N-(2-Methylphenyl)succinamic acid

In the crystal structure of the title compound, C11H13NO3, the conformations of the N—H and C=O bonds in the amide segment are anti to each other and that of the amide H atom is syn to the ortho-methyl group in the benzene ring. In the crystal, O—H⋯O interactions lead to carboxylic acid inversion dimers and intermolecular N—H⋯O hydrogen bonds link the molecules into infinite chains. In addition, the crystal structure exhibits intermolecular C—H⋯π interactions between one of the methyl H atoms and the benzene ring of neighbouring molecules.

In the crystal structure of the title compound, C 11 H 13 NO 3 , the conformations of the N-H and C O bonds in the amide segment are anti to each other and that of the amide H atom is syn to the ortho-methyl group in the benzene ring. In the crystal, O-HÁ Á ÁO interactions lead to carboxylic acid inversion dimers and intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into infinite chains. In addition, the crystal structure exhibits intermolecular C-HÁ Á Á interactions between one of the methyl H atoms and the benzene ring of neighbouring molecules.

Related literature
For our study of the effect of ring and side-chain substitutions on the crystal structures of anilides and for related structures, see: Gowda et al. (2007;2010); Jagannathan et al. (1994). For the modes of interlinking carboxylic acids by hydrogen bonds, see: Leiserowitz (1976 Table 1 Hydrogen-bond geometry (Å , ).
BSS thanks the University Grants Commission, Government of India, New Delhi, for the award of a research fellowship under its faculty improvement program.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LX2138).

Comment
As a part of studying the effect of ring and side chain substitutions on the crystal structures of anilides (Gowda et al., 2007;2010), the crystal structure of N-(2-methylphenyl)succinamic acid (I) has been determined. The conformations of N-H and C═O bonds in the amide segment are anti to each other. The conformation of the amide oxygen and the carbonyl oxygen of the acid segment are also anti to each other, similar to that observed in N-(2-chlorophenyl)succinamic acid (II) (Gowda et al., 2009), but contrary to the syn conformation observed in N-(3-methylphenyl)succinamic acid (III) (Gowda et al., 2010). Further, the conformation of both the C═O bonds are anti to the H atoms of their adjacent -CH 2 groups ( Fig. 1) and the C═O and O-H bonds of the acid group are in syn position to each other, similar to that observed in (II) and (III).
The conformation of the amide hydrogen is syn to the ortho-methyl group in the benzene ring, similar to that observed between the amide hydrogen and the ortho-Cl in (II), but contrary to the anti conformation observed between the amide hydrogen and the meta-methyl group in the benzene ring of (III). The intermolecular O-H···O and N-H···O hydrogen bonds pack the molecules into infinite chains in the structure (Table 1, Fig.2). Additionally, the crystal packing ( Fig. 2) is further stabilized by intermolecular C-H···π interactions between the methyl H atom and the benzene ring of neighbouring molecules, with a C11-H11A···Cg iii (Table 1; Cg is the centroid of the C1-C6 benzene ring). 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).

Experimental
The solution of succinic anhydride (0.01 mole) in toluene (25 ml) was treated dropwise with the solution of o-toluidine (0.01 mole) also in toluene (20 ml) with constant stirring. The resulting mixture was stirred for about one h 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 o-toluidine. The resultant solid N-(2-methylphenyl)-succinamic acid 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 by elemental analysis and characterized by its infrared and NMR spectra. The needle like colorless single crystals used in X-ray diffraction studies were grown in ethanolic solution by slow evaporation at room temperature.

Refinement
The H atom of the NH group was located in a difference map and its position refined with N-H = 0.82 (3) %A. The H atom of the OH group was located in a difference map and later restrained to the distance O-H = 0.82 (2) Å. The other H atoms were positioned with idealized geometry using a riding model with C-H = 0.93-0.97 Å. All H atoms were refined supplementary materials sup-2 with isotropic displacement parameters (set to 1.2 times of the U eq of the parent atom). O2 and O3 are slightly disordered and their U ij components were restrained to approximate isotropic behavoir. Fig. 1. Molecular structure of the title compound, showing the atom labelling scheme. The displacement ellipsoids are drawn at the 50% probability level. The H atoms are represented as small spheres of arbitrary radii.

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.