(2E)-3-(6-Methoxynaphthalen-2-yl)-1-[4-(methylsulfanyl)phenyl]prop-2-en-1-one

The asymmetric unit of the title compound, C21H18O2S, consists of two crystallographically independent molecules (A and B). The molecules exist in a trans conformation with respect to the central C=C bond. The naphthalene ring system makes dihedral angles of 51.62 (12) (molecule A) and 52.69 (12)° (molecule B) with the benzene ring. In molecule A, the prop-2-en-1-one group forms dihedral angles of 22.84 (15) and 29.02 (12)° with the adjacent naphthalene ring system and benzene ring, respectively, whereas the corresponding angles are 30.04 (12) and 23.33 (12)° in molecule B. In the crystal, molecules are linked by intermolecular C—H⋯O hydrogen bonds into head-to-tail chains along the a axis. The crystal packing also features C—H⋯π interactions. The crystal studied was a pseudo-merohedral twin with twin law (100 0-10 00-1) and a refined component ratio of 0.6103 (16):0.3897 (16).

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  Chalcones are unsaturated ketones containing the reactive ketoethylenic group -CO-CH═CH-. These compounds are coloured due to the presence of the chromophore -CO-CH═CH-, and depends on the presence of other auxochromes. Several methods are available for the preparation of chalcones (Mori et al., 2003;Kumar et al., 2006). The most convenient method is the Claisen-Schimdt condensation of equimolar quantities of arylmethylketone with aryl aldehyde in the presence of alcoholic alkali (Amir et al., 2008). Chalcones are used to synthesize several derivatives like cyanopyridines, pyrazolines, isoxazoles and pyrimidines with different heterocyclic ring systems (Atwal et al., 1990). In view of the importance of chalcones, the title compound was synthesized and its crystal structure is reported herein.
The asymmetric unit of the title compound ( Fig. 1)  whereas the corresponding angles are 30.04 (12) and 23.33 (12)° in molecule B. Bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable to those found in a related structure (Kobkeatthawin et al., 2011).

Refinement
All H atoms were positioned geometrically [C-H = 0.93 and 0.96 Å] and refined using a riding model with U iso (H) = 1.2 or 1.5U eq (C). A rotating group model was applied to the methyl groups. The crystal was a pseudo-merohedral twin with twin law (100 010 001) and BASF of 0.3897 (16).

Figure 1
The molecular structure of the title compound with atom labels and 50% probability displacement ellipsoids.

Figure 2
The crystal packing of the title compound. Hydrogen atoms not involved in hydrogen bonding (dashed lines) have been omitted for clarity.

(2E)-3-(6-Methoxynaphthalen-2-yl)-1-[4-(methylsulfanyl)phenyl]prop-2-en-1-one
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.65 e Å −3 Δρ min = −0.37 e Å −3 Absolute structure: Flack (1983), 3893 Friedel pairs Flack parameter: 0.24 (8) Special details Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.