NMR Study of isolobal N ‐CH 3 + , N ‐BH 3 and N ‐BF 3 imidazole derivatives

Some N ‐BH 3 , N ‐BF 3 , N + ‐CH 3 and N + ‐H imidazole derivatives have been prepared and their 13 C, 11 B and 1 H NMR spectra studied. The effect of the different substituents was analysed. The isolobal character of the N ‐BH 3 and N ‐CH 3 derivatives is reflected in their spectra. In the 13 CH 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), BH 3 (126–128 ppm), BF 3 and [CH 3 ] + (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.