4-Methyl-5-phenyl-1H-pyrazol-3(2H)-one

The asymmetric unit of the title compound, C10H10N2O, contains two crystallographically independent molecules with similar geometries, which exist in the keto form. The C=O bond lengths are 1.2878 (12) Å in molecule A and 1.2890 (12) Å in molecule B, indicating that the compound undergoes enol-to-keto tautomerism during the crystallization process. In molecule A, the pyrazole ring is approximately planar [maximum deviation = 0.007 (1) Å] and forms a dihedral angle of 36.67 (6)° with the attached phenyl ring. In molecule B, the dihedral angle formed between the pyrazole ring [maximum deviation = 0.017 (1) Å] and the phenyl ring is 41.19 (6)°. In the crystal, intermolecular N—H⋯O hydrogen bonds link neighbouring molecules into dimers generating R 2 2(8) ring motifs. These dimers are linked into ribbons along [101] via intermolecular N—H⋯O hydrogen bonds, forming R 4 2(10) ring motifs.

The asymmetric unit of the title compound, C 10 H 10 N 2 O, contains two crystallographically independent molecules with similar geometries, which exist in the keto form. The C O bond lengths are 1.2878 (12) Å in molecule A and 1.2890 (12) Å in molecule B, indicating that the compound undergoes enol-to-keto tautomerism during the crystallization process. In molecule A, the pyrazole ring is approximately planar [maximum deviation = 0.007 (1) Å ] and forms a dihedral angle of 36.67 (6) with the attached phenyl ring. In molecule B, the dihedral angle formed between the pyrazole ring [maximum deviation = 0.017 (1) Å ] and the phenyl ring is 41.19 (6) . In the crystal, intermolecular N-HÁ Á ÁO hydrogen bonds link neighbouring molecules into dimers generating R 2 2 (8) ring motifs. These dimers are linked into ribbons along [101] via intermolecular N-HÁ Á ÁO hydrogen bonds, forming R 4 2 (10) ring motifs.

Related literature
For background to pyrazole derivatives and their antimicrobial activity, see: Ragavan et al. (2009Ragavan et al. ( , 2010. For bondlength data, see: Allen et al. (1987). For the structure of the enol form of this molecule, see: Shahani et al. (2010). For other related structures, see: Loh et al. (2010a,b,c). For hydrogenbond motifs, see: Bernstein et al. (1995). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 Table 1 Hydrogen-bond geometry (Å , ).
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  Pyrazole derivatives also act as anti-angiogenic agents, A3 adenosine receptor antagonists, neuropeptide YY5 receptor antagonists as well as kinase inhibitors for the treatment of type 2 diabetes, hyperlipidemia, obesity and thrombopiotinmimetics. Recently urea derivatives of pyrazoles have been reported as potent inhibitors of p38 kinase. Since the high electronegativity of halogens (particularly chlorine and fluorine) in the aromatic part of the drug molecules plays an important role in enhancing their biological activity, we are interested to have 4-fluoro or 4-chloro substitution in the aryls of 1,5-diaryl pyrazoles.
These properties and applications are discussed in our previous reports on the synthesis of novel pyrazole derivatives and their microbial activities (Ragavan et al., 2009. The enol-form of this compound has been already reported in the literature (Shahani et al., 2010).
The title compound ( Fig. 1), consists of two crystallographically independent molecules, with similar geometries and exists in the keto-form. This indicates that the compound undergoes an enol-to-keto tautomerism during the crystallization process with the bond length of C═O being 1.2878 (12) (Allen et al., 1987) and angles are within the normal ranges and are comparable to the related structures (Loh et al., 2010a,b,c).

Experimental
The compound was synthesized using a literature method (Ragavan et al., 2009  remaining H atoms were positioned geometrically with bond lengths C-H = 0.93 to 0.96 Å and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model was applied to the methyl groups. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. 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.