(E)-2-Hydr-oxy-6-[(4-propyl-phenyl)-iminiometh-yl]phenolate.

The title compound, C(16)H(17)NO(2), crystallizes with three crystallographically independent zwitterionic mol-ecules in the asymmetric unit which differ significantly in the orientations of the propyl side chains. The dihedral angles between the two benzene rings in the three mol-ecules are 6.17 (7), 6.75 (7) and 23.67 (7)°, respectively. In each independent mol-ecule, an intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, each independent mol-ecule exists as part of an O-H⋯O hydrogen-bonded centrosymmetric R(2) (2)(10) dimer.