Vibrational Spectra of β-Lactams. I. 2-Azetidinone and Its Isotopic Compounds

Abstract The infrared and Raman spectra of 2-azetidinone and its 1-d, 3,3-d2, and 1,3,3-d3 and their 15N compounds have been recorded, and the observed bands have been assigned on the basis of the isotope effects and the normal coordinate analysis. The refined force constants have reproduced the observed frequencies satisfactorily. The C–N stretching mode is strongly coupled with the N–H bending vibration to give a band near 1380 cm−1. However, this coupling does not give rise to any bands corresponding to the amide II and III bands. The concentration dependence of the infrared spectrum suggests the presence of an equilibrium of monomer \leftrightharpoons cyclic dimer in carbon tetrachloride solution. The solvent effects on the N–H and C=O stretching bands have also been examined.