1-Methyl-3-trifluoromethyl-1H-pyrazol-5-ol

In the title compound, C5H5F3N2O, the F atoms are disordered over two sets of sites in a 0.64 (3):0.36 (3) ratio. In the crystal structure, O—H⋯N hydrogen bonds link the molecules into chains and a short C—H⋯F contact also occurs.

In the title compound, C 5 H 5 F 3 N 2 O, the F atoms are disordered over two sets of sites in a 0.64 (3):0.36 (3) ratio. In the crystal structure, O-HÁ Á ÁN hydrogen bonds link the molecules into chains and a short C-HÁ Á ÁF contact also occurs.

Comment
As part of the ongoing study of polyfluorinated heterocycles (Marcos & Martins, 2003), we report herein the crystal structure of the title compound.
In the molecule of the title compound (Fig 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges.
Ring A (C4-C9) is, of course, planar. The intramolecular C-H···O hydrogen bond (Table 1) results in the formation of a five-membered ring B (O1/C1-C3/H1A), having envelope conformation with C2 atom displaced by -0.668 (3) Å from the plane of the other ring atoms.
In the crystal structure, intermolecular O-H···N hydrogen bonds (Table 1) link the molecules (Fig. 2), in which they may be effective in the stabilization of the structure.
Experimental 4,4-Diethoxy-1,1,1-trifluorobut-3-en-2-one (2 mmol) was added to a stirred solution of hydrazine (2.2 mmol) at room temperature in ethanol (15 ml). The mixture was stirred under reflux for 24 h. The solvent was evaporated and to the residue was added H2O (10 ml) and the organic phase were extract with dichloromethane (15 ml). The organic extract was dried (Na 2 SO 4 ) and the solvent was removed under reduced pressure to obtain the title compound (yield; 25%, m.p. 446 K).
Colourless blocks of (I) were obtained by slow evaporation of an ethyl acetate solution.

Refinement
H atoms were positioned geometrically, with C-H = 0.93, 0.97 and 0.96 Å for aromatic, methylene and methyl H, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for all other H atoms. Fig. 1. The molecular structure of (I).

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.