(2E)-1-(2,6-Dichloro-3-fluorophenyl)-3-phenylprop-2-en-1-one

In the title compound, C15H9Cl2FO, the F atom shows positional disorder over two positions, with site-occupancy factors of 0.747 (4) and 0.253 (4). The dihedral angle between the rings is 86.37 (10)°. In the crystal, C—H⋯O contacts connect the molecules into chains along the c axis. The shortest inter-centroid distance between two aromatic systems is 3.6686 (12) Å and is apparent between the halogenated rings.

In the title compound, C 15 H 9 Cl 2 FO, the F atom shows positional disorder over two positions, with site-occupancy factors of 0.747 (4) and 0.253 (4). The dihedral angle between the rings is 86.37 (10) . In the crystal, C-HÁ Á ÁO contacts connect the molecules into chains along the c axis. The shortest inter-centroid distance between two aromatic systems is 3.6686 (12) Å and is apparent between the halogenated rings.

Experimental
The fluorine atom on the halogenated phenyl ring shows rotational disorder over two positions with site occupancy factors of 0.75 and 0.25. The least-squares planes defined by the carbon atoms of the two aromatic moieties intersect at an angle of 86.37 (10)° (Fig. 1).
In the crystal, C-H···O contacts whose range falls by more than 0.1 Å below the sum of van-der-Waals radii of the respective atoms are present. These are supported by one of the vinylic hydrogen atoms and one of the hydrogen atoms of the unsubstituted phenyl ring. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for the hydrogen bonds is C 1 1 (5)C 1 1 (7) on the unary level. Metrical information about these contacts as well as their symmetry is summarized in Table 1. In total, the molecules are connected to chains along the crystallographic c axis. The shortest intercentroid distance between two aromtic systems was measured at 3.6686 (12) Å and is apparent between the halogenated phenyl rings (Fig. 2).
The packing of the title compound in the crystal structure is shown in Figure 3.

Experimental
To a stirred solution of 1-(2,6-dichloro-3-fluorophenyl)ethanone (1 g, 4.8 mmol) and benzaldehyde (0.51 g, 4.8 mmol) in ethanol (10 ml), powdered KOH (0.40 g 7.2 mmol) was added at 0 °C. The reaction mixture was stirred at room temperature for 2 h. After completion of the reaction, the mixture was pourred into ice cold water and subsequently acidified with 1.5 N HCl (pH ~3). The precipitated solid was filtered and dried to afford 1.2 g of the title compound as off-white solid in 86% yield. The single-crystal was grown from a mixture of toluene:acetone (v:v = 1:1) by slow evaporation at room temperature (m.p.: 385-388 K).

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H 0.95 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C).