Application of the νD/νH ratio to the assignment of C-H(D) and ring vibrations in the infrared spectra of imidazole and its deuterated analogues

The IR spectra (4000-150 cm^?1)of imidazole and its I-, 2,4,5- and 1,2,4,5-deuterated analogues are discussed. All twenty-one fundamental IR active imidazole vibrations are assigned by employing the ν^D/ν^H ratio which is defined as the ratio between the frequencies of corresponding IR bands in the spectra of a ring-deuterated heterocyclic (or aromatic) molecule and its normal analogue. The results suggest that some previously reported assignments require revision.