicals NO
.
(Δm 30) and NO 2
.
(Δm 46) is
dominant in ESI-MS/MS spectra. The elimination of HNO (Δm 31) und HNO 2
(Δm 47) from [M+H] + is less abundant.
Ion series: Aromatic fragments corresponding to C n H n and C n H n±1 (m/z 39, 51–53,
63–65, 75–77, …).
Intensities: Intensive peaks mainly in the upper mass range.
Molecular ion: Strong.
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
404
8 Mass Spectrometry
Aromatic Amines
Fragmentation: Dominating cleavage of alkyl bond at N-bearing C atom
(“N-cleavage”) followed by alkene elimination if aliphatic substituents with C n ≥ 2
are present. Otherwise, loss of H · from primary and secondary anilines and benzylic
amines. Loss of HCN from M +· or from fragments. A local maximum at m/z 42 is
typical of an aromatically bonded dimethylamino group.
ESI-MS/MS: Elimination of HCN from [M+H] + . Loss of methyl radical by
homolytic cleavage of the C–N bond in methyl amines:
[ArNHCH 3 + H] +
Ar-NH 2
+ .
+ CH 3
.
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: Dominating maxima by “N-cleavage” and following alkene loss if
aliphatic substituents with C n > 1 are present.
Molecular ion: Abundant if no aliphatic substituents with more than one C atom
are present, otherwise, medium or weak. No tendency to protonate. In primary and
secondary aromatic and benzylic amines, [M-H] + is important.
8.9.2 Nitro Compounds
Aliphatic Nitro Compounds
Fragmentation: Loss of NO · (Δm 30), NO 2
· (Δm 46), and HNO 2 (Δm 47) as well
as the formation of some m/z 30 as N indicator. Spectra with only few characteristic
features.
Ion series: Mixed alkyl and alkenyl fragments, C n H 2n+1 (m/z 43, 57, 71, …) and
C n H 2n-1 (m/z 41, 55, 69, …).
Intensities: Dominant peaks in the lower mass range.
Molecular ion: Weak or missing.
Aromatic Nitro Compounds
Fragmentation: Loss of O (Δm 16), NO · (Δm 30, followed by elimination of CO,
Δm 28), and NO 2
· (Δm 46) from M +· or from a major primary cleavage product.
Extensive rearrangement of the functional group to a nitroso ester.
ESI-MS/MS: The elimination of the radicals NO
.
(Δm 30) and NO 2
.
(Δm 46) is
dominant in ESI-MS/MS spectra. The elimination of HNO (Δm 31) und HNO 2
(Δm 47) from [M+H] + is less abundant.
Ion series: Aromatic fragments corresponding to C n H n and C n H n±1 (m/z 39, 51–53,
63–65, 75–77, …).
Intensities: Intensive peaks mainly in the upper mass range.
Molecular ion: Strong.