The methyl esters of 3β- and 3α-cholestanecarboxylic acids and of 3β- and 3α-cholestene-Δ⁵-carboxylic acids have been prepared and their rates of acid-catalyzed hydrolysis in 90:10 dioxane-water at several temperatures determined. Differences in the absolute and the relative rates of the first two (saturated) esters and those of methyl trans- and cis-5-t-butylcyclohexanecarboxylates are believed due to curvature of the steroid polycyclic structure and to greater rigidity of the A-ring in the steroids than in the monocyclic compounds. Failure of the kinetic method to permit calculations of the conformational free energy of the carbomethoxy group is believed due to the same two factors plus a solvent effect. In case of the last named ester, methyl 3α-cholestene-Δ⁵-carboxylate, hydrolysis under the kinetic conditions resulted in a Y-lactone being formed, thereby precluding quantitative rate determinations. The Y-lactone structure was tentatively confirmed.
