2-[(E)-(2,4-Dimethylphenyl)iminomethyl]phenol

The asymmetric unit of the title compound, C15H15NO, contains two independent molecules, both of which exist in trans configurations with respect to the C=N bonds [1.278 (2) and 1.279 (2) Å]. In each molecule, intramolecular O—H⋯N hydrogen bonds generate S(6) ring motifs. In one molecule, the benzene rings form a dihedral angle of 13.38 (9)°, while in the other molecule the dihedral angle is 30.60 (10)°. In the crystal, the two independent molecules are linked via weak intermolecular C—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, C 15 H 15 NO, contains two independent molecules, both of which exist in trans configurations with respect to the C N bonds [1.278 (2) and 1.279 (2) Å ]. In each molecule, intramolecular O-HÁ Á ÁN hydrogen bonds generate S(6) ring motifs. In one molecule, the benzene rings form a dihedral angle of 13.38 (9) , while in the other molecule the dihedral angle is 30.60 (10) . In the crystal, the two independent molecules are linked via weak intermolecular C-HÁ Á ÁO hydrogen bonds.

Comment
During the last 50 years, a vast number of structural studies on Schiff bases derived from hydroxyaryl aldehydes have been studied. Schiff bases can be synthesized from an aromatic amine and a carbonyl compound in a nucleophilic addition to a hemiaminal followed by elimination of water to the imine (Gallant et al., 2004). These Schiff bases have shown varied redox and electrical behaviors, depending on the involvement of active coordination sites (Kulkarni, 1975;Zhao et al., 1988;Ma & Zhao, 1988). Among the organic reagents actually used, Schiff bases possess excellent characteristics, structural similarities with natural biological substances, relatively simple preparation procedures and the synthetic flexibility that enables the design of suitable structural properties.
In the crystal structure, Fig. 2, molecules A are linked to molecules B via weak intermolecular C5A-H5AA···O1B i hydrogen bonds (Table 1) into pairs.

Experimental
A mixture of salicylaldehyde (0.01 mol) and 2,4 dimethyl aniline (0.01 mol) in presence of glacial acetic acid (0.5 mL) in ethanol (25 mL) was refluxed gently for 4-5 h. The reaction was monitored by TLC. After completion of the reaction, the reaction mixture was poured into a beaker containing crushed ice. The precipitate thus obtained was filtered, dried and recrystallized from ethanol. Yield: 80%, m.p. 425-428 K.

Refinement
H1OA and H1OB atoms were located in a difference Fourier map and refined freely [O1A-H1OA = 0.88 (3) Å, O1B-H1OB = 0.89 (2) Å]. The remaining H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 or 0.96 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. The highest residual electron density peak is located at 0.72 Å from C7A and the deepest hole is located at 1.28 Å from C12B. In the absence of significant anomalous dispersion, 3161 Friedel pairs were merged for the final refinement. Fig. 1. The molecular structure of the title compound showing 30% probability displacement ellipsoids for non-H atoms. Intramolecular hydrogen bonds are shown as dashed lines.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.