Infrared Study of β-Propiolactone in Various Solvent Systems and other Lactones

Publisher Website
Google Scholar
Abstract
Many lactones exhibit two significant bands in the carbonyl stretching region which result from Fermi resonance interaction between vC = O and a combination or overtone of a lower-lying fundamental (or fundamentals). However, for β-propiolactone, three significant bands in the carbonyl stretching region of the spectrum are observed. These bands result from vC = O in Fermi resonance between the combination tone v6 + v13, A′ and 2 v10, A'. The extent of Fermi resonance interaction between vC = O and the combination and/or overtone is dependent upon the solvent system. Approximate unperturbed vC = O frequencies have been calculated, and these vC = O frequencies decrease in frequency in the solvent order n-hexane, carbon tetrachloride, and chloroform. The unperturbed vC = O frequencies were also calculated with the use of reported frequencies and band intensities for many other lactones, and the unperturbed vC = O frequencies decrease significantly as the amount of ring strain is reduced in the lactone structures. An equation, based on perturbation theory for obtaining approximate unperturbed vC = O frequencies for situations where three modes are in Fermi resonance, was developed and used to assign the unperturbed vC = O frequencies for β-propiolactone in various solvent systems. This method assumes that all or nearly all of the intensity in the three bands in Fermi resonance arises from the vC = O mode.