5-Ethyl-4-methyl-1H-pyrazol-3(2H)-one

In the title compound, C6H10N2O, the 2,3-dihydro-1H-pyrazole ring is approximately planar, with a maximum deviation of 0.013 (1) Å. Pairs of intermolecular N—H⋯O hydrogen bonds link neighboring molecules into dimers, generating R 2 2(8) ring motifs. These dimers are further linked into two-dimensional arrays parallel to the bc plane by intermolecular N—H⋯O hydrogen bonds. The crystal structure is further stabilized by C—H⋯π interactions.

In the title compound, C 6 H 10 N 2 O, the 2,3-dihydro-1Hpyrazole ring is approximately planar, with a maximum deviation of 0.013 (1) Å . Pairs of intermolecular N-HÁ Á ÁO hydrogen bonds link neighboring molecules into dimers, generating R 2 2 (8) ring motifs. These dimers are further linked into two-dimensional arrays parallel to the bc plane by intermolecular N-HÁ Á ÁO hydrogen bonds. The crystal structure is further stabilized by C-HÁ Á Á interactions.
In the crystal structure ( Fig. 1), the 2,3-dihydro-1H-pyrazole ring (C1-C3/N1/N2) is approximately planar with a maximum deviation of 0.013 (1) Å for atoms N1 and N2 (but they are on opposite sides of the plane). The bond lengths (Allen et al., 1987) and angles are within normal ranges and comparable to those in closely related structures reported recently (Shahani et al., 2009;2010).

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.