Une Serie de N-(2,3-Dihydroxybenzilidene)amines: Manifestation d'Equilibres Tautomeres

Article abstract of DOI:10.1107/S0108270194002945

The crystal structures of five N-(2,3-dihydroxybenzylidene)amine derivatives, C7H6NO2-R are presented and discussed. All the molecules are characterized by the presence of a strong intramolecular hydrogen bond, O-H...N, which determines the formation of a six-membered pseudocycle in the same plane as the phenolic moiety.When R is an aromatic ring, the molecules are either planar or make a dihedral angle which does not exceed 10^o.Except for (2), all the molecules are associated as dimers with two intermolecular O-H...O hydrogen bonds involved in a ten-membered pseudocycle.In compound (5), an intermolecular hydrogen bond wiht a third molecule is also observed.In (2), the cohesion of the crystal is mainly secured by the intermolecular hydrogen bond between the hydroxyl group and the aromatic p-methylphenyl ring.Unlike the N-(2-hydroxybenzylidene)amines for which the phenolic tautomer largely prevails, in the present compounds the quinonic form is present in significant amounts and is even dominant for compound (4).Hence the presence of a second vicinal hydroxyl group determines an important shift in the tautomeric equilibrium.