4-Butyl-amino-3-nitro-benzoic acid.

The asymmetric unit of the title compound, C(11)H(14)N(2)O(4), comprises four crystallographically independent mol-ecules (A, B, C and D) with similar geometries. In each mol-ecule, the butyl-amino side chain is in an extended conformation, and the carboxyl and butyl-amino groups are almost coplanar with the attached benzene ring; the nitro group is slightly twisted away from the benzene ring. In the asymmetric unit, the benzene rings of mol-ecules A, B and C are stacked parallel to one another, with a centroid-centroid distance of 3.6197 (11) or 3.6569 (11) Å, indicating π-π inter-actions. An intra-molecular N-H⋯O hydrogen bond is observed in each independent mol-ecule. In addition to the π-π inter-actions, the crystal packing is consolidated by inter-molecular O-H⋯O and C-H⋯O hydrogen bonds and C-H⋯π inter-actions. The crystal studied was a non-merohedral twin. The minor twin component refined to a value of 0.290 (1).