4-(But-3-enylamino)-3-nitro-benzoic acid.

The asymmetric unit of the title compound, C(11)H(12)N(2)O(4), contains 12 crystallographically independent mol-ecules, labelled A to L. The nitro and carboxyl groups are twisted slightly out of the plane of the attached benzene ring in all independent mol-ecules except mol-ecules G and D. The nitro group is coplanar with the benzene ring in mol-ecule G and the carboxyl group is coplanar with the benzene ring in mol-ecule D. The orientation of the butyl group with respect to the rest of the mol-ecule is different in some of the independent mol-ecules, with the C-C-C-C torsion angles varying from 104.2 (5) to 126.6 (7)°. In each independent mol-ecule, an intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal structure, the 12 independent mol-ecules exist as six pairs of O-H⋯O hydrogen-bonded R(2) (2)(8) dimers. In addition, C-H⋯O hydrogen bonds are observed.