3.5 Heteroaromatics
59
Assignment
Range
Comments
≈200–210 nm
In benzene and alkylbenzenes
(log ε ≈4)
≈260 nm (log ε ≈2.4)
3.5 Heteroaromatic Compounds
Assignment
Range
Comments
ar C–X
ar C–C
120–160 ppm
100–150 ppm
H–C ar
6–9 ppm
Coupling constants in 6-membered rings
similar to those in aromatic hydrocarbons;
smaller in 5-membered rings
H–N ar
7–14 ppm
Strongly solvent dependent, generally broad
ar C–H st
3100–3000 cm -1 Often multiple bands, weak
ar N–H st
3500–2800 cm -1
ar C–C st
≈1600 cm -1
≈1500 cm -1
≈1450 cm -1
Often split, sometimes not all bands observable
ar C–H δ oop
1000–650 cm -1 Often strong, frequently multiple bands
Molecular ion
Strong, often base peak
Fragments
m/z 39, 50–53,
63–65, 75–78,
[M-26] +· , [M-39] +
Often doubly charged fragment ions
m/z 45 [CHS] +
S-Heteroaromatics
Benzyl-analogous
cleavage
Rearrangements
Loss of HCN (Δm 27, N-heteroaromatics)
Loss of CO (Δm 28, O-heteroaromatics)
Loss of CS (Δm 44, S-heteroaromatics)
cf. UV/Vis Reference Spectra, Chapter 9.5.3
UV
13 C
1 H
IR
MS
UV