FIRST DETERMINATION OF ABSOLUTE CONFORMATION BY RAMAN SPECTROSCOPY

Abstract

The technique and general theory of Raman circular intensity differencial (C.I.D.) is presented. Two different methods of establishing the absolute configuration have been developed. In one method, we calculate the C.I.D. associated with the two normal modes resulting from the coupling of two internal coordinates belonging to two chirally disposed identical groups. It is shown to be dependant of the only electrical polarisiblity tensor $\alpha$, if one neglects the dimensions of groups as compared to the distance between them. In case of $C_{2v}$ groups and $A_{1}$ internal modes, the C.I.D. depends only on one parameter: $\tau = (\alpha_{zz} - \alpha_{xx})/(\alpha_{yy} - \alpha_{zz})$ besides those specifying the geometry. The equations are applied to the coupled $CH_{2}$ scissoring region of four terpenes. $\tau$ is deduced from the Raman spectrum of cyclohexane. Results are in good agreement with reported C.I.D.’s. The other method which will be discussed shortly is based on an integral property of the C.I.D. spectra. The potential applications of these methods to stereochemical problems will be discussed.