N-(4-Chloro-3-nitro-phen-yl)maleamic acid.

In the mol-ecule of the title compound, C(10)H(7)ClN(2)O(5), the acyclic C=C double bond is cis configured. The C=O and O-H bonds of the acid group are in a relatively rare anti position to each other, due to the donation of intramolecular hydrogen bond to the amide by the carboxyl group. The nitro group is significantly twisted [dihedral angle = 66.9 (3)°] out of the plane of the remaining atoms, which are almost coplanar (r.m.s. deviation for non-H atoms except the nitro group = 0.202 Å). In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into zigzag chains running along the b axis.