1-(4-tert-Butylbenzyl)-3-phenyl-1H-pyrazole-5-carboxylic acid

In the title compound, C21H22N2O2, the mean plane of the pyrazole ring makes dihedral angles of 18.80 (12) and 77.13 (5)°, respectively, with the mean planes of the phenyl and tert-butylbenzyl rings. The carboxylate group is inclined at 8.51 (14)° with respect to the pyrazole ring. The crystal structure displays intermolecular O—H⋯O hydrogen bonding, generating centrosymmetric dimers.

In the title compound, C 21 H 22 N 2 O 2 , the mean plane of the pyrazole ring makes dihedral angles of 18.80 (12) and 77.13 (5) , respectively, with the mean planes of the phenyl and tert-butylbenzyl rings. The carboxylate group is inclined at 8.51 (14) with respect to the pyrazole ring. The crystal structure displays intermolecular O-HÁ Á ÁO hydrogen bonding, generating centrosymmetric dimers.   Table 1 Hydrogen-bond geometry (Å , ).

References
Bruker ( The pyrazole unit is one of the core structures in a number of natural products. Many pyrazole derivatives are known to exhibit a wide range of biological properties such as antitumor (Wei et al., 2006). As a part of our continuing project on the study of synthesis and bioactivity evaluation of pyrazole derivatives (Xia et al., 2007b;Zhao et al., 2008;Zhang et al., 2008), we report here the synthesis and crystal structure of the title compound.
In the title compound ( Fig. 1), the pyrazole ring makes dihedral angles of 18.80 (12) and 77.13 (5)° with the phenyl and tert-butylbenzyl rings, respectively. The oxalate group is inclined at 8.51 (14)° with respect to the pyrazole ring. The crystal structure displays a strong intermolecular interaction which leads to the formation of hydrogen bonded dimeric units (Table   1) about inversion centers which is typical of organic carboxylic acids (Ding et al., 2007). The crystal structures of a few related compounds have been reported from our laboratory, e.g. (Ding et al., 2007;Xia et al., 2007a;Tang et al., 2007) Experimental A mixture of ethyl 1-(4-tert-Butylbenzyl)-3-phenyl-1H-pyrazole-5-carboxylate (0.01 mol) and potassium hydroxide (0.02 mol) in ethanol (40 ml) was heated to reflux for 3 h. The solvent was removed under reduced pressure and the residue was dissolved in water and acidified with hydrochloric acid (10%). The precipitate was filtered and dried to give a white solid (yield 92%). Crystals of (I) suitable for X-ray diffraction were obtained by slow evaporation of a solution of the solid in acetone at room temperature for 3 d.

Refinement
All H atoms were placed in calculated positions,with O-H = 0.82 Å and C-H = 0.93-0.97 Å, and included in the final cycles of refinement using a riding model, with U iso (H) = 1.2U eq (C) for aryl and methylene H atoms or 1.5U eq (C/O) for methyl and hydroxyl H atoms.
Figures Fig. 1. The molecular structure of (I), with displacement ellipsoids drawn at the 30% probability level.

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 > σ(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.