1-(4-Bromophenyl)-3-(4-ethoxyphenyl)prop-2-en-1-one

The title compound, C17H15BrO2, consists of two substituted benzene rings connected by a prop-2-en-1-one group. The molecule is nearly planar and adopts an E configuration. The dihedral angle between the two benzene rings is 8.51 (19)°. The enone plane makes dihedral angles of 11.06 (19) and 7.69 (19)°, respectively, with the bromophenyl and ethoxyphenyl rings. The molecules are linked by C—H⋯O hydrogen bonds to form a zigzag ribbon-like structure along the b direction. The crystal structure is stabilized by weak intra- and intermolecular C—H⋯O interactions.


Comment
Chalcone and its derivatives have received much attention due to their interesting biological (Nel et al., 1998) and non-linear optical properties (Chopra et al., 2007;Sathiya Moorthi, Chinnakali, Nanjundan, Radhika et al., 2005;Sathiya Moorthi, Chinnakali, Nanjundan, Selvam et al., 2005;Schmalle et al., 1990;Wang et al., 2004;Gu, Ji, Patil, Dharmaprakash & Wang, 2008). Understanding the origin and magnitude of nonlinearity in such exotic molecules is very important from both a fundamental point of view and for its wide range of applications. Some chalcone derivatives exhibiting second harmonic generation (SHG) also possess other attributes such as transparency in the relevant wavelengths, ability to withstand laser irradiation, and chemical stability (Fichou et al., 1988;Goto et al., 1991;Uchida et al., 1998;Zhao et al., 2000). We previously reported the crystal structure of a related chalcone derivative, 1-(3-bromophenyl)-3-(4-ethoxyphenyl) prop-2-en-1-one, (II) (Fun et al., 2008). In our continuing systematic study, we report here the structure of the title compound, (I) which also crystallized in a non-centrosymmetric space group and, as with (II), it should exhibit second-order nonlinear optical properties.
The molecular structure of (I) (  (Bernstein et al., 1995). The overall conformation of (I) is flatter than that observed for (II) which can be attributed to the different positions of the Br substituent on ring A (para in (I) and meta in (II). The bond distances and angles in (I) have normal values and are comparable with a number of closely related structures (Fun et al., 2008;Patil, Ng et al., 2007).
In the crystal packing, the molecules are arranged in an anti-parallel manner and linked by weak C-H···O interactions (Table 1) into a zigzag ribbon-like structure along the b direction ( Fig. 2 and Fig. 3). Similar packing characteristics were observed in (II) (Fun et al., 2008). In (I) the same weak C-H···O (C16-H16B···O1) interaction is involved in the ribbonlinkage but there is also an additional weak C-H···O interaction which links the molecules (Table 1). This is also due to the different positions of the meta and para Br substitutions in (I) and (II) which made (I) more favourable for the C-H···O contacts.

Experimental
The title compound was synthesized by the condensation of 4-ethoxybenzaldehyde (0.01 mol, 1.39 ml) with 4-bromoacetophenone (0.01 mol, 1.99 g) in methanol (60 ml) in the presence of a catalytic amount of sodium hydroxide solution (5 supplementary materials sup-2 ml, 20%). After stirring for 3 h, the contents of the flask were poured into ice-cold water (500 ml) and left to stand for 4 h. The resulting crude solid was filtered and dried. Single crystals were obtained by recrystallization from acetone.

Refinement
All H atoms were placed in calculated positions, with C-H = 0.93 Å, U iso = 1.2U eq (C) for aromatic and CH, C-H = 0.97 Å, U iso = 1.2U eq (C) for CH 2 and C-H = 0.96 Å, U iso = 1.5U eq (C) for CH 3 atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.78 Å from Br1 and the deepest hole is located at 0.84 Å from Br1. Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids and the atom-numbering scheme. The dashed line represents the intra-molcular C-H···O interaction.

Special details
Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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