Gallic acid

Anhydrous 3,4,5-trihy­droxy­benzoic acid, C(7)H(6)O(5), is essentially planar, with its non-H atoms exhibiting mean and maximum deviations from coplanarity of 0.014 and 0.0377 (5) Å, respectively. The C—C—C—OH torsion angle about the bond linking the carboxyl group to the benzene ring is −0.33 (10)°. 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.