Experimental and DFT study of pyrazinamide

All the experimental vibrational bands have been discussed and assigned to normal modes or to combinations and overtones on the basis of B3LYP and BLYP calculations. With respect to the study of Kalkar et al. and Wang et al. [Spectrochim. Acta, 45A (1989) 641; Spectrochim. Acta, 56A (2000) 2637.], some modes have been reassigned in the light of present theoretical results. It is also shown that a very good quantitative agreement between the experimental and calculated chemical shifts both for 1H and 13C nuclei can only be reached by modelling the intermolecular interactions. Moreover, theoretical and experimental NMR data suggest that only one of the two protons of NH2 group is involved in intermolecular hydrogen bonds.