N
X
C
Hal
O
N
S
P Si
Natural
Products
Solvents
C
C
C
C C
C
8.9 Nitrogen Compounds
409
Intensities: Intensive peaks in the higher mass range.
Molecular ion: Dominating; base peak for phenyl isocyanate.
Aliphatic Thiocyanates (R–SCN) [8]
Fragmentation: Elimination of HCN (Δm 27) followed by loss of an alkyl group.
The cleavage of the C–C bond next to SCN is unimportant except in short-chain
thiocyanates.
Ion series: Saturated and unsaturated alkyl cations (C n H 2n+1 , m/z 29, 43, 57, … and
C n H 2n-1 , m/z 27, 41, 55, …).
Intensities: Intensive peaks in the lower mass range.
Molecular ion: Weak. Decreasing with increasing chain length and degree of
branching; absent from the spectrum of hexyl thiocyanate. Both [M+H] + and
[M-H] + are detectable. Characteristic 34 S isotope peak at [M+2] +· and [frag+2] for
S-containing fragments (4.5% per S atom).
Aromatic Thiocyanates (R–SCN) [8]
Fragmentation: The most important fragmentation is the elimination of SCN · (Δm
58). Further elimination reactions are loss of CN · (Δm 26), HCN (Δm 27),and CS
(Δm 44).
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, …). Weak signal at m/z 45 (CHS + ) indicates sulfur.
Intensities: Intensive peaks in the higher mass range.
Molecular ion: Dominant; base peak in phenyl thiocyanate. Characteristic 34 S
isotope peak at [M+2] +· and [frag+2] for S-containing fragments (4.5% per S atom).
Aliphatic Isothiocyanates (R–NCS) [8]
Fragmentation: Cleavage of the C–C bond next to NCS, leading to m/z 72
(CH 2 NCS) or to its homologues if the α-C atom is substituted. Loss of the alkyl
residue with concomitant double hydrogen rearrangement to yield H 2 NCS + (m/z
60). With a C n > 4 alkyl chain, loss of SH · (Δm 33). With C n > 5 alkyl chains, loss
of alkene leading to m/z 115, probably according to the mechanism shown for
aliphatic isocyanates.
Ion series: Mainly saturated and unsaturated alkyl cations (C n H 2n+1 , m/z 29, 43,
57, … and C n H 2n-1 , m/z 27, 41, 55, …). Signal for CH 2 NCS + (m/z 72) or its
homologues (m/z 86, 100, 114, …) if the α-C atom is substituted.
Intensities: Intensive peaks mainly in the lower mass range.
Molecular ion: Medium to weak, decreasing with increasing chain length and
degree of branching. More intensive than in the corresponding thiocyanates; 1%
for hexadecyl isothiocyanate. Both [M+H] + and [M-H] + are relevant. Characteristic
34 S isotope peak at [M+2] +· and [frag+2] for S-containing fragments (4.5% per S
atom).
X
C
Hal
O
N
S
P Si
Natural
Products
Solvents
C
C
C
C C
C
8.9 Nitrogen Compounds
409
Intensities: Intensive peaks in the higher mass range.
Molecular ion: Dominating; base peak for phenyl isocyanate.
Aliphatic Thiocyanates (R–SCN) [8]
Fragmentation: Elimination of HCN (Δm 27) followed by loss of an alkyl group.
The cleavage of the C–C bond next to SCN is unimportant except in short-chain
thiocyanates.
Ion series: Saturated and unsaturated alkyl cations (C n H 2n+1 , m/z 29, 43, 57, … and
C n H 2n-1 , m/z 27, 41, 55, …).
Intensities: Intensive peaks in the lower mass range.
Molecular ion: Weak. Decreasing with increasing chain length and degree of
branching; absent from the spectrum of hexyl thiocyanate. Both [M+H] + and
[M-H] + are detectable. Characteristic 34 S isotope peak at [M+2] +· and [frag+2] for
S-containing fragments (4.5% per S atom).
Aromatic Thiocyanates (R–SCN) [8]
Fragmentation: The most important fragmentation is the elimination of SCN · (Δm
58). Further elimination reactions are loss of CN · (Δm 26), HCN (Δm 27),and CS
(Δm 44).
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, …). Weak signal at m/z 45 (CHS + ) indicates sulfur.
Intensities: Intensive peaks in the higher mass range.
Molecular ion: Dominant; base peak in phenyl thiocyanate. Characteristic 34 S
isotope peak at [M+2] +· and [frag+2] for S-containing fragments (4.5% per S atom).
Aliphatic Isothiocyanates (R–NCS) [8]
Fragmentation: Cleavage of the C–C bond next to NCS, leading to m/z 72
(CH 2 NCS) or to its homologues if the α-C atom is substituted. Loss of the alkyl
residue with concomitant double hydrogen rearrangement to yield H 2 NCS + (m/z
60). With a C n > 4 alkyl chain, loss of SH · (Δm 33). With C n > 5 alkyl chains, loss
of alkene leading to m/z 115, probably according to the mechanism shown for
aliphatic isocyanates.
Ion series: Mainly saturated and unsaturated alkyl cations (C n H 2n+1 , m/z 29, 43,
57, … and C n H 2n-1 , m/z 27, 41, 55, …). Signal for CH 2 NCS + (m/z 72) or its
homologues (m/z 86, 100, 114, …) if the α-C atom is substituted.
Intensities: Intensive peaks mainly in the lower mass range.
Molecular ion: Medium to weak, decreasing with increasing chain length and
degree of branching. More intensive than in the corresponding thiocyanates; 1%
for hexadecyl isothiocyanate. Both [M+H] + and [M-H] + are relevant. Characteristic
34 S isotope peak at [M+2] +· and [frag+2] for S-containing fragments (4.5% per S
atom).