2-All-yloxy-5-nitro-benzoic acid.

The mol-ecule of the title compound, C(10)H(9)NO(5), is approximately planar, with the mean planes of the nitro, carboxyl and all-yloxy groups rotated by 8.1 (3), 7.9 (3) and 4.52 (18)°, respectively, from the plane of the benzene ring. Bond lengths in the aromatic ring are influenced by both electronic effects and strain induced by ortho-substitution. In the crystal structure, centrosymmetrically related mol-ecules are paired into dimers through strong O-H⋯O hydrogen bonds.