4-(4-Iodoanilino)-2-methylene-4-oxobutanoic acid

In the title compound, C11H10INO3, an addition product of itaconic acid anhydride and 4-iodoaniline, the least-squares planes defined by the atoms of the aromatic moiety and the non-H atoms of the carboxylic acid group enclose an angle of 74.82 (11)°. In the crystal, classical O—H⋯O hydrogen bonds formed by carboxylic groups, as well as N—H⋯O hydrogen bonds formed by amide groups, are present along with C—H⋯O contacts. Together, these connect the molecules into dimeric chains along the b-axis direction.

In the title compound, C 11 H 10 INO 3 , an addition product of itaconic acid anhydride and 4-iodoaniline, the least-squares planes defined by the atoms of the aromatic moiety and the non-H atoms of the carboxylic acid group enclose an angle of 74.82 (11) . In the crystal, classical O-HÁ Á ÁO hydrogen bonds formed by carboxylic groups, as well as N-HÁ Á ÁO hydrogen bonds formed by amide groups, are present along with C-HÁ Á ÁO contacts. Together, these connect the molecules into dimeric chains along the b-axis direction.
The C=C bond is present as its anti-Saytzeff tautomer. The N-C(=O) bond length of 1.351 (2) Å is indicative of amidetype resonance. The least-squares plane defined by the atoms of the aromatic moiety on the one hand and the nonhydrogen atoms of the carboxylic acid group on the other hand enclose an angle of 74.82 (11) ° ( Fig. 1).
In the crystal, C-H···O contatcs whose range falls by more than 0.1 Å below the sum of van-der-Waals radii are observed next to classical hydrogen bonds of the N-H···O and C-H···O type. The N-H···O hydrogen bonds are supported by the carbonyl oxygen atom of the amide functionality as acceptor. Simultaneously, one of the hydrogen atoms of the methylene group forms a C-H···O contact to the same oxygen atom which, therefore, acts as twofold acceptor. The carboxylic acid groups engage in the common dimeric hydrogen bonding pattern frequently encountered for many carboxylic acids. In total, the molecules are connected to dimeric chains along the crystallographic b axis. Metrical parameters as well as information about the symmetry of these contacts are summarized in Table 1. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for these contacts is C 1 1 (4)C 1 1 (4)R 2 2 (8) on the unary level. The shortest intercentroid distance between two aromatic systems was found at 4.7863 (11) Å which is about the length of axis b (Fig.   2).
The packing of the title compound in the crystal structure is shown in Figure 3.

Experimental
Itaconic anhydride (0.112 g, 1 mmol) was dissolved in acetone (30 ml) and 4-iodoaniline (0.219 g, 1 mmol) was added in small portions under stirring at room temperature over a timespan of 30 minutes. The mixture turned into a yellow slurry.
Stirring was continued for 1.5 h after which the slurry was filtered and the solid obtained was washed with acetone and dried to yield the title compound. Single crystals suitable for the X-ray diffraction study were grown from methanol by slow evaporation at room temperature.

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H 0.95 Å for aromatic and vinylic carbon atoms, C-H 0.99 Å for methylene groups) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C). The H atom of the hydroxyl group was allowed to rotate with a fixed angle around the C-O bond to best fit the experimental electron density (HFIX 147 in the SHELX program suite (Sheldrick, 2008)), with U(H) set to 1.5U eq (O). The nitrogen-bound H atom was located on a difference Fourier map and refined freely.