2,2,2-Tribromo-N-(4-methylphenyl)acetamide

The asymmetric unit of the title compound, C9H8Br3NO, contains two independent molecules which differ in the orientation of the tribromo group. A weak intramolecular N—H⋯Br hydrogen bond is observed in each molecule. In the crystal, the independent molecules are linked into chains along the b axis by intermolecular N—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, C 9 H 8 Br 3 NO, contains two independent molecules which differ in the orientation of the tribromo group. A weak intramolecular N-HÁ Á ÁBr hydrogen bond is observed in each molecule. In the crystal, the independent molecules are linked into chains along the b axis by intermolecular N-HÁ Á ÁO hydrogen bonds.

Comment
As part of a study of the effect of the ring and the side chain substituents on solid state structures of N-aromatic amides (Gowda et al., 2009a,b,c), in the present work, the crytsal structure of 2,2,2-tribromo-N-(4-methylphenyl)acetamide has been determined (Fig.1). The asymmetric unit of the structure contains two independent molecules, which differ in the orientation of the tribromo group as is evident from either the C-N-CO-CBr3 or N-CO-C-Br torsional angles. The conformations of the N-H bonds in both molecules are anti to the C═O bonds in the side chains, similar to those observed in 2,2,2-tribromo-N-(3-methylphenyl)acetamide (Gowda et al., 2009a), 2,2,2-tribromo-N-(phenyl)acetamide (Gowda et al., 2009b), 2,2,2-tribromo-N-(4-chlorophenyl)acetamide (Gowda et al., 2009c) and other amides (Brown, 1966). The structure of the title compound shows both the intramolecular N-H···Br and intermolecular N-H···O hydrogen bonding.

Experimental
The title compound was prepared from p-toluidine, tribromoacetic acid and phosphorylchloride according to the literature method (Gowda et al., 2003). The purity of the compound was checked by determining its melting point. It was further characterized by recording its infrared spectra. Single crystals of the title compound used for X-ray diffraction studies were obtained by a slow evaporation of its solution in petroleum ether at room temperature.

Refinement
H atoms were positioned with idealized geometry using a riding model with C-H = 0.93-0.96 Å, N-H = 0.86 Å and U iso (H) = 1.2U eq (parent atom). The residual electron-density features are located in the region of Br4 and Br3. The highest peak is 0.99 Å from Br4 and the deepest hole is 1.28 Å from Br3. Owing to the poor diffraction quality of the crystal, the R int value is high (0.089) and this is a structure of relatively low precision. Fig. 1. The asymmetric unit of the title compound, showing the atom labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and 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 > 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.