Correlation of circular dichroism and conformation in γδ- and δε-unsaturated ketones

Abstract

C.d. spectra of a number of unsaturated ketones (several γδ- and one δε-) are discussed. The orientation of the CC bond with respect to the CO group in terms of the pathway via the intervening C–C bonds is important in determining the sign of the Cotton effect of the n→π* transition, not the position of the double bond in a particular octant. Octant contribution can be expected only in those orientations of bonds which permit effective π back-donation from CC via C–C bonds to the carbonyl group. Anomalous solvent effects on steroidal Δ⁶-3-ketones are discussed.