Katsuhiko Ichikawa

Chemical effects of steric strains—XIV: The effect of ring size on the rate of reaction of the cyclanones with sodium borohydride

Abstract The rates of reaction of sodium borohydride with a number of cyclanones(4, 5-, 6-, 7-, 8-, 9-, 10-, 11-, 12-, 13-, 15-, and 17-ring members) were determined at several temperatures in order to ascertain the effect of ring size on the reactivity of the carbonyl group. Cyclobutanone is the most reactive of the ketones examined, followed closely by cyclohexanone. Cyclopentanone is considerably less reactive, followed a sharp drop in reactivity in the 7-, 8-, 9-, and 10-ring derivatives. The rate reaches a minimum in the 10-ring and then increases with the larger rings to the value exhibited by the open-chain derivative, di-n-hexylketone. The trends in reactivity are very similar to those observed in the equilibrium constants for cyanohydrin formation and in other reactions of ring derivatives. The results agree with the predicted effects of ring size on the magnitude of the internal strains (I-strain).