Chiroptical properties of lactones. Part II. Electronic rotatory strengths of the n→π* transition in saturated γ- and δ-lactones

Abstract

The chiroptical properties associated with the n→π* transition of dissymmetric saturated γ- and δ-lactones are calculated and relationships between the chiroptical observables and the stereochemical and electronic structural features of these systems are examined. The calculations are based on the INDOMO model for the electronic structure of the molecular systems and excited states are constructed in the virtual orbital-configuration interaction approximation. The highest and second highest occupied orbitals calculated for each of the 17 structures studied are, respectively, the in-plane n and out-of-plane π* nonbonding orbitals localized on the OC–O group. The lowest lying singlet state is nπ* and the calculated transition wavelengths for transitions to this state lie in the range 197–230 nm. The n→π* rotatory strengths and dissymmetry factors calculated for the various structures are in general agreement with experiment. Furthermore, spectra–structure relationships deduced from the calculated results tend to support the empirical and semi-empirical relationships presently applied to chiral γ- and δ-lactones.