NMR Study of isolobal N‐CH3+, N‐BH3 and N‐BF3 imidazole derivatives

Some N‐BH3, N‐BF3, N+‐CH3 and N+‐H imidazole derivatives have been prepared and their 13C, 11B and 1H NMR spectra studied. The effect of the different substituents was analysed. The isolobal character of the N‐BH3 and N‐CH3 derivatives is reflected in their spectra. In the 13CH coupled spectra of N‐borane adducts, the hydrides appear to be coupled with the heterocyclic carbon atoms. The C‐4 chemical shift value is indicative of the nature of the N‐substitution: lone pair (128–130 ppm), BH3 (126–128 ppm), BF3 and [CH3]+ (122–124 ppm) or [H]+ (117–119 ppm). The latter values allowed the chemical shifts of frozen imidazole to be estimated: 128 ppm for C‐4 and 117 for C‐5.