Conformational free energy differences in steroids. Part II. Equilibration of 3α-methyl-5α- and -5β-cholestan-6-ones, and of 3α-chloro-5α- and -5β-cholestan-6-ones

Abstract

The conformational preference of the methyl group determined by equilibration of 3α-methyl-5α-cholestan-6-one with its 5β-isomer agreed well with values obtained in other systems. For 3α-chlorine the method is invalidated by electrostatic interactions with the 6-keto-group, which are less in the 5α-than in the 5β-isomer. Calculated values of these interactions were in reasonable agreement with the experimental findings. Equilibrium constants were determined by an improved optical rotatory dispersion technique.