2-(4-Chlorophenyl)chromen-4-one

The title compound, C15H9ClO2, is a synthetic flavonoid obtained by the cyclization of 3-(4-chlorophenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one. The 4-chlorophenyl ring is twisted at an angle of 11.54° with respect to the chromen-4-one skeleton. In the crystal, pairs of molecules are interconnected by weak Cl⋯Cl interactions [3.3089 (10) Å] forming dimmers which are further peripherally connected through intermolecular C—H⋯O hydrogen bonds.


Related literature
The centroid-centroid distance between two parallel chromone ring in the molecule is 3.87 Å. Further, it is evident from the crystal packing structure (

Experimental
The synthesis of the title compound was carried out in two steps according to the published procedure. (Migrdichian 1957;Awasthi et al., 2009). In the first step, an aqueous solution of sodium hydroxide (10% w/v, 10 ml) was added to a solution of 2-hydroxyacetophenone (1.77 g m, 10 mmol) and 4-chlorobenzaldehyde (1.73 g m, 10 mmol) in minimum amount of methanol (3-5 ml) at ice cooled flask. The reaction mixture was allowed to draw closer to room temperature and stirred for 18-20 h yielded a yellow solid. The completion of the reaction was monitored by thin layer chromatography. After completion of the reaction, the mixture was neutralized with 10% hydrochloric acid in water. The compound was characterized by 1 H NMR, 13 C NMR, FT-IR and EI-MS.
In second step, the cyclization was carried out according to published procedure (Shah et al., 1955). Briefly, 3-(4chlorophenyl)-1-(2-hydroxyphenyl)propenone (40 mg, 0.12 mmol) & SeO 2 (39 mg, 0.35 mmol) were added to dry amyl alcohol (30 ml) and the mixture was heated in an oil bath at 140-150 °C so that the entire compound was completely dissolved in the solvent. The reaction mixture was refluxed for 12 h and completion of the reaction was monitored by TLC. For crystallization 5 mg of compound dissolved in 5 ml mixture of Petroleum ether/ethylacetate (80:20) and left for several days at ambient temperature which yielded fine needle shape crystals.

Refinement
All H atoms were located from Fourier map (range of C-H = 0.93 Å) allowed to refine freely.  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 Rfactors(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