Nuclear quadrupole coupling in the microwave spectrum of imidazole

The quadrupole hyperfine structure in the rotational spectrum of two isotopic forms of imidazole has been analyzed to obtain principal nuclear quadrupole coupling constants for the two nonequivalent nitrogen atoms. The results have been compared with field gradient tensors calculated using INDO molecular orbital wavefunctions and some implications for the electronic structure of imidazole are mentioned. Comparisons with pyrazole and the NQR results for imidazole are also made.