(E)-2-[(3-Fluoro-phen-yl)imino-meth-yl]-4-(trifluoro-meth-oxy)phenol.

The title compound, C(14)H(9)F(4)NO(2), is a Schiff base which adopts the phenol-imine tautomeric form in the solid state. The H atom is located on the hydr-oxy O atom rather than on the N atom. This H atom is involved in a strong intra-molecular O-H⋯N hydrogen bond. The mol-ecule is almost planar, the angle between the benzene rings being 2.14 (13)°.

1-[(E)-(2-Methyl-3-nitro-phen-yl)imino-meth-yl]-2-naphthol.

The title Schiff base compound, C(18)H(14)N(2)O(3), has an inter-mediate state between NH and OH tautomers. The mol-ecular structure is stabilized by an O-H⋯N hydrogen bond. The dihedral angle between the naphthalene ring system and the benzene ring is 37.44 (5)°.

(E)-2-[(4-Chloro-phen-yl)imino-meth-yl]-4-(trifluoro-meth-oxy)phenol.

The title compound, C(14)H(9)ClF(3)NO(2), crystallizes in a phenol-imine tautomeric form, with a strong intra-molecular O-H⋯N hydrogen bond. The dihedral angle between the two benzene rings is 47.62 (9)°. In the crystal, mol-ecules are linked into chains along the c axis by C-H⋯O hydrogen bonds, and weak C-H⋯π inter-actions involving both benzene rings are also observed.

2-[(2,4-Dimethyl-phen-yl)imino-meth-yl]-3,5-dimethoxy-phenol.

X-ray analysis reveals that the title Schiff base compound, C(17)H(19)NO(3), possesses both OH and NH tautomeric character in its mol-ecular structure. The occupancies of the enol and keto tautomers are 0.62 (3) and 0.38 (3), respectively. The presence of the minor keto form could not be confirmed from the IR spectrum. The mol-ecule is approximately planar, the dihedral angle between the planes of the two aromatic rings being 6.97 (8)°. The mol-ecular structure of the major component is stabilized by an intra-molecular O-H⋯N hydrogen bond, which generates an S(6) ring motif (N-H⋯O hydrogen bond in the minor component).

2-[(E)-(2-Morpholinoeth-yl)iminiometh-yl]-4-nitro-1-oxocyclo-hexa-dienide.

The mol-ecule of the title compound, C(13)H(17)N(3)O(4), exists as a zwitterion, with the H atom of the phenol group being transferred to the imine N atom. The C=O, C(Ar)-C(Ar) and C-N bond lengths are in agreement with the oxocyclo-hexa-dienide-iminium zwitterionic form. A strong intra-molecular N(+)-H⋯O hydrogen bond generates an S(6) ring motif. The morpholine ring adopts a chair conformation. In the crystal, mol-ecules are linked into centrosymmetric dimers by inter-molecular N-H⋯O hydrogen bonds. In addition, C-H⋯O hydrogen bonds and very weak C-H⋯π inter-actions are observed.