N-(4-Methoxyphenyl)maleamic acid

In the title compound, C11H11NO4, the asymmetric unit contains two unique molecules, both of which are almost planar, with r.m.s. deviations of 0.047 and 0.059 Å. The dihedral angles between the benzene ring and the plane of maleamic acid unit are 3.43 (5) and 5.79 (3)° in the two molecules. The molecular structures are stabilized by a short intramolecular O—H⋯O hydrogen bond within each maleamic acid unit. In the crystal, intermolecular N—H⋯O hydrogen bonds link the molecules into zigzag chains extending along [10]. Weak intermolecular C—H⋯O hydrogen bonds also exist.