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.