The circular dichroism of the n→π* band of cyclic thionocarbonates. Part I. The relationship between the magnitude and sign of the cotton effect, and the chirality of the five-membered thionocarbonate ring

Abstract

A study of model compounds of fixed conformations has shown a relationship between the chirality of a cyclic thionocarbonate and the sign of the Cotton effect associated with its n→π* transition. The signs of the Cotton effects of compounds which are not conformationally restricted may be rationalised in terms of the expected conformational preference of their substituent groups; several examples drawn from the carbohydrates are reported. The magnitude of the Cotton effect of the thionocarbonate of (+)-cyclo-octane-trans-1,2-diol shows the five-membered ring to exist predominantly in one conformation, which is compatible with crown or boat–chair forms of the cyclo-octane ring.