Structural analyses of 4-benzoylpyridine thiosemicarbazone using NMR techniques and theoretical calculations

The reaction of 4-benzoylpyridine and thiosemicarbazide gave at least two products, characterized by 1H, 13C and 2D NMR experiments as E- and Z-4-benzoylpyridine thiosemicarbazone. Conformational distribution of E-4-benzoylpyridine thiosemicarbazone was carried out by means of the PM3 method, and geometry optimization using the Density Functional Theory (DFT), with consideration of solvent effects by PCM. The results indicated that the conformation of lowest energy is the same as that obtained in the solid, as confirmed by X-ray crystal structure determinations. A similar procedure used to determine the conformational distribution of Z-4-benzoylpyridine thiosemicarbazone suggested the existence of a dimer formed by intermolecular hydrogen bonds in the gas phase as well as in solution, which is in accordance with NOESY correlations.