A hybrid method for estimation of molecular dynamics of diazepam-density functional theory combined with NMR and FT-IR spectroscopy.

Reorientation of the molecule of diazepam was investigated by calorimetric methods, IR absorption and NMR. The investigation of dynamics was complemented by density functional study (DFT) of vibrational frequencies and infrared intensities, calculations of steric hindrances and Monte Carlo simulations. The results indicated the occurrence of reorientation jumps of the CH(3) group and conformational motion of the benzodiazepine ring. The activation parameters of the methyl group reorientation were determined and the activation barrier obtained was in good agreement with the theoretically estimated value. The FT-IR spectra were assigned using results of DFT calculations.