N-(2,6-Dichlorophenyl)succinamic acid

In the crystal of the title compound, C10H9Cl2NO3, the conformations of the amide O atom and the carbonyl O atom of the acid segment are anti to each other and to the H atoms on the adjacent –CH2 groups. The C=O and O—H bonds of the acid group are syn to one another. In the crystal, molecules are packed into infinite chains through intermolecular O—H⋯O and N—H⋯O hydrogen bonds.

In the crystal of the title compound, C 10 H 9 Cl 2 NO 3 , the conformations of the amide O atom and the carbonyl O atom of the acid segment are anti to each other and to the H atoms on the adjacent -CH 2 groups. The C O and O-H bonds of the acid group are syn to one another. In the crystal, molecules are packed into infinite chains through intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds.
BSS thanks the University Grants Commission, Government of India, New Delhi, for the award of a research fellowship under its faculty improvement program.

S1. Comment
The amide moiety is an important constituent of many biologically important compounds. As part of our studies into the substituent effects on the structures and other aspects of this class of compounds (Bhat & Gowda, 2000;Gowda et al., 2000Gowda et al., , 2009a, in the present work, the crystal structure of N-(2,6-dichlorophenyl)-succinamic acid (I) has been determined ( Fig. 1). The conformation of the amide O atom and the carbonyl O atom of the acid segment are anti to each other and are also anti to the H atoms attached to the adjacent C atoms (Fig.1). Further, C=O and O-H bonds of the acid group are syn to each other, similar to that observed in N-(2-chlorophenyl)-succinamic acid (Gowda et al., 2009a) and N-(2,6-dimethylphenyl)-succinamic acid (Gowda et al., 2009b).
In the structure, the intermolecular O-H···O and N-H···O hydrogen bonds pack the molecules into infinite chains (Table 1, Fig.2).
The modes of interlinking carboxylic acids by hydrogen bonds is described elsewhere (Leiserowitz, 1976). The packing of molecules involving dimeric hydrogen bonded association of each carboxyl group with a centrosymmetrically related neighbor has also been observed (Jagannathan et al., 1994).

S2. Experimental
A solution of succinic anhydride (0.01 mole) in toluene (25 ml) was treated dropwise with the solution of 2,6-dichloroaniline (0.01 mole) also in toluene (20 ml) with constant stirring. The resulting mixture was stirred for about one hour and set aside for an additional hour at room temperature for completion of the reaction. The mixture was then treated with dilute hydrochloric acid to remove the unreacted 2,6-dichloroaniline. The resultant title compound was filtered under suction and washed thoroughly with water to remove the unreacted succinic anhydride and succinic acid. It was recrystallized to constant melting point from ethanol. The purity of the compound was checked and characterized by its infrared and NMR spectra.
Colorless needle like single crystals used in X-ray diffraction studies were grown in ethanolic solution by slow evaporation at room temperature.

S3. Refinement
The H atoms were positioned with idealized geometry using a riding model with the aromatic C-H = 0.93 Å, methylene C-H = 0.97 Å, N-H = 0.86 Å and O-H = 0.82 Å, and were refined with isotropic displacement parameters (set to 1.2 times of the U eq of the parent atom).
The crystals available for X-ray analysis were of rather poor quality and weak scatterers at high theta value with very low intensity, resulting in relatively high R values. The crystal has 37.1% weak reflections.   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 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.