But-2-enal 2,4-dinitrophenylhydrazone

In the title compound, C10H10N4O4, the but-2-enal chain is almost planar, the largest deviation from the mean plane being 0.013 (1) Å, and this plane makes a dihedral angle of 9.95 (24)° with the benzene ring,. Of the two nitro groups, one is twisted with respect to the benzene ring, making a dihedral angle of 5.7 (1)°, whereas the other is nearly in the plane of the benzene ring, with a twist angle of only 0.7 (1)°. This difference is related to the occurence of an intramolecular N—H⋯O hydrogen bond with the O atom of the less twisted nitro group. The NH group is also involved in a weak interaction with the same O atom of a symmetry-related molecule, thus forming a pseudo inversion dimer.

In the title compound, C 10 H 10 N 4 O 4 , the but-2-enal chain is almost planar, the largest deviation from the mean plane being 0.013 (1) Å , and this plane makes a dihedral angle of 9.95 (24) with the benzene ring,. Of the two nitro groups, one is twisted with respect to the benzene ring, making a dihedral angle of 5.7 (1) , whereas the other is nearly in the plane of the benzene ring, with a twist angle of only 0.7 (1) . This difference is related to the occurence of an intramolecular N-HÁ Á ÁO hydrogen bond with the O atom of the less twisted nitro group. The NH group is also involved in a weak interaction with the same O atom of a symmetry-related molecule, thus forming a pseudo inversion dimer.

Experimental
In the title compound, the but-2-enal chain is planar with the largest deviation from the mean plane being 0.013 (1)Å at C1. This plane makes a dihedral angle of 9.95 (24)° with the benzene ring, so the whole molecule is roughly planar (Fig. 1).
Of the the two nitro groups, one is twisted with respect to the benzene ring making a dihedral angle of 5.7 (1)° whereas the other is nearly in the plane of the benzene ring with a twist angle of only 0.7 (1)°. This difference is related to the occurence of an intramolecular hydrogen N-H···bond with the O atom of the less twisted nitro group (Table 1). The NH is also in weak intermolecular interaction with the same O atom of a symmetry related molecule building a pseudo dimer (Table 1, Fig. 2).
Bond lengths and bond angles are consistent with those of other dinitrophenylhydrazone derivatives (Ohba,1996;Bolte & Dill, 1998) Experimental 2,4-Dinitrophenylhydrazine (1 mmol, 0.198 g) was dissolved in anhydrous methanol, H 2 SO 4 (98% 0.5 ml) was added to this, the mixture was stirred for several minitutes at 351 K, but-2-enal (1 mmol 0.070 g) in methanol (8 ml) was added dropwise and the mixture was stirred at refluxing temperature for 2 h. The product was isolated and recrystallized in methanol, red single crystals of (I) was obtained after two weeks.

Refinement
H atoms were placed in calculated position and treated as riding with C-H= 0.93Å (aromatic), 0.96Å(methyl) and N-H=

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.