N-(4-Chloro-2-methyl-phen-yl)maleamic acid.

In the mol-ecular structure of the title compound, C(11)H(10)ClNO(3), the conformation of the N-H bond in the amide segment is syn to the ortho-methyl group in the phenyl ring. The C=O and O-H bonds of the acid group are in the relatively rare anti position with respect to each other. This is an obvious consequence of the hydrogen bond donated to the amide carbonyl group. The central oxobutenoic acid core C(=O)-C=C-C-OH is twisted by 31.65 (6)° out of the plane of the 4-chloro-2-methyl-phenyl ring. An intra-molecular O-H⋯O hydrogen bond occurs. In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into infinite chains running along the a axis.