A spectrophotometric study of the tautomeric monoanions of (Z)-5-arylmethylenehydantoins

Abstract

First ionization of (Z)-5-arylmethylenehydantoins in aqueous dimethyl sulphoxide yields a tautomeric mixture of monoanions by deprotonation at N-1 or N-3. By using appropriate 3-methyl and 1-methyl derivatives as models, the equilibrium proportions of the monoanions of the N-unsubstituted compounds have been estimated from the electronic spectra. The percentage of the N-1 anion increases with electron-withdrawing substituents in the benzene ring and with increasing concentration of dimethyl sulphoxide in the solvent mixture.