(E)-4-[(4-Methoxyphenyl)iminomethyl]-N,N-dimethylaniline

The title compound, C16H18N2O, an N-benzylideneaniline derivative with substituents on both aromatic rings, crystallizes with two independent molecules (A and B) in the asymmetric unit. Both molecules exist in the E configuration. The dihedral angle between the two aromatic rings is 8.20 (5)° for molecule A and 12.52 (6)° for molecule B, and the imino C—N torsion angle (τ) is 7.1 (2)° for molecule A and −14.7 (2)° for molecule B. In the crystal structure, molecules are arranged in stacks which propagate along the a-axis direction. The crystal structure is stabilized by a number of weak C—H⋯π interactions.


Related literature
For the conformational analysis of similar compounds, see: Bernstein et al. (1981); For the structures of related compounds, see: Clegg et al. (1996), Ahmet et al. (1994).

S1. Comment
Interest in the optical properties of N-benzylideneaniline derivatives is focused on potential applications, such as liquid crystalline and non-linear optical properties. The second harmonic generation properties have been widely studied (Clegg et al., 1996 and references therein). Bernstein et al. (1981) have shown by ab initio calculations on benzylideneaniline and related molecules, that rotations about the Ph-N bond of up to 45° from a planar conformation are stabilizing, while rotations about the Ph-C bond are destabilizing, and the most stable free-molecule conformation is non-planar. In contrast, benzylideneaniline derivatives with substituents on one or both aromatic rings display a range of conformations in the solid state (Clegg et al., 1996).
The asymmetric unit of the title compound contains two crystallographically independent molecules (A and B), as shown in Fig. 1. Both molecules exist in the E-configuration and their bond lengths and angles are comparable to those in related structures (Ahmet et al., 1994;Clegg et al., 1996). The dihedral angle between the two aromatic rings is 8.20 (5)° for molecule A and 12.52 (6)° for molecule B, and the imino C-N torsion angle (τ) is 7.05 (18)° in molecule A and -14.68 (18)° in molecule B (see Table 1). This slight difference in the conformation of the two molecules is illustrated by In the crystal structure molecules A and B (i.e. the mean planes through all the non-H atoms in each molecule) are inclinded to one another by 68.8 (5)°. The molecules pack in stacks along the a direction (Fig. 3), and the crystal structure is stabilized by a number of C-H···π interactions (Table 2).

S2. Experimental
The title compound  was prepared by the reaction of 4-dimethylaminobenzaldehyde (2 mmol) with 4-methoxyaniline (2 mmol) in absolute ethanol (10 ml) for one day at room temperature. The solvent was evaporated and the product was recrystallized from acteone, giving yellow block-like crystals suitable for X-ray analysis.

S3. Refinement
H atoms were included in calculated positions and treated as riding atoms: C-H = 0.95 -0.98 Å, with U iso = 1.2 or 1.5U eq (parent C-atom).