N-(3-Bromophenyl)-3,4,5-trimethoxybenzamide

In the title compound, C16H16BrNO4, the dihedral between the planes of the aromatic rings is 7.74 (18)°. The amide group is tilted with respect to the bromo- and methoxy-substituted aromatic rings by 36.3 (8) and 35.2 (8)°, respectively. The meta-methoxy groups are essentially in-plane with the aromatic ring [dihedral angles CH3—O—C—C = −4.6 (4) and −2.5 (4)°]. The para-methoxy group is markedly displaced from the ring plane [dihedral angle CH3—O—C—C = −72.5 (4)°]. The crystal packing is stabilized by N—H⋯O hydrogen bonds linking the molecules into chains running along the b axis.


Comment
The background to this study has been described in an earlier paper on N-(2-chlorophenyl)-4-chlorobenzamide (Saeed et al., 2009). As part of our work on the structure of benzanilides and related compounds, we report here the structure of the This can be attributed to a combination of resonance effects, which lead for aromatic methoxy groups to being coplanar with an aromatic ring, and steric interactions, which prohibit a coplanar arrangement when more than two methoxy groups are present per benzene moiety (Vande Velde et al., 2006). The crystal packing is stabilized by N-H···O hydrogen bonds linking the molecules to chains running along the b axis (Fig. 2).
Experimental 3,4,5-Trimethoxybenzoyl chloride (5.4 mmol) in CHCl 3 was treated with 3-bromoaniline (21.6 mmol) under a nitrogen atmosphere at reflux for 3 h. Upon cooling, the reaction mixture was diluted with CHCl 3 and washed consecutively with aq 1 M HCl and saturated aq NaHCO 3 . The organic layer was dried over anhydrous magnesium sulfate and concentrated under reduced pressure. Crystallization of the residue in CHCl 3 afforded the title compound (81%) as colourless needles.
Anal. calcd. for C 16 H 16 BrNO 4 : C, 52.48; H, 4.40; N, 3.82%; found: C, 52.51; H, 4.36; N, 3.87 Refinement H atoms were located in a difference map but those bonded to C were geometrically positioned and refined using a riding model with fixed individual displacement parameters [U(H iso ) = 1.2U eq (C) or U(H iso ) = 1.5U eq (C methyl )] using a riding model with C aromatic -H = 0.95 Å or C methyl -H = 0.98 Å. The H atom bonded to N was freely refined.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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.