Gallic acid
Jianping Zhao, Ikhlas Ahmed Khan, Frank Rolf Fronczek · Acta Crystallographica Section E Structure Reports Online · 2011
Anhydrous 3,4,5-trihy-droxy-benzoic 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 inter-molecular hydrogen bonds, forming a three-dimensional network structure.