(4Z)-4-[(2E)-1-Hydroxy-3-(4-methoxyphenyl)prop-2-enylidene]-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one

The title compound, C20H18N2O4, is a chalcone derivative of pyrazole. The pyrazole ring is inclined at a dihedral angle of 19.29 (12)° to the methoxyphenyl ring mean plane, and by 1.19 (13)° to the phenyl ring. The molecular structure is stabilized by an intramolecular O—H⋯O hydrogen bond, making an almost planar (r.m.s. deviation = 0.0243 Å) six membered ring.

The title compound, C 20 H 18 N 2 O 4 , is a chalcone derivative of pyrazole. The pyrazole ring is inclined at a dihedral angle of 19.29 (12) to the methoxyphenyl ring mean plane, and by 1.19 (13) to the phenyl ring. The molecular structure is stabilized by an intramolecular O-HÁ Á ÁO hydrogen bond, making an almost planar (r.m.s. deviation = 0.0243 Å ) six membered ring.

Experimental
The title compound was prepared according to the literature method (Konieczny et al., 2007). 1 mmol (0.216 g) of 3-methyl-1-phenyl-acetyl-5-hydroxy pyrazole and 1.5 mmol (0.204 g) of 4-methoxybenzaldehyde was added to the mixture of 2 ml of glacial acetic acid and 0.2 ml of concentrated sulfuric acid and heated at 353-358 K for 9 h with stirring. The progress of the reaction was followed by TLC. On completion, the mixture was added to ice cold water. The precipitate obtained was filtered off, washed with methanol and purified by column chromatography using n-hexane:ethyl acetate(3:2). Red needle-like crystals, suitable for X-ray analysis, were obtained by slow evaporation of a solution in chloroform at r.t.

Refinement
In the final cycles of refinement, in the absence of significant anomalous scattering effects, 672 Friedel pairs were merged and Δf " set to zero. The H-atoms were included in calculated positions and treated as riding: C-H = 0.93 Å for aromatic, C-H = 0.96 Å for CH 3 and O-H = 0.82 Å, with U iso (H) = k × U eq (parent C-or O-atom), where k = 1.2 for aromatic H-atoms and 1.5U eq (parent O-atom, and methyl C-atoms). Fig. 1. The molecular structure of the title compound, with thermal ellipsoids drawn at the 50% probability level. The intramolecular O-H···O hydrogen bond is shown as a dashed line.

Figures
supplementary materials

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.