(E)-1-(Thiophen-2-yl)-3-(2,4,6-trimethoxyphenyl)prop-2-en-1-one

There are two crystallograpically independent molecules in the asymmetric unit of the title heteroaryl chalcone derivative, C16H16O4S, with slightly different conformations. The thienyl ring of one molecule is disordered over two positions, with a refined site-occupancy ratio of 0.713 (5):0.287 (5). The molecules are twisted: the dihedral angle between the thienyl and benzene rings is 9.72 (19)° in the ordered molecule, and 3.8 (4) and 2.1 (8)° for the major and minor components, respectively, in the disordered molecule. In both molecules, all three substituted methoxy groups are coplanar with the benzene ring to which they are attached. In each molecule, a weak intramolecular C—H⋯O interaction generates an S(6) ring motif. In the crystal structure, adjacent molecules are linked into a three-dimensional network by weak C—H⋯O interactions.

There are two crystallograpically independent molecules in the asymmetric unit of the title heteroaryl chalcone derivative, C 16 H 16 O 4 S, with slightly different conformations. The thienyl ring of one molecule is disordered over two positions, with a refined site-occupancy ratio of 0.713 (5):0.287 (5). The molecules are twisted: the dihedral angle between the thienyl and benzene rings is 9. 72 (19) in the ordered molecule, and 3.8 (4) and 2.1 (8) for the major and minor components, respectively, in the disordered molecule. In both molecules, all three substituted methoxy groups are coplanar with the benzene ring to which they are attached. In each molecule, a weak intramolecular C-HÁ Á ÁO interaction generates an S(6) ring motif. In the crystal structure, adjacent molecules are linked into a three-dimensional network by weak C-HÁ Á ÁO interactions.

Comment
Chalcones have been reported to be responsible for a variety of biological activities such as analgesic, anti-inflammatory, antibacterial and antimycotic (Go et al., 2005;Liu et al., 2008;Ni et al., 2004) as well as HIV-1 protease inhibitory (Tewtrakul et al., 2003) and tyrosinase inhibitory (Ng et al., 2009) properties. Our research on the fluorescent and biological studies of chalcones and heteroaryl chalcone derivatives (Chantrapromma et al., 2009;Suwunwong et al., 2009Suwunwong et al., , 2011 led us to synthesize the title heteroaryl chalcone (I). (I) exhibits fluorescent property (Suwunwong et al., 2011) and possess moderate analgesic property. It was also tested for antibacterial activities but found to be inactive. Herein we report the crystal structure of (I).
There are two crystallographic independent molecules A and B in the asymmetric unit of (I) with different conformations of the methoxy group at para position or at atom C11 and also in bond angles ( B. This also indicates that the methoxy group at the para position (or at atom C11) has different conformations as it points toward the methoxy group at the ortho position at atom C13 (in molecule A) whereas it points toward the ortho methoxy at atom C9 (in molecule B). In each molecule, intramolecular C-H···O weak interaction (Table 1) generates S(6) ring motif (Bernstein et al., 1995). The bond distances agree with the literature values (Allen et al., 1987) and are comparable with those observed in related structures (Chantrapromma et al., 2009;Fun et al., 2010Fun et al., , 2011Suwunwong et al., 2009).
In the crystal packing ( Fig. 2), adjacent molecules are linked into a three-dimensional network by weak C-H···O interactions (Table 1).

Experimental
The title compound was synthesized by the condensation of 2,4,6-trimethoxybenzaldehyde (0.40 g, 2 mmol) with 2-acethylthiophene (0.35 ml, 2 mmol) in ethanol (30 ml) in the presence of 30% NaOH (aq) (5 ml). After stirring for 3 h in ice bath at 278 K, the resulting pale-yellow solid was collected by filtration, washed with distilled water, dried in air and purified by recrystallization from acetone. Pale-yellow needle-shaped single crystals of the title compound suitable for X-ray structure supplementary materials sup-2 determination were recrystallized from acetone-ethanol (1:1 v/v) by slow evaporation of the solvent at room temperature after several days; m.p. 381-382 K.

Refinement
All H atoms were placed in calculated positions, with C-H = 0.93 Å, U iso = 1.2U eq (C) for aromatic and methyne C atoms and C-H = 0.96 Å, U iso = 1.5U eq (C) for methyl groups. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 1.65 Å from C3 and the deepest hole is located at 0.29 Å from S1A. The thienyl ring of molecule B is disordered over two sites with refined site occupancies of 0.713 (5) and 0.287 (5). Initially SAME, DELU and SIMU restraints were used. In the final refinement, these restraints were removed. A total of 3389 Friedel pairs were used to determine the absolute structure.  (E)-1-(Thiophen-2-yl)-3-(2,4,6-trimethoxyphenyl)prop-2-en-1-one

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 120.0 (1) K.
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.