5-Amino-3-methyl-1,2-oxazole-4-carbonitrile

In the title compound, C5H5N3O, the isoxazole ring is essentially planar, with a maximum deviation of 0.007 (1) Å from the least-squares plane. The N atom of the amine group exhibits sp 2 character (sum of bond angles around this atom = 358°). In the crystal, molecules are aggregated by two kinds of N—H⋯N hydrogen bonds into fused R 2 2(12) and R 6 6(26) rings, forming a slightly puckered two-dimensional array lying parallel to (101).

In the title compound, C 5 H 5 N 3 O, the isoxazole ring is essentially planar, with a maximum deviation of 0.007 (1) Å from the least-squares plane. The N atom of the amine group exhibits sp 2 character (sum of bond angles around this atom = 358 ). In the crystal, molecules are aggregated by two kinds of N-HÁ Á ÁN hydrogen bonds into fused R 2 2 (12) and R 6 6 (26) rings, forming a slightly puckered two-dimensional array lying parallel to (101).
The title molecule (Fig. 1) exhibits a planar isoxazole ring with a maximum deviation of 0.007 (1) Å for atom C2. The sum of the bond angles around the N atom of the amine group (358°) is in accordance with sp 2 hybridization.
As has been described for related push-pull nitriles (Ziao et al., 2001;Hao et al., 2005), there is a conjugative interaction between the amino nitrogen lone pair and the nitrile nitrogen via the C1═C2 bond which increases the hydrogen-bonding acceptor capability of the nitrile nitrogen. Thus, the amino nitrogen lone pair is not available for a hydrogen-bond interaction and it does not form any hydrogen bond as an acceptor. In addition, the C4≡N3 bond length [1.1424 (16) Å] is typical of the nitrile bond lengths found in push-pull nitriles.

Experimental
To a solution of hydroxylamine hydrochloride (13.9 g, 0.2 mol) in 10% sodium hydroxide (80 ml), (1-ethoxyethylidene)malononitrile (27.23 g, 0.2 mol) was added dropwise at 323 K under vigorous stirring condition. The temperature was kept below 323 K by making this addition slowly and by addition of small amount of ice. After stirring for an additional 1.5 h at approximately 293 K, the resulting solid was filtered and washed with water. Single crystals of title compound were obtained from a solution of aqueous ethanol after slow evaporation at room temperature.

Refinement
All H atoms were located on a final ΔF map. The positions of H atoms from the methyl group were determined geometrically (C-H = 0.96 Å) and these atoms were refined as riding with U iso (H) = 1.5U eq (C). The H atoms of the amine group were freely refined.

Figure 1
The molecular structure of title compound, showing the atom-numbering scheme and displacement ellipsoids at the 50% probability level.  A view of two-dimensional structure in the title compound showing the R 2 2 (12) and R 6 6 (26) graph-set motifs, built from N -H···N hydrogen bonds (dashed lines).

5-Amino-3-methyl-1,2-oxazole-4-carbonitrile
Crystal data Primary atom site location: structure-invariant direct methods Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0631P) 2 + 0.0596P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.19 e Å −3 Δρ min = −0.16 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.