FTIR study of five complex beta-lactam molecules.

Five monocyclic 4-benzoyl-4-phenyl-beta-lactam derivatives in carbon tetrachloride solutions were studied by FTIR spectroscopy. The Fourier self-deconvolution method was applied to enhance the resolution of the FTIR spectra. The calculated spectra of these five compounds, which were obtained by quantum mechanical methods, were compared with FTIR data. A complete assignment of the vibrational frequencies in the 4000-400 cm(-1) range was made. Several vibrations were selected as being useful to characterize the beta-lactam ring. Substituents on N1 (p-methoxyphenyl) and C3 (methyl, phenyl, maleimidyl, and phthalimidyl) on the beta-lactam ring increase the amide resonance and the planarity of the ring. The optimized geometry along with the total electric charges on the four atoms of the ring support an antibiotic action mechanism by a nucleophilic attack of the enzymes on the carbonyl carbon atom of the beta-lactam ring.