N-(4-Chloro-2-methylphenyl)maleamic acid

In the molecular structure of the title compound, C11H10ClNO3, the conformation of the N—H bond in the amide segment is syn to the ortho-methyl group in the phenyl ring. The C=O and O—H bonds of the acid group are in the relatively rare anti position with respect to each other. This is an obvious consequence of the hydrogen bond donated to the amide carbonyl group. The central oxobutenoic acid core C(=O)—C=C—C—OH is twisted by 31.65 (6)° out of the plane of the 4-chloro-2-methylphenyl ring. An intramolecular O—H⋯O hydrogen bond occurs. In the crystal, N—H⋯O hydrogen bonds link the molecules into infinite chains running along the a axis.

In the molecular structure of the title compound, C 11 H 10 ClNO 3 , the conformation of the N-H bond in the amide segment is syn to the ortho-methyl group in the phenyl ring. The C O and O-H bonds of the acid group are in the relatively rare anti position with respect to each other. This is an obvious consequence of the hydrogen bond donated to the amide carbonyl group. The central oxobutenoic acid core C( O)-C C-C-OH is twisted by 31.65 (6) out of the plane of the 4-chloro-2-methylphenyl ring. An intramolecular O-HÁ Á ÁO hydrogen bond occurs. In the crystal, N-HÁ Á ÁO hydrogen bonds link the molecules into infinite chains running along the a axis.
The conformations of the N-H and the C=O bonds in the amide segment are anti to each other. But the conformation of the N-H bond is syn to the ortho-methyl group in the phenyl ring. In the maleamic acid moiety, the amide C=O bond is anti to the adjacent C-H bond, while the carboxyl C=O bond is syn to the adjacent C-H bond. The observed rare anti conformation of the C=O and O-H bonds of the acid group is similar to that observed in N-(2-methylphenyl)-maleamic acid (Gowda et al., 2010). This is an obvious consequence of the hydrogen bond donated to the amide carbonyl group. The central oxobutenoic acid core C(=O)-C=C-C-OH is twisted by 31.65 (6)° out of the plane of the 4-chloro-2-methylphenyl ring.
The various modes of interlinking carboxylic acids by hydrogen bonds is described elsewhere (Leiserowitz, 1976).
In (I), both the intramolecular O-H···O and intermolecular N-H···O hydrogen bonds have been observed. The packing of molecules linked by N-H···O hydrogen bonds into infinite chains running along the a-axis is shown in Fig. 2.

Experimental
The solution of maleic anhydride (0.025 mol) in toluene (25 ml) was treated dropwise with the solution of 4-chloro-2methylaniline (0.025 mol) also in toluene (20 ml) with constant stirring. The resulting mixture was stirred for about 30 min. and set aside for an additional 30 min. at room temperature for the completion of reaction. The mixture was then treated with dilute hydrochloric acid to remove the unreacted 4-chloro-2-methylaniline. The resultant solid N-(4-chloro-2methylphenyl)-maleamic acid was filtered under suction and washed thoroughly with water to remove the unreacted maleic anhydride and maleic acid. It was recrystallized to constant melting point from ethanol. The purity of the compound was checked by elemental analysis and characterized by its infrared spectra.
The plate like colorless single crystals of the title compound used in X-ray diffraction studies were grown in an ethanol solution by slow evaporation (0.5 g in about 30 ml of ethanol) at room temperature.

Refinement
All hydrogen atoms were placed in calculated positions with C-H distances of 0.93Å (C-aromatic) and 0.96Å (C-methyl), and constrained to ride on their parent atoms. Amide and O-H atoms were seen in difference map and were refined with supplementary materials sup-2 the N-H and O-H distances restrained to 0.86 (1)Å and 0.92 (1) Å, respectively. The U iso (H) values were set at 1.2 U eq (C-aromatic, N) or 1.5U eq (C-methyl). Fig. 1. Molecular structure of the title compound showing the atom labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.  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.