Conformational study of ketoprofen by combined DFT calculations and Raman spectroscopy.

A conformational study of ketoprofen was carried out by both density functional theory (DFT) calculations and Raman spectroscopy. Nine different geometries were found to correspond to energy minimum conformations but only one of them was experimentally detected in the condensed phase spectra. Those rotations which interconvert the five most stable conformers were studied and the intramolecular interactions governing the corresponding conformational preferences were assessed. A thorough vibrational analysis was performed, leading to the assignment of both the solid and liquid spectra. Evidence for formation of intermolecular hydrogen bonds between carboxylic groups of adjacent ketoprofen molecules, leading to dimeric entities, was obtained.