doi:10.1016/S0022-2860(01)00759-1

1-Benzoylazoles: an experimental (NMR and crystallography) and theoretical study

Five N-benzoylazoles (imidazole, pyrazole, indole, benzimidazole and carbazole) have been prepared following modified literature procedures. Their NMR spectra in solution (¹H, ¹³C and ¹⁵N) have been measured. The crystal structures of 1-benzoylindole and 9-benzoylcarbazole have been determined by X-ray crystallography and the corresponding ¹³C NMR spectra in the solid state have been measured by the CPMAS technique. Whereas 1-benzoylindole presents a standard behaviour, 9-benzoylcarbazole shows an unexpected ¹³C CPMAS spectrum with additional splittings. In order to understand this fact, the ¹H and ¹³C NMR spectra in dimethylether at −143°C (130 K) have been recorded and ab initio calculations (RHF/6-311G**) carried out. The corresponding absolute shieldings (GIAO/ RHF/6-311G**) together with the X-ray structure and the ¹³C chemical shifts at low temperature have been used to discuss the CPMAS spectrum. We propose that the supplementary splittings of this spectrum are due to its conglomerate structure.