Ethyl 2-[(4-chlorophenyl)hydrazono]-3-oxobutanoate

The molecule of the title oxobutanoate derivative, C12H13ClN2O3, is nearly planar; the interplanar angle between the benzene ring and the mean plane through the hydrazono-3-oxobutanoate unit is 2.69 (3)°. An intramolecular N—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal packing, C—H⋯O(3-oxo) interactions link molecules into dimers. The dimers thus formed are linked through C—H⋯O(carboxylate C=O) interactions, leading to the formation of ribbons along the [01] direction, which are stabilized via Cl⋯Cl [3.2916 (3) Å] contacts. The ribbons are stacked via C⋯O contacts [3.2367 (12)–3.3948 (12) Å].

The molecule of the title oxobutanoate derivative, C 12 H 13 ClN 2 O 3 , is nearly planar; the interplanar angle between the benzene ring and the mean plane through the hydrazono-3-oxobutanoate unit is 2.69 (3) . An intramolecular N-HÁ Á ÁO hydrogen bond generates an S(6) ring motif. In the crystal packing, C-HÁ Á ÁO(3-oxo) interactions link molecules into dimers. The dimers thus formed are linked through C-HÁ Á ÁO(carboxylate C O) interactions, leading to the formation of ribbons along the [011] direction, which are stabilized via ClÁ Á ÁCl
In the crystal packing, the C5-H5A···O1 interactions link two molecules into a dimer (Table 1 and

Experimental
Compound (I) was prepared as reported in literature (Amir & Agarwal, 1997). 4-Chloroaniline (1.27 g, 10 mmol) was dissolved in dilute hydrochloric acid (11.0 ml) and cooled to 273 K in an ice bath. To this cold solution, sodium nitrite (1.6 g in 5.0 ml water) was added. The temperature of the reaction mixture was not allowed to raise above 323 K. The resulting diazonium salt solution was then filtered into a cooled solution of ethylacetoacetate (1.7 ml) and sodium acetate (3.5 g) in ethanol (50 ml). The resulting yellow solid was filtered, washed with ice-cold water, dried and recrystallized from methanol.

Refinement
All H atoms were placed in calculated positions with d(N-H) = 0.91 Å, d(C-H) = 0.93 Å for aromatic, 0.97 Å for CH 2 and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl-H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl substituents. Fig. 1. The structure of (I), showing 50% probability displacement ellipsoids and the atomnumbering scheme. The N-H···O hydrogen bond was drawn as a dashed line.

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