N-[4-(Dimethylamino)benzylidene]-4-methylaniline

The molecules of the title compound, C16H18N2, exists in a trans conformation with respect to the C=N bond [1.270 (3) Å]. The least-squares plane of the dimethylamino group makes a dihedral angle of 1.3 (2)° with the ring to which it is attached. The dihedral angle between the two aromatic rings is 11.70 (2)°. The crystal structure features weak C—H⋯π interactions.

The molecules of the title compound, C 16 H 18 N 2 , exists in a trans conformation with respect to the C N bond [1.270 (3) Å ]. The least-squares plane of the dimethylamino group makes a dihedral angle of 1.3 (2) with the ring to which it is attached. The dihedral angle between the two aromatic rings is 11.70 (2) . The crystal structure features weak C-HÁ Á Á interactions.   Table 1 Hydrogen-bond geometry (Å , ).   (Shah et al., 1992). In addition to that, they show Non-linear optical properties (Ünver et al., 2004). Therefore, successful application of Schiff bases requires a careful study of their characteristics. The least square plane of the dimethylamine group has a dihedral angle of 1.31 (2) ° with the phenyl ring (C9-C14), which shows that they are almost coplanar to each other. The dimethylamine group attached phenyl ring (C9-C14) forms a dihedral angle of 11.70 (2) Å with the methyl group attached phenyl ring (C2-C7).

Experimental
The title compound was synthesized by the reaction of p-dimethylaminobenzaldehyde (10 mmol, 1.14919 g) with ptoluidine (10 mmol, 1.0717 g) in ethanol (25 ml) under reflux condition for six hours. After filtering, drying the solid product was recrystallized from ethanol/THF (5:1 v/v). After five days yellow colour crystals were obtained Which were suitable for X-ray diffraction studies.

Refinement
The positions of hydrogen atoms were localized from the difference electron density maps and their distances were geometrically constrained. The H atoms bound to the C atoms were treated as riding atoms, with d(C-H) = 0.93 Å and U iso (H) = 1.2U eq (C) for aryl atoms; d(C-H) = 0.96 Å and U iso (H) = 1.5U eq (C) for methyl group. The methyl groups were allowed to rotate but not to tip.  The molecular structure of the title compound with the atom numbering scheme, displacement ellipaoids are drawn at 30% probability level. H atoms are present as small spheres of arbitary radius.

Figure 2
The crystal packing of the title compound, viewed down a-axis, showing C11-H11···Cg1 i inter-molecular interactions.
The H atoms not involved in the bonding have been excluded for clarity. 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 > σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C6 0.0030 (