(2E)-1-[2-Hydroxy-4-(2-methylpropoxy)phenyl]-3-(4-methylphenyl)prop-2-en-1-one

The benzene rings in the title compound, C20H22O3, form a dihedral angle of 10.39 (8)°. Overall, the molecule is approximately planar with the exception of one of the terminal methyl groups; excluding this group, the r.m.s. deviation for the remaining 22 non-H atoms is 0.0968 Å. The conformation about the C=C bond is E, and an intramolecular O—H⋯O hydrogen bond leads to the formation of an S(6) motif. In the crystal, linear supramolecular chains are formed along the a axis via C—H⋯O contacts, and these are connected into double chains via C—H⋯π interactions.

With the exception of the methyl-C19 atom, the molecular structure, Fig Table 1, which closes an S(6) motif.
In the crystal packing, both C-H···O and C-H···π interactions are observed. Linear supramolecular chains aligned along the a axis are mediated by C-H···O contacts, Fig. 2 and Table 1. Centrosymmetrically related pairs of these chains are connected into a double chain via C-H···π contacts formed between the methylene-C17-H and the ring centroid of the tolyl ring, Fig. 3 and Table 1.
Semi-empirical Quantum Chemical Calculations were performed on (I) using the MOPAC2009 program (Stewart, 2009) to optimize the structure with the Parameterization Model 6 (PM6) approximation together with the restricted Hartree-Fock closed-shell wavefunction. Minimizations were terminated at an r.m.s. gradient of less than 0.01 kJ mol-1 Å -1 . The geometry optimised structure displays a significant difference in the relative orientation of the tolyl ring compared with the experimental structure. This is quantified by the value of the C6-C5-C8-C9 torsion angle of 150.7 compared with the experimental value of 179.72 (15) °. This change is related to the participation of this ring in the C-H···π contact as discussed above.

Experimental
A mixture of 2-hydroxy-4-isobutoxy acetophenone (0.01 mol) and 4-methyl benzaldehyde (0.01 mol) in ethanol (40 ml) were placed in a 250 ml round bottom flask and the resulting solution stirred at room temperature. After the solution became clear, a solution of potassium hydroxide (40%, 40 ml) was added slowly with constant stirring followed by stirring at room temperature for a further 20 h. After the completion of reaction, as indicated by TLC, the contents were poured onto crushed ice and acidified with dilute HCl (10%). The solid separated and was washed with water, filtered, and the crude product supplementary materials sup-2 was crystallized from methanol to obtain (I) in 90 % yield; m.pt. 417 K. The yellow needles were obtained by the slow evaporation of a methanol solution of (I).

Refinement
The H atoms were placed geometrically (O-H = 0.83 Å and C-H = 0.93-0.98 Å) and refined as riding with U iso (H) = 1.2-1.5U eq (parent atom). Fig. 1. The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.  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 > 2σ(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.