Ethyl 2-[(2,4-difluorophenyl)hydrazinylidene]-3-oxobutanoate

The asymmetric unit of the title compound, C12H12F2N2O3, contains two molecules, both of which exist in an E conformation with respect to their C=N bonds [1.321 (6) and 1.310 (6) Å]. The molecular conformations are supported by intramolecular N—H⋯O hydrogen bonds, which generate S(6) rings. In the crystal, molecules are linked by C—H⋯O and C—H⋯F hydrogen bonds into layers lying parallel to (001). The crystal studied was an inversion twin with a 0.58 (1):0.42 (1) domain ratio.

The asymmetric unit of the title compound, C 12 H 12 F 2 N 2 O 3 , contains two molecules, both of which exist in an E conformation with respect to their C N bonds [1.321 (6) and 1.310 (6) Å ]. The molecular conformations are supported by intramolecular N-HÁ Á ÁO hydrogen bonds, which generate S(6) rings. In the crystal, molecules are linked by C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds into layers lying parallel to (001). The crystal studied was an inversion twin with a 0.58 (1):0.42 (1) domain ratio.

Experimental
The title compound was prepared by dissolving 2,4-difluoroaniline (0.01 mol) in dilute hydrochloric acid (10 ml) and cooled to 273K in an ice bath. To this, a cold solution of sodium nitrite (0.02 mol) was added. The resulting diazonium salt solution was filtered into a cold solution of ethyl acetoacetate (0.05 mol) and sodium acetate in ethanol. The separated yellow solid was filtered, washed with water and recrystallized from ethanol. Yellow blocks of (I) were obtained from DMF by slow evaporation.

Refinement
Atoms H1NA and H1NB were located in a difference Fourier map and refined freely with N-H = 0.86 (6) and 0.92 (5) Å. The remaining H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.97 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. The crystal studied was an inversion twin with a 0.58 (1):0.42 (1) domain ratio. Fig. 1. The molecular structure of the title compound showing 30% probability displacement ellipsoids for non-H atoms. Intramolecular hydrogen bonds are shown as dashed lines.

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.   supplementary materials sup-9