N-(2-Methylphenyl)maleamic acid

In the title compound, C11H11NO3, the conformation of the N—H bond is anti to the C=O bond in the amide segment, while it is syn to the ortho-methyl group in the phenyl ring. In the maleamic acid unit, 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 C=O and O—H bonds of the acid group are in the relatively rare anti position to each other. This is an obvious consequence of the intramolecular O—H⋯O hydrogen bond donated to the amide carbonyl group. The ortho-substituted phenyl ring makes a dihedral angle of 12.7 (1)° with the mean plane of the maleamic acid unit. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into zigzag chains parallel to [001]. These chains are further linked into sheet by weak π–π interactions [centroid–centroid distance = 3.425 (2) Å].

In the title compound, C 11 H 11 NO 3 , the conformation of the N-H bond is anti to the C O bond in the amide segment, while it is syn to the ortho-methyl group in the phenyl ring. In the maleamic acid unit, 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 C O and O-H bonds of the acid group are in the relatively rare anti position to each other. This is an obvious consequence of the intramolecular O-HÁ Á ÁO hydrogen bond donated to the amide carbonyl group. The ortho-substituted phenyl ring makes a dihedral angle of 12.7 (1) with the mean plane of the maleamic acid unit. In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into zigzag chains parallel to [001]. These chains are further linked into sheet by weakinteractions [centroid-centroid distance = 3.425 (2) Å ].
MT and JK thank the Grant Agency of the Slovak Republic (VEGA 1/0817/08) and the Structural Funds, Interreg IIIA, for financial support in purchasing the diffractometer. K. thanks the University Grants Commission, Government of India, New Delhi, for the award of a research fellowship under its faculty improvement program.

Comment
The amide moiety is an important constituent of many biologically significant compounds. As a part of studying the effect of ring and side chain substitutions on the crystal structures of this class of compounds (Gowda et al., 2009a,b,c;Prasad et al., 2002), the crystal structure of N-(2-methylphenyl)-maleamic acid (I) has been determined ( Fig. 1). 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 obsrved in N-(2,6-dimethylphenyl)-maleamic acid (Gowda et al., 2009a), N-(3,4-dimethylphenyl)-maleamic acid (Gowda et al., 2009b) and N-(2,4,6-trimethylphenyl)-maleamic acid (Gowda et al., 2009c).
The ortho-substituted phenyl ring makes a dihedral angle of 12.7 (1)° with the mean plane of the maleamic acid moiety (atoms C1, C2, C3, C4, N1, O1, O2 and O3). The orientation of the central amide group -NHOC-with respect to the phenyl ring is partially affected by the intramolecular hydrogen bond C10-H10···O1(amide) and is given by the torsion angle C10-C5-N1-C1 = -17.3 (2)°. Short intramolecular hydrogen bond O-H···O (Table 1) is important characteristic of the maleamic acid moiety. The C2-C3 bond length of 1.330 (2)Å clearly indicates the double bond character. In the crystal structure, the intermolecular N-H···O hydrogen bonds, having the amide N1 atom as donor and carbonyl O3 atom of the carboxyl group as acceptor, link the molecules into zigzag chains running along the [0 0 1] direction. Due to weak π-π interaction between the phenyl and maleamic acid moieties the chains are assembled to form sheets parallel to the bc-plane.
One mode of the chain coupling is shown in Fig. 2 as a short contact between the phenyl ring centroid Cg and the C4 atom of the carboxylic group at (-x,-y + 1,-z + 1).
The various 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 maleic anhydride (0.025 mol) in toluene (25 ml   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.