4-{2-[4-(Dimethylamino)phenyl]ethylidene}benzonitrile

In the crystal of the title compound, C17H16N2, molecules are linked by C—H⋯N hydrogen bonds, forming rings of graph-set motifs R 2 1(6) and R 2 2(10). The title molecule is close to planar, with a dihedral angle between the aromatic rings of 0.6 (1)°. Torsion angles confirm a conformational trans structure.

In the crystal of the title compound, C 17 H 16 N 2 , molecules are linked by C-HÁ Á ÁN hydrogen bonds, forming rings of graphset motifs R 2 1 (6) and R 2 2 (10). The title molecule is close to planar, with a dihedral angle between the aromatic rings of 0.6 (1) . Torsion angles confirm a conformational trans structure.

Comment
Polyene systems are often used as π conjugating units as they provide an effective pathway for the efficient push-pull charge transfer between the donor and acceptor groups (Blanchard-Desce et al., 1988). Stilbene materials are expected to have diverse applications in photochemistry, fluorescense and non linear optical (NLO) processes when donor-acceptor substituents are introduced in the phenyl rings in order to spread the conjugation over the whole molecule (Lapouyade et al., 1993;Papper et al., 1997). Spectroscopic properties of the title 4-dimethylamino-4-cyano-stilbene (DCS) system have been extensively studied (Daum et al., 1995;Kubicki, 2007). Nevertheless, a survey of the literature shows that crystallographic information of stilbene compounds is still rather scarce.
The main aim of this work is to present the molecular and crystal structure of the DCS, one of the best exponents of the stilbene series, to analyse its configuration, its C=C double bond and to show the supramolecular arranging of the system.
A perspective view of the molecule of the title compound, showing the atomic numbering scheme, is given in Fig. 1. The DCS molecule suffers a rotational disorder, atoms C9 and C10 were modeled as exchanged with a minor occupancy fraction refined to 39 (1)%. The dimethylamino group forms a dihedral angle of 20.9 (2)° with respect to its phenyl ring. The phenyl rings of the title structure is almost coplanar showing a dihedral angle of 0.6 (1)° between the planes of the rings. The phenyl rings are twisted out of the ethylene bond plane, and are defined by the torsion angles C16-C11=C10A-C9A and C10A=C9A-C6-C5 (Table 1). The C9A=C10A bond length is close to the reported value for the ethylene C=C bond length [1.330 (1) A°] (Craig et al., 2006). The title molecule shows a torsion angle C6 C9A C10A C11 equal to 177.4 (3)°a nd it also shows that the bond angles between the olefinic double bond and the two aromatic rings C6-C9A=C10A and C11-C10A=C9A are close to 120° (Table 1) indicating small repulsion between the aromatic rings. These values allow to define its configuration as trans.

Experimental
By means of Wittig reaction (Maryanoff & Reitz, 1989), the 4-dimethylamino-benzyl-triphenylphosphonium iodide was prepared. The title stilbene was obtained by the reaction of equimolar quantities of phosphonium salt and 4-cyano benzaldehyde (0.02 mol) in THF solution. The mixture was maintained with stirring under argon atmosphere. The reaction mixture was kept at 273 K and it was dropped with a solution of tert-butanol and potassium tert-butoxide. Crystals of suitable quality supplementary materials sup-2 for single-crystal X-ray diffraction were grown in chloroform. Thin layer chromatography (TLC) was used to confirm the structure of the individual compounds. IR spectra were recorded on a Shimadzu FT-IR 8400 spectrophotometer.

Refinement
The space group P 2 1 /n was uniquely assigned from the systematic absences. All H-atoms were located from difference maps and then they were treated as riding atoms [C aro -H= 0.93 A° and C sp3 -H= 0.96 A°, U iso (H)= 1.2U eq (C aro ), U iso (H)= 1.5U eq (C sp3 )).