Redetermination of the β-polymorph of p-amino­benzoic acid

Single crystals of p-amino­benzoic acid, C₇H₇NO₂, were grown from water. In the structure, there is one mol­ecule of the acid present in the asymmetric unit. Hydrogen bonds between adjacent mol­ecules lead to the formation of a three-dimensional network.

4-Amino­phenyl­acetic acid

Crystals of the title compound, C₈H₉NO₂, were obtained from ethyl acetate. The structure consists of the acid in its zwitterionic form. In the crystal structure, each mol­ecule interacts through strong N—H...O hydrogen bonds with six adjacent mol­ecules, yielding a three-dimensional network.

4-Hydroxy­phenyl­acetic acid

The crystal structure of commercially available 4-hydroxy­phenyl­acetic acid, C₈H₈O₃, is non-centrosymmetric, with four hydrogen bonds between each mol­ecule and adjacent mol­ecules. The hydrogen bonds link the mol­ecules in the crystal structure into an infinite three-dimensional framework.