Crystal structure of (2E)-3-(3-ethoxy-4-hydroxyphenyl)-1-(4-hydroxyphenyl)prop-2-en-1-one

In the title compound, C17H16O4, the dihedral angle between the benzene rings is 21.22 (1)° and the mean plane of the prop-2-en-1-one group makes dihedral angles of 10.60 (1) and 11.28 (1)°, respectively, with those of the hydroxyphenyl and ethoxyphenyl rings. The ethoxy substituent forms a dihedral angle of 88.79 (2)° with the the prop-2-en-1-one group, which is found to be slightly twisted. In the crystal, phenolic O—H⋯O hydrogen bonds to the carbonyl O atom form a two-dimensional supramolecular network structure lying parallel to (010).


S1. Comment
Chalcones belonging to the flavonoid family constitute an important group of natural products due to their unforseen pharmacological potential. Chemically they consist of open-chain flavonoids in which the two aromatic rings are joined by a three-carbon α,β-unsaturated carbonyl system. The radical quenching properties of the phenolic groups present in many chalcones have raised interest in using the compounds or chalcone-rich plant extracts as drugs or food preservatives. Chalcones have been reported to possess many exciting activities which include anti-inflammatory, antimicrobial, antifungal, antioxidant, cytotoxic, anti-tumor and anticancer (Nowakowska, 2007). A number of chalcones having hydroxy or alkoxy groups in different position have been observed to possess vasodilatory (Ram et al., 2000), antimitotic (Khatib et al., 2005) and antimalarial activities (Papo & Shai, 2003).  (Table 1).
In the crystal packing (Fig. 2), the molecule are linked through hydroxyl O1-H···O4 i and O3-H···O4 ii hydrogen bonds to the carbonyl O-atom acceptor (Table 1). Atom O4 acts as a tricentre being involved also in the previously mentioned intramolecular interaction with C7-H7. The overall structure is a two-dimensional supramolecular network lying parallel to (010).

S2. Experimental
This is the acid catalyzed Claisen-Schmidt reaction and the procedure (Sidharthan et al., 2012;Chitra et al., 2013;Sathya et al., 2014) adopted in the synthesis of the typical chalcone diol is represented here. Dry HCl gas was passed for one hour through a well cooled and stirred solution of 4-hydroxyacetophenone (0.05 mol) and 4-hydroxy-3-ethoxybenzaldehyde (0.05 mol) in 120 mL of absolute alcohol in a 250 mL round-bottomed flask. A wine red coloured solution was formed. On addition of a sufficient quantity of ice cold water, a yellow precipitate of (2E)-3-(4-hydroxy-3-ethoxyphenyl)-1-(4-hydroxyphenyl)prop-2-en -1-one was formed, which was filtered, then washed with double distilled water and finally allowed to dry. The dried product was re-crystallized from hot ethanol: yield 80%.

S3. Refinement
Hydrogen atoms were positioned geometrically and treated as riding on their parent atoms, with C-H distances of 0.93 Å, O-H distances of 0.82 Å with U iso (H)= 1.5 U eq (c-methyl) and U iso (H)= 1.2Ueq(C) for other H atom.

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 30% probability level. The packing of the molecules in the unit cell. Non-associative H-atoms are omitted and dashed lines indicate hydrogen bonds. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.74 e Å −3 Δρ min = −0.43 e Å −3 Special details 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.