1-(4-Chlorophenyl)-3-(4-methoxyphenyl)-prop-2-en-1-one

Department of Physics, University College,Mangalore 575 001, IndiaCorrespondence e-mail:w.harrison@abdn.ac.ukKey indicatorsSingle-crystal X-ray studyT = 120 KMean (C–C) = 0.002 A˚R factor = 0.029wR factor = 0.071Data-to-parameter ratio = 16.3For details of how these key indicators wereautomatically derived from the article, seehttp://journals.iucr.org/e.Received 23 March 2006Accepted 24 March 2006

The geometrical parameters for the title compound, C 16 H 13 ClO 2 , are normal. Packing in a non-centrosymmetric space group, which is consistent with the non-zero second harmonic generation response, may be influenced by a C-HÁ Á ÁO interaction.

Comment
The title compound, (I) (Fig. 1), was prepared as part of our ongoing studies (Indira et al., 2002;Harrison et al., 2005Harrison et al., , 2006 of the non-linear optical (NLO) properties of chalcone derivatives (Uchida et al., 1998). The non-centrosymmetric, polar crystal structure of (I) is consistent with its significant second harmonic generation (SHG) response of 0.8 times that of urea (Watson et al., 1993).
An intermolecular C-HÁ Á ÁO hydrogen bond (Fig. 2) appears to help to assemble the molecules of (I) into helical stacks about the 2 1 screw axis, propagating in the polar [001] direction.
Experimental 4-Chloroacetophenone in ethanol (1.54 g, 0.01 mol) (25 ml) was mixed with 4-methoxybenzaldehyde (1.36 g, 0.01 mol) in ethanol (25 ml) and the mixture was treated with an aqueous solution of potassium hydroxide (20 ml, 5%). This mixture was stirred well and left to stand for 24 hr. The resulting crude solid mass was collected by filtration and recrystallized from ethanol, yielding clear blocks of (I).
We thank the EPSRC National Crystallography Service (University of Southampton) for the data collection. BKS  View of (I), showing 50% displacement ellipsoids (arbitrary spheres for the H atoms). The possible intramolecular C-HÁ Á ÁO interaction is indicated by a dashed line. 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.  (2)