The structure of Dimedone and the effect of solvents on Keto-enol Tautomerism

Abstract

An infra-red spectroscopic examination of dimedone has shown that in non-polar solvents this compound exists in the diketo- rather than the mono-en01 form. Such behaviour suggests that where intramolecular hydrogen bonding cannot stabilize the enolic form, as it can, for example, in acetyl acetone, there is little tendency for the 1,3-diketones to enolize. In other media, the equilibrium shifts in favour of the mono-enol, thorn solvents which are basic or easily form hydrogen bonds having the greatest influence. On the other hand the dielectric constant per se of the solvent has little effect on the equilibrium. In contrast with diosphenol, it is shown that the hydroxyl group in the mono-enolic form of dimedone has some effect on the mesomerism of the system -C=C-C=O.