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 (H-1, C-13 and N-15) 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 C-13 NMR spectra in dimethylether at -143degreesC (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 C-13 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. (C) 2002 Elsevier Science B.V. All rights reserved.