Chiroptical studies. Part 96. Short wavelength (190 nm) circular dichroism of ketones

Abstract

C.d. data in the region of 190 nm are analysed for 152 chiral ketones, by the empirical methods used recently in re-evaluating c.d. data for the n→π* transition (ca. 290 nm). The 190-nm c.d. band for compounds of either trans- or cis-decalone type is generally dominated by octant-consignate contributions of any axial alkyl substituents at the ring junction positions ‘α’ or ‘β’ to the carbonyl function. Group increments (δδIµ) derived from this analysis allow the ‘prediction’ of values of ΔIµ, although less accurately than for the n→π* band. Compounds which include a cyclopentanone ring exhibit c.d. behaviour with signs which depend both upon the contributions of any ‘α’- or ‘β’-axial methyl substituents and on the conformation of the cyclopentanone ring itself. The structural information which can be obtained from the ‘190 nm’ c.d. band differs markedly in some respects from that provided by the well known n→π* c.d. band. Some applications are suggested.