N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
408
8 Mass Spectrometry
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, …). Alkene radical cations (C n H 2n , m/z 42, 56, 70, …)
together with isobaric ions of the composition C n H 2n NCO.
Intensities: Intensive peaks mainly in the lower mass range.
Molecular ion: Usually weak or absent. [M-H] + is often more intensive.
Aromatic Cyanates (R–OCN) [8]
Fragmentation: Loss of OCN · (Δm 42) or, to a lesser extent, of CO (Δm 28), with
subsequent HCN elimination (Δm 27).
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 in the higher mass range.
Molecular ion: Strong.
Aliphatic Isocyanates (R–NCO) [8]
Fragmentation: Spectra often very similar to those of the corresponding cyanates.
Cleavage of the C–C bond next to N, the charge remaining on the CH 2 NCO (m/z
56) for short-chain isocyanates and preferably on the alkyl substituent for compounds with a C n > 2 chain (m/z 29, 43, 57, …). Cleavage of the C–N bond with H
rearrangement to give HNCO +· (m/z 43) or alkene +· (m/z 42, 56, 70, …) ions. For
isocyanates with C n > 5 alkyl chains, alkene elimination, yielding m/z 99.
N
O
R
H
+
– R-CH =CH 2
N
O H
m/z 99
R–CH 2 –N=C=O
+
CH 2 –N =C=O
m /z 56
H–N =C=O
m/z 43
R=CH 2
– R=CH 2
– R
.
– CH 2 N CO
.
– HN CO
R
+
+ .
+ .
+ .
+ .
.
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, …). Alkene radical cations (C n H 2n , m/z 42, 56, 70, …)
together with isobaric ions of the composition C n H 2n OCN.
Intensities: Intensive peaks mainly in the lower mass range.
Molecular ion: Usually weak or absent. [M-H] + is often more intensive.
Aromatic Isocyanates (R–NCO) [8]
Fragmentation: Consecutive elimination of CO (Δm 28) and HCN (Δm 27). In
contrast to aromatic cyanates, practically no elimination of NCO · (Δm 42).
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, …).
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
408
8 Mass Spectrometry
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, …). Alkene radical cations (C n H 2n , m/z 42, 56, 70, …)
together with isobaric ions of the composition C n H 2n NCO.
Intensities: Intensive peaks mainly in the lower mass range.
Molecular ion: Usually weak or absent. [M-H] + is often more intensive.
Aromatic Cyanates (R–OCN) [8]
Fragmentation: Loss of OCN · (Δm 42) or, to a lesser extent, of CO (Δm 28), with
subsequent HCN elimination (Δm 27).
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 in the higher mass range.
Molecular ion: Strong.
Aliphatic Isocyanates (R–NCO) [8]
Fragmentation: Spectra often very similar to those of the corresponding cyanates.
Cleavage of the C–C bond next to N, the charge remaining on the CH 2 NCO (m/z
56) for short-chain isocyanates and preferably on the alkyl substituent for compounds with a C n > 2 chain (m/z 29, 43, 57, …). Cleavage of the C–N bond with H
rearrangement to give HNCO +· (m/z 43) or alkene +· (m/z 42, 56, 70, …) ions. For
isocyanates with C n > 5 alkyl chains, alkene elimination, yielding m/z 99.
N
O
R
H
+
– R-CH =CH 2
N
O H
m/z 99
R–CH 2 –N=C=O
+
CH 2 –N =C=O
m /z 56
H–N =C=O
m/z 43
R=CH 2
– R=CH 2
– R
.
– CH 2 N CO
.
– HN CO
R
+
+ .
+ .
+ .
+ .
.
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, …). Alkene radical cations (C n H 2n , m/z 42, 56, 70, …)
together with isobaric ions of the composition C n H 2n OCN.
Intensities: Intensive peaks mainly in the lower mass range.
Molecular ion: Usually weak or absent. [M-H] + is often more intensive.
Aromatic Isocyanates (R–NCO) [8]
Fragmentation: Consecutive elimination of CO (Δm 28) and HCN (Δm 27). In
contrast to aromatic cyanates, practically no elimination of NCO · (Δm 42).
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, …).