2-Methyl-N-p-tolylbenzamide: a second monoclinic polymorph

The title compound, C15H15NO, (I), is a polymorph of the structure (II) reported by Gowda et al. [Acta Cryst. (2008), E64, o1494]. Compound (II) crystalllizes in the space group C2/c (Z = 8), whereas the title compound occurs in space group P21/c (Z = 4). The two molecular structures differ slightly in the relative orientations of their central amide group with respect to the benzoyl ring [dihedral angles of 55.99 (7) for (I) and 59.96 (11)° for (II)] and in the inclination of the benzoyl and aniline rings [88.67 (8) for (I) and 81.44 (5)° for (II)]. In the crystal structure of (I), molecules are linked by N—H⋯O hydrogen bonds, forming C(4) chains, which are augmented by weak C—H⋯O interactions. The structure is further stabilized by C—H⋯π contacts involving both of the aromatic rings.

The title compound, C 15 H 15 NO, (I), is a polymorph of the structure (II) reported by Gowda et al. [Acta Cryst. (2008), E64, o1494]. Compound (II) crystalllizes in the space group C2/c (Z = 8), whereas the title compound occurs in space group P2 1 /c (Z = 4). The two molecular structures differ slightly in the relative orientations of their central amide group with respect to the benzoyl ring [dihedral angles of 55.99 (7) for (I) and 59.96 (11) for (II)] and in the inclination of the benzoyl and aniline rings [88.67 (8) for (I) and 81.44 (5) for (II)]. In the crystal structure of (I), molecules are linked by N-HÁ Á ÁO hydrogen bonds, forming C(4) chains, which are augmented by weak C-HÁ Á ÁO interactions. The structure is further stabilized by C-HÁ Á Á contacts involving both of the aromatic rings.
The title compound, (I), is a second monoclinic polymorph of the structure of this benzamide derivative which crystallises in the space group P21/c. An alternative structure, II, in the space group C2/c was reported previously by Gowda et al., (2008). The major structural differences between the two polymorphs lie in the orientations of their central C2,C1,O1,N1,C8 amide groups with respect to the C2···C6 benzoyl ring. In I the N1-C1-C2-C7 dihedral angle is 55.69 (3) for (I) whereas for (II) it is -60.69 (18). Furthermore the angle between the plane through C2,C1,O1,N1,C8 and the C2···C6 ring plane is 55.99 (7)/% in (I) but 59.96 (11) for (II) and the two phenyl rings are respectively inclined at 88.67 (8)/% for (I) and 81.44 (5)/% for (II). Bond distances in the molecule are normal and comparable to those in the second polymorph and in a closely related benzamide derivative (Gowda et al., 2009).
Experimental 2-Methylbenzoyl chloride (1 mmol) in CHCl 3 was treated with 4-methylaniline (3.5 mmol) under a nitrogen atmosphere at reflux for 3.5 h. Upon cooling, the reaction mixture was diluted with CHCl 3 and washed consecutively with 1 M aq HCl and saturated aq NaHCO 3 . The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure.

Refinement
The H atom bound to N1 was located in a difference map and refined isotropically. All other H-atoms were positioned geometrically and refined using a riding model with d(C-H) = 0.95 Å, U iso = 1.2U eq (C) for aromatic and d(C-H) = 0.98 Å, U iso = 1.5U eq (C) for methyl C atoms. Crystals were very thin and weakly diffracting. Even with 60 s scans over 24 h, no useful data was observed beyond theta = 20.71 °.  Fig. 1. The structure of (I) with displacement ellipsoids for the non-hydrogen atoms drawn at the 50% probability level.

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 > 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.