(Z)-Ethyl 2-hydroxyimino-2-(4-nitrobenzyl)ethanoate

The title molecule, C11H10N2O6, has a Z conformation about the C=N bond of the oxime unit. There are significant twists from planarity throughout the molecule, the most significant being between the hydroxyimino and ester groups which are effectively orthogonal with an N—C—C—Ocarbonyl torsion angle of 91.4 (2)°. The crystal packing features oxime–benzoyl O—H⋯O contacts that lead to chains along [010] and C—H⋯O interactions also occur.

The title molecule, C 11 H 10 N 2 O 6 , has a Z conformation about the C N bond of the oxime unit. There are significant twists from planarity throughout the molecule, the most significant being between the hydroxyimino and ester groups which are effectively orthogonal with an N-C-C-O carbonyl torsion angle of 91.4 (2) . The crystal packing features oxime-benzoyl O-HÁ Á ÁO contacts that lead to chains along [010] and C-HÁ Á ÁO interactions also occur.

Comment
The title compound (I) was prepared as an intermediary during the synthesis of chiral hydroxyaminoacids and hydroxyaminoalcohols, as α-ketomethoxyimino compounds are reduced by sodium borohydride (Corrêa & Moran, 1999) and enantioselectively bio-reduced by whole cells of yeast (Kreutz et al., 1997;Kreutz et al., 2000).
The structure of (I) is non-planar as seen by the values of the C3-C4-C7-O3 and C4-C7-C8-N2 torsion angles within the central moiety of 8.8 (2) and 15.8 (2) °, respectively. The peripheral residues are twisted with respect to the inner atoms.
Thus, the nitro ring is twisted out of the plane of the benzene ring to which it is connected: the C2-C1-N1-O1 torsion angle is -13.7 (3) °. Even more dramatic is the twist about the C8-C9 bond with the C7-C8-C9-O6 torsion angle being 94.77 (17)°, indicating the terminal ester group is orthogonal to the hydroxyimino residue. With respect to the C8═N2 bond, the conformation is Z. There are two other structures in the literature containing the basic C(═O)C(═NOH)C(═O)OC framework. In benzyl 2-(hydroxyimino)acetoacetate a Z conformation is found for the oxime group (Forsyth et al., 2006) whereas in each of the two independent molecules comprising the asymmetric unit in ethyl 2-(hydroxyimino)-3-oxo-3-phenylpropionate, an E conformation is found (Ramos Silva et al., 2004).

The crystal packing of (I) is dominated by O-H···O hydrogen bonding involving the oxime-O4-H and benzoyl-O3
atoms which leads to the formation of supramolecular chains along [0 1 0] with a flat topology, Fig. 2 and Table 1. The presence of C-H···O contacts provide stability to the chain. These C5-H···O5 contacts close 13-membered {···OC 3 O···HC 4 NOH} synthons, Fig. 3 and Table 1. The chains are linked into 2-D arrays in the [3 0 1] plane by further C-H···O contacts involving the nitro groups and centrosymmetric 10-membered {···ONC 2 H} 2 synthons, Fig. 3 and Table 1. The resultant layer is essentially flat with the ethoxy groups lying above and below the layer. The methyl-H atoms of one of the disordered ethoxy groups form C-H···O contacts with the nitro-O1 atoms providing stability to the stacked layers, Fig. 4 and Table 1.

Experimental
The title compound, (I), was prepared following a modified literature method (Adkins and Reeve, 1938). A solution of sodium nitrite (5 mmol) and water (2 ml) was added drop-wise to a solution of ethyl 3-oxo-3-(4-nitrophenyl)propanoate (2 mmol) in glacial acetic acid (3 ml) at 273 K. The resulting solution was stirred for 1 h at 273 K. The temperature was then raised to 303 K and the reaction left for a further hour. The reaction mixture was quenched with water (2.5 ml) and treated with ether (4 x 5 ml). The organic layer was dried with Mg(SO 4 ) and the solvent evaporated to afford a mixture of Z:E (40:60) isomers in 87% yield that were separated by dissolving in ethyl acetate and precipitating with hexane.

Refinement
The O-and C-bound H atoms were geometrically placed (O-H = 0.82 Å and C-H = 0.9-0.97 Å) and refined as riding with U iso (H) = 1.2U eq (C) and 1.5U eq (O and methyl-C).
supplementary materials sup-2 Disorder was modelled for the ethyl group with two positions resolved for each of the C10 and C11 atoms. Fractional refinement (anisotropic) showed that the site occupancy factors were equal within experimental error and thus these were fixed at 0.5 in the final cycles of refinement. Fig. 1. Molecular structure of (I) showing atom labelling scheme and displacement ellipsoids at the 50% probability level (arbitrary spheres for the H atoms). Only one component of the disordered ethyl group is shown for reasons of clarity.