Gallic acid

Anhydrous 3,4,5-trihydroxybenzoic acid, C7H6O5, is essentially planar, with its non-H atoms exhibiting mean and maximum deviations from coplanarity of 0.014 and 0.0377 (5) angstrom, respectively. The C-C-C-OH torsion angle about the bond linking the carboxyl group to the benzene ring is -0.33 (10)degrees. In the crystal, the -COOH groups form centrosymmetric hydrogen-bonded cyclic dimers [graph set R-2(2)(8)] and the phenolic -OH groups participate in both intra- and intermolecular hydrogen bonds, forming a three-dimensional network structure.