N,N′-Bis(3-methylphenyl)propanediamide

The molecular structure of the title compound, C17H18N2O2, is symmetrical around the central C atom. The two halves of the molecule are related by a twofold rotation axis. In each half of the molecule, the structure is stabilized by intramolecular C—H⋯O hydrogen bonds. Furthermore, each amide group is almost coplanar with the adjacent benzene ring [dihedral angle is 9.2 (2)°]. The planes of the amide groups are inclined at an angle of 68.5 (1)°, while the two benzene rings make a dihedral angle of 70.40 (3)°. In the crystal, molecules are linked by intermolecular N—H⋯O hydrogen bonds into chains running along the c axis. Neighbouring chains are weakly coupled by π–π stacking interactions [centroid–centroid distance = 3.7952 (8) Å].

The molecular structure of the title compound, C 17 H 18 N 2 O 2 , is symmetrical around the central C atom. The two halves of the molecule are related by a twofold rotation axis. In each half of the molecule, the structure is stabilized by intramolecular C-HÁ Á ÁO hydrogen bonds. Furthermore, each amide group is almost coplanar with the adjacent benzene ring [dihedral angle is 9.2 (2) ]. The planes of the amide groups are inclined at an angle of 68.5 (1) , while the two benzene rings make a dihedral angle of 70.40 (3) . In the crystal, molecules are linked by intermolecular N-HÁ Á ÁO hydrogen bonds into chains running along the c axis. Neighbouring chains are weakly coupled bystacking interactions [centroidcentroid distance = 3.7952 (8) Å ].
MT and JK thank the Grant Agency of the Slovak Republic (VEGA 1/0817/08) and Structural Funds, Interreg IIIA, for financial support in purchasing the diffractometer. VZR thanks the University Grants Commission, Government of India, New Delhi for the award of a research fellowship.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BQ2245).

Comment
The amide moiety is an important constituent of many biologically important compounds. As a part of studying the substituent effects on the structures of this class of compounds (Gowda et al., 2007;2010), the crystal structure of N,Nbis(3-methylphenyl)-propanediamide has been determined (I) (Fig. 1).
The molecule of (I) is symmetrical around the central carbon atom C8. The two halves of the molecule are related by the symmetry (-x + 1,y,-z + 1/2), which is a twofold rotation axis. The molecular structure is stabilized by the C-H···O intramolecular hydrogen bond in each half of the molecule (Table 1). In the geometry of the molecule, each amide group is almost coplanar with the adjacent phenyl ring, as indicated by the dihedral angle of 9.2 (2)°. The planes of amide groups are inclined at an angle of 68.5 (1)°, while the two phenyl rings make a dihedral angle of 70.40 (3)°. In the crystal, the molecules are linked by intermolecular N-H···O hydrogen bonds into the chains running along the c axis (Fig. 2). The neighboring chains are weakly coupled by π-π stacking interaction between the phenyl ring centroid Cg1 at the position (x,y,z) and the centroid Cg1 at the position (1/2 -x,1/2 -y,-z). The stacking geometry is such that the interplanar distance of the rings is 3.5290 (5) Å, the centroid-centroid distance is 3.7952 (8)Å and the offset is 1.396 (1) Å.

Experimental
Malonic acid (0.3 mol) in dichloromethane (30 ml) was treated with m-toluidine (0.6 mol) in dichloromethane (30 ml), dropwise with stirring. The resulting mixture was stirred for 3 hrs and kept aside for 12 hrs for the completion of reaction and evaporation of the solvent, dichloromethane. The product obtained was added to crushed ice to obtain the precipitate.
The latter was thoroughly washed with water and then with saturated sodium bicarbonate solution and washed again with water. It was then given a wash with 2 N HCl. It was again washed with water, filtered, dried and recrystallized to the constant melting point from ethanol.
Prism like colorless single crystals of the title compound used in X-ray diffraction studies were obtained by a slow evaporation of its ehanolic solution at room temperature.