NMR Study of Isolobal N-CH3+, N-BH3 and N-BF3 Imidazole Derivatives

Article abstract of DOI:10.1002/mrc.1260310207

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 ⁺ (122-124 ppm) or ⁺ (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.Key-Words: Imidazole-BH3, Imidazole-BF3, 1H, 11B and 13C NMR, Longe-range J(C,H) values