AB-INITIO STUDY OF THE BETA-LACTAM RING IN 2-AZETIDINONE AND 3-METHYL-2-AZETIDINONE - CHARACTERIZATION OF THE RING FUNDAMENTAL VIBRATIONS

The beta-lactam molecules of 2-azetidinone and 3-methyl-2-azetidinone were studied by ab initio methods. The calculated spectra of both mole cules were compared with experimental vibrational frequencies of cyclo butane, 2-azetidinone, and 3-methyl-4-benzoyl-4-phenyl-2-azetidinone. The vibrational frequencies and intensities of the normal modes, espec ially from the four-membered ring, were identified. Several frequencie s were proposed as analytically useful to characterize the beta-lactam ring. The relative utility of these ring frequencies was discussed. T he optimized parameters, bond lengths and bond and torsional angles of all molecular structures, were computed. Also calculated were the tot al atomic charges, electronic density, and several thermochemical para meters: ZPE, thermal energy, rotational constants, and entropies.