The chemistry of santonene. Part I. Keto–enol tautomerism in santonene and dihydrosantonene

Abstract

In the solid state, santonene exists in the keto-form, whereas dihydrosantonene exists as the enol. Physical measurements on santonene favour the structure containing 5,6- and 7,11-double bonds, rather than that of the 4,5: 6,7-unsaturated isomer suggested by Nishikawa et al. In solution, a tautomeric equilibrium is set up between keto and enol forms in both compounds. The position of equilibrium was determined for chloroform, methanol, and pyridine solutions, by means of n.m.r. spectra and specific rotations.