(E)-3-(4-Methoxyphenyl)-3-[3-(4-methoxyphenyl)-1H-pyrazol-1-yl]prop-2-enal

In the title molecule, C20H18N2O3, the pyrazole ring forms a dihedral angle of 2.2 (1)° with its methoxyphenyl substituent and a dihedral angle of 67.2 (1)° with the benzene substituent on the propenal unit. In the crystal, molecules are connected by weak C—H⋯O hydrogen bonds, forming R 2 2(26) and R 2 2(28) cyclic dimers that lie about crystallographic inversion centres. These dimers are further linked through C—H⋯O and C—H⋯N hydrogen bonds, forming C(8), C(9), C(10) and C(16) chain motifs. These primary motifs are further linked to form secondary C 2 2(15) chains and R 2 2(18) rings.

In the title molecule, C 20 H 18 N 2 O 3 , the pyrazole ring forms a dihedral angle of 2.2 (1) with its methoxyphenyl substituent and a dihedral angle of 67.2 (1) with the benzene substituent on the propenal unit. In the crystal, molecules are connected by weak C-HÁ Á ÁO hydrogen bonds, forming R 2 2 (26) and R 2 2 (28) cyclic dimers that lie about crystallographic inversion centres. These dimers are further linked through C-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds, forming C(8), C(9), C(10) and C(16) chain motifs. These primary motifs are further linked to form secondary C 2 2 (15) chains and R 2 2 (18) rings.

D-HÁ
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL. Pyrazoles are classified as both aromatic ring compounds and heterocyclic compounds and are characterized by a 5membered ring structure composed of three carbon atoms and two nitrogen atoms in adjacent positions in the unsubstituted parent compound. Being so composed and having pharmacological effects on humans, they are classified as alkaloids although they are rare in nature. Pyrazole and its derivatives have been successfully tested for their antifungal (Chen & Li, 1998), antihistaminic (Mishra et al.,1998), anti-inflammatory (Smith et al., 2001, antiarrhythmic and sedative (Bruno et al., 1990), hypoglycemic (Cottineau et al., 2002), antiviral (Baraldi et al., 1998 and pesticidal (Londershausen, 1996) activities. Based on the above specifics and also as part of our continuing work on pyrazole related compounds (Susindran et al., 2010a(Susindran et al., ,b, 2012, we report here the structure of the title pyrazole derivative. The molecular structure of the title compound is shown in Fig. 1. The phenyl rings of the methoxyphenyl groups and the plane of the pyrazole ring form dihedral angles of 2.2 (1)° (with the C31-C36 ring) and 67.2 (1)° (with the C12-C17 ring). The crystal packing is stabilized through weak intermolecular C-H···O and C-H···N interactions (Table 1).

Experimental
Phosphorous oxychloride (0.024 mole) was added dropwise over 5 to 10 minutes to a mixture of 1-(4-methoxyphenyl)-1ethanone N-[(E)-1-(4-methoxyphenyl)ethylidene]hydrazone (0.003 mole) and 3 ml of dimethyl formamide cooled in ice to 0°C. The reaction mixture was then irradiated with microwaves for 30 sec. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was poured into crushed ice and extracted with dichloromethane. The organic layer was dried over anhydrous sodium sulfate. The products were separated by column chromatography using petroleum ether and ethyl acetate mixture (98/2 v/v) as eluent. The title compound was crystallized from dichloromethane.

Refinement
All the H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 -0.96 Å and U iso (H) = 1.2 -1.5 U eq (parent atom).

Figure 1
The molecular structure of the title compound with 50% probability displacement ellipsoids.

Figure 2
A view of the primary R 2 2 (26) and R 2 2 (28) rings and the secondary C 2 2 (15) chains.  A view of the C(8) chain extending along the a-axis.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.