(E)-2-[(4-Ethoxy­phen­yl)imino­meth­yl]-4-methoxy­phenol

In the mol­ecule of the title compound, C16H17NO3, the aromatic rings are oriented at a dihedral angle of 29.25 (8)°. An intra­molecular O—H⋯N hydrogen bond results in the formation of a nearly planar [maximum deviation 0.034 (13) Å] six-membered ring, which is oriented at dihedral angles of 0.91 (1) and 28.91 (12)° with respect to the aromatic rings. The title mol­ecule is a phenol–imine tautomer, as evidenced by C—O, C—N and C—C bond lengths. In the crystal, mol­ecules are linked by inter­molecular C—H⋯O hydrogen bonds that generate C(8) chains

(Z)-6-[(5-Chloro-2-hydroxy­phenyl)­aminomethyl­ene]-2-ethoxy­cyclo­hexa-2,4-dienone

The title compound, C15H14ClNO3, exists as the keto–amine form in the crystal and two intra­molecular N—H⋯O hydrogen bonds are observed. The aromatic rings are oriented at a dihedral angle of 5.85 (8)°. In the crystal structure, inter­molecular O—H⋯O and C—H⋯O hydrogen bonds link the mol­ecules into chains. A π–π contact between the benzene rings [centroid–centroid distance = 3.6623 (10) Å] further stabilizes the structure

3-Diethyl­amino-6-[(Z)-(4-hy­droxy­anilino)methyl­idene]cyclo­hexa-2,4-dienone

In the mol­ecule of the title compound, C17H20N2O2, the aromatic rings are oriented at a dihedral angle of 6.23 (22)°. Intra­molecular N—H⋯O hydrogen bonding involving the amine H atom and the carbonyl O atom affects the conformation of the mol­ecule. One of the ethyl arms is disordered over two conformations, with occupancies of 0.59 (2) and 0.41 (2). The crystal packing is stabilized by inter­molecular C—H⋯O and O—H⋯O hydrogen bonds, and weak C—H⋯π inter­actions

3-[(E)-(4-Ethyl­phen­yl)imino­meth­yl]benzene-1,2-diol

The title compound, C15H15NO2, adopts the enol–imine tautomeric form. The dihedral angle between the two benzene rings is 48.1 (1)°. Intra­molecular O—H⋯N and O—H⋯O hydrogen bonds generate S(6) and S(5) ring motifs, respectively. In the crystal, mol­ecules are linked into centrosymmetric R 2 2(10) dimers via pairs of O—H⋯O hydrogen bonds and the dimers may interact through very weak by π–π inter­actions [centroid–centroid distance = 4.150 (1) Å]. The ethyl group is disordered over two orientations, with occupancies of 0.587 (11) and 0.413 (11)

(E)-4-Meth­oxy-2-[3-(trifluoro­meth­yl)phenyl­imino­meth­yl]phenol

The title compound, C15H12F3NO2, adopts the phenol–imine tautomeric form, with the H atom attached to oxygen rather than to nitro­gen. There are two independent mol­ecules aligned nearly parallel in the asymmetric unit with their trifloramethyl groups pointing in opposite directions. The dihedral angles between the aromatic rings are 40.43 (1)° in the first mol­ecule and 36.12 (1)° in the second. Strong intra­molecular O—H⋯N hydrogen bonding generates S(6) ring motifs. Weak inter­molecular C—H⋯O hydrogen bonds link the independent mol­ecules separately into sheets normal to [010]. In addition, C—H⋯π inter­actions are also observed. The F atoms of the trifluoro­methyl groups are disordered over two sets of sites with refined site occupancies of 0.59 (2)/0.41 (2) and 0.62 (3)/0.38 (3), respectively

(E)-3-[(4-Butyl­phen­yl)imino­meth­yl]benzene-1,2-diol

The title compound, C17H19NO2, exists as an enol–imine tautomer. The dihedral angle between the two benzene rings is 4.6 (2)°. The mol­ecular structure is stabilized by intramol­ecular O—H⋯O and O—H⋯N hydrogen bonds which generate S(5) and S(6) ring motifs, respectively. In the crystal, mol­ecules are linked into centrosymmetric dimers by pairs of O—H⋯O hydrogen bonds. In addition, C—H⋯π inter­actions involving both benzene rings are observed

(E)-4-Meth­oxy-2-(o-tolyl­imino­meth­yl)phenol

In the mol­ecule of the title compound, C15H15NO2, the aromatic rings are oriented at a dihedral angle of 15.46 (6)°. An intra­molecular O—H⋯N hydrogen bond results in the formation of a nearly planar six-membered ring [maximum deviation of 0.035 (5) Å for the N atom] which is almost coplanar with the adjacent ring, making a dihedral angle of 0.8 (3)°. The title organic mol­ecule is a phenol–imine tautomer, as evidenced by the C—O, C—N and C—C bond lengths. Mol­ecules are linked by inter­molecular C—H⋯O hydrogen bonds that generate a C(5) chain. C—H⋯π and π–π inter­actions exist in the structure. The π–π inter­action occurs between the phenol ring and its symmetry equivalent at (1 − x, 1 − y, −z), with a centroid–centroid distance of 3.727 (7) Å and a plane-to-plane separation of 3.383 (5) Å, resulting in an offset angle of 24.82 (1)°

(E)-2-Acetyl-4-[(3-methyl­phenyl­)diazen­yl]phenol: an X-ray and DFT study

The title compound, C15H14N2O2, an azo dye, displays a trans configuration with respect to the N=N bridge. The dihedral angle between the aromatic rings is 0.18 (14)°. There is a strong intra­molecular O—H⋯O hydrogen bond. Geometrical parameters, determined using X-ray diffraction techniques, are compared with those calculated by density functional theory (DFT), using hybrid exchange–correlation functional, B3LYP and semi-empirical (PM3) methods

1-{5-[(E)-(2-Fluoro­phen­yl)diazen­yl]-2-hy­droxy­phen­yl}ethanone

Theere are two independent mol­ecules in the asymmetric unit of the title compound, C14H11FN2O2, each with a trans configuration with respect to the azo double bond. The dihedral angle between the aromatic rings is 17.21 (2)° in one mol­ecule and 19.06 (2)° in the other. Each of the independent mol­ecules has an intra­molecular O—H⋯O hydrogen bond. In the crystal, mol­ecules are stacked along [100]

(E)-2-Hydr­oxy-6-[(4-propyl­phenyl)­iminiometh­yl]phenolate

The title compound, C16H17NO2, crystallizes with three crystallographically independent zwitterionic mol­ecules 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 mol­ecules are 6.17 (7), 6.75 (7) and 23.67 (7)°, respectively. In each independent mol­ecule, an intra­molecular N—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, each independent mol­ecule exists as part of an O—H⋯O hydrogen-bonded centrosymmetric R 2 2(10) dimer