2-[(2,4-Dimethylphenyl)iminomethyl]-6-methylphenol

The title compound, C16H17NO, is a Schiff base which adopts the phenol–imine tautomeric form in the solid state. The molecule is almost planar, with a dihedral angle of 4.61 (4)° between the aromatic rings. The molecular structure is stabilized by an intramolecular O—H⋯N hydrogen bond which generates a six membered ring.

The title compound, C 16 H 17 NO, is a Schiff base which adopts the phenol-imine tautomeric form in the solid state. The molecule is almost planar, with a dihedral angle of 4.61 (4) between the aromatic rings. The molecular structure is stabilized by an intramolecular O-HÁ Á ÁN hydrogen bond which generates a six membered ring.
They also have a wide ranage of industrial uses such as dyes and pigments (Taggi et al., 2002). Schiff bases have also been employed as ligands for the complexation of metal ions (Aydoğan et al., 2001). Two characteristic properties of Schiff bases, are photochromism and thermochromism (Cohen et al., 1964). In general, Schiff bases display two possible tautomeric forms, the phenol-imine (OH) and the keto-amine (NH) forms. Depending on the tautomers, two types of intramolecular hydrogen bonds are observed: O-H···N in the phenol-imines and N-H···O in keto-amine tautomers.
In the title compound (I, Fig. 1), the molecule is almost planar with a dihedral angle between the aromatic rings [C1/C6 and C9/C14] of 4.61 (4)°. The imino group is coplanar with the hydroxyphenyl ring as it is shown by the C2-C1-C8-N1 torsion angle of -0.9 (2)°. The O-H and C=N bond lengths confirm that (I) exhibits the enol-imine tautomer. The length of the C8=N1 double bond is 1.272 (2) Å which is slightly shorter than the standard value of 1.28 Å but it is consistent with the related sturucture (Köysal et al., 2007). It is also known that Schiff bases may exhibit thermochromism depending on the planarity or non-planarity of the molecule, respectively (Moustakali-Mavridis et al., 1978). Therefore, the title compound may exhibit thermochromic properties.
The phenol H atom forms a strong intramolecular O1-H1···N1 hydrogen bond with the imine N atom. (Table 1, Fig. 1) which generates a six-membered ring, producing a S(6) ring motif (Bernstein et al., 1995), stabilizing the planarity of the molecular skeleton. A packing diagram for (I) with hydrogen bonding geometry is shown in figure 2.

Refinement
C-bound H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.96 Å and U iso (H) = 1.2-1.5U eq (C). The C16-methyl group was refined as idealized disordered one with two positions rotated from each other by 60°. The position of the H1 atom was obtained from a difference map of the electron density in the unit-cell and was refined freely.