(E)-1-(4-Decyloxyphenyl)-3-(2-hydroxyphenyl)prop-2-en-1-one

In the title compound, C25H32O3, the enone group adopts an s-cis conformation. The alkoxy chain is in an all-trans conformation. The dihedral angle between the benzene rings is 7.86 (5)°. In the crystal, molecules are connected by pairs of O—H⋯O hydrogen bonds, forming inversion dimers and giving R 2 2(10) rings. Within these dimers, weak C—H⋯O hydrogen bonds form two R 2 2(7) rings. In the crystal, the approximately planar molecules [largest deviation for an atom being 0.4737 (12) Å for the terminal C atom of the alkoxy chain] are arranged in sheets parallel to (20-1). Weak C—H⋯π interactions are also observed.

In the title compound, C 25 H 32 O 3 , the enone group adopts an scis conformation. The alkoxy chain is in an all-trans conformation. The dihedral angle between the benzene rings is 7.86 (5) . In the crystal, molecules are connected by pairs of O-HÁ Á ÁO hydrogen bonds, forming inversion dimers and giving R 2 2 (10) rings. Within these dimers, weak C-HÁ Á ÁO hydrogen bonds form two R 2 2 (7) rings. In the crystal, the approximately planar molecules [largest deviation for an atom being 0.4737 (12) Å for the terminal C atom of the alkoxy chain] are arranged in sheets parallel to (201). Weak C-HÁ Á Á interactions are also observed.  Satyanarayana et al. (2004). For related structures, see: Razak et al. (2009) ;Ngaini et al. (2010Ngaini et al. ( , 2011. For graph-set theory, see: Bernstein et al. (1995). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986). For standard bond-length data, see: Allen et al. (1987).  Table 1 Hydrogen-bond geometry (Å , ).
The alkoxy chain adopts an all trans conformation with the difference from the ideal values of the torsion angles ranging from 0.98 (7)° to 7.98 (9)°. The C16-O3-C13-C14 torsion angle of 4.73 (13)° indicate that atoms C16 and O3 and the attached benzene ring are approximately co-planar. The alkoxy chain appears to deviate from co-planarity with the ring for atoms further away i.e. C24 and C25. The dihedral angle between the least-square plane through atoms O3/C16-C25 [maximum deviation = 0.2507 (10)Å at C25] and the attached benzene ring is 15.20 (5)°.

Experimental
A mixture of 2-hydroxybenzaldehyde (2.44 ml, 20 mmol), 4-decyloxyacetophenone (6.65 g, 20 mmol) and KOH (4.04 g, 72 mmol) in methanol (60 ml) was heated at reflux for 12 h. The reaction was cooled to room temperature and acidified with cold diluted HCl (2N). After redissolving in hexane followed by few days of slow evaporation, crystals were collected.

Refinement
The O-bound H atom was located in a difference Fourier map and refined freely with O-H = 0.943 (17) Å. The remaining H atoms were placed in calculated positions with C-H = 0.93-0.97 Å. The U iso values were constrained to be 1.5U eq (methyl-H atom) and 1.2U eq (other H atoms). The rotating model group was applied for the methyl group.

Figure 1
The molecular structure of the title compound, showing 50% probability displacement ellipsoids.  The crystal packing, viewed along the b-axis, showing the molecules in pairs, arranged into sheets parallel to (201) plane.
Hydrogen bonds are shown as dashed lines. Only H atoms involved in hydrogen bonds are shown.  (Cosier & Glazer, 1986) operating at 100.0 (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. 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 > 2sigma(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.