(E)-1-(4-Chlorophenyl)-3-[4-(diethylamino)phenyl]prop-2-en-1-one

The asymmetric unit of the title chalcone derivative, C19H20ClNO, contains two independent molecules, which differ in the conformations of the ethyl groups in the diethylamino substituents. In the crystal, weak intermolecular C—H⋯O hydrogen bonds link molecules into ribbons propogating in [010]. The crystal packing also exhibits weak C—H⋯π interactions.


Comment
In continuation of our study of chalcone derivatives (Chantrapromma et al., 2009;Fun et al., 2009;Suwunwong et al., 2009) which can be used for fluorescence probe for sensing of DNA or proteins (Svetlichny et al., 2007;Xu et al., 2005), the title compound (I) was synthesized and its fluorescence with the maximum emission at 437 nm was measured. We report here its crystal structure.
The asymmetric unit of (I) contains two molecules, A and B, respectively, which differ in conformations of the ethyl groups of the diethylamino substituents. In molecule A, two ethyl groups are on the same side of the molecular plane, while they are on opposite sides in molecule B (Fig. 1). The bond lengths and bond angles in the two molecules are also slightly different. The molecules of (I) ( respectively. Weak intramolecular C9A-H9AA···O1A, C5B-H5BA···O1B and C9B-H9BA···O1B hydrogen bonds generate S(5) ring motifs (Bernstein et al., 1995). The bond distances in (I) are of normal values (Allen et al., 1987) and are comparable with those in the related structure (Chantrapromma et al., 2009).
In the crystal (Fig. 2), the 4-chlorophenyl and the pro-2-en-1-one units of the molecules are linked by weak intermolecular C-H···O hydrogen bonds (Table 1) resulting in the molecules being connected into ribbons propagating along the [0 1 0] direction. The crystal packing exhibits also weak C-H···π interactions (Table 1); Cg1 is the centroid of the C10B-C15B ring.

Experimental
The title compound was synthesized by the condensation of 4-chloroacetophenone (0.40 g, 3 mmol) with 4-diethylaminobenzaldehyde (0.5 g, 3 mmol) in ethanol (20 ml) in the presence of 20% NaOH (aq) (5 ml). After stirring for 3 hr at 278 K, the resulting yellow solid was obtained and then collected by filtration, washed with distilled diethyl ether, dried and purified by repeated recrystallization from acetone. Yellow block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystalized from methanol by the slow evaporation of the solvent at room temperature after several days, Mp. 374-375 K.
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic and CH, 0.97 Å for CH 2 and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.68 Å from C6B and the deepest hole is located at 0.65 Å from Cl1B. Fig. 1. Two independent molecules of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme.   Glazer, 1986) operating at 100.0 (1) K.

Figures
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.