Ethyl 2-[2-(3-methoxyphenyl)hydrazinylidene]-3-oxobutanoate

The title compound, C13H16N2O4, is approximately planar (r.m.s. deviation = 0.065 Å for the 19 non-H atoms). An intramolecular N—H⋯O hydrogen bond generates an S(6) ring motif and the molecule adopts an E conformation with respect to the central C=N double bond. In the crystal, pairs of intermolecular C—H⋯O hydrogen bonds link adjacent molecules into inversion dimers. The crystal structure also features weak C—H⋯π interactions.

The title compound, C 13 H 16 N 2 O 4 , is approximately planar (r.m.s. deviation = 0.065 Å for the 19 non-H atoms). An intramolecular N-HÁ Á ÁO hydrogen bond generates an S(6) ring motif and the molecule adopts an E conformation with respect to the central C N double bond. In the crystal, pairs of intermolecular C-HÁ Á ÁO hydrogen bonds link adjacent molecules into inversion dimers. The crystal structure also features weak C-HÁ Á Á interactions.

Experimental
The title compound was prepared by dissolving 3-methoxy aniline (0.01 mol) in dilute hydrochloric acid (10 ml) and cooled to 0 °C 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 to yield yellow blocks of (I).

Refinement
Atom H1N1 was located in a difference Fourier map and refined freely with N-H = 0.871 (19) Å. The remaining H atoms were positioned geometrically with C-H = 0.93-0.97 Å. 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 groups.

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.