Conformational free energy differences in steroids. Part I. Equilibration of 3β-substituted 5α- and 5β-cholestan-6-ones

Abstract

Equilibration of 3β-substituted 5α-cholestan-6-ones with their 5β-isomers provided a method for the determination of the conformational free energy difference between an axial and an equatorial 3-substituent. These differences for the hydroxy, acetoxy, methoxy, chloro, and methyl groups agree reasonably well with values obtained in other systems. The conformation of ring A in these compounds is probably very similar to that in the corresponding monocyclic cyclohexane derivatives with axial and equatorial substituents. A new method is therefore available for the determination of conformational free energy differences in cyclohexane systems.