The crystal and molecular structure of benzamide

The crystal structure of a stable form of benzamide has been determined by means of electrondensity projections down the two short crystallographic axes. The crystals are monoclinic, space group P2~/c with a ----5.59, b = 5.01, c ----21.93 A, fl = 90 45'. Measurements of bond lengths and angles, with standard deviations of 0.017 A and 1-0 respectively, have enabled estimates to be made of bond orders in the amide group in which C-N ---1.31, C-O = 1.24 A. The molecules are non-planar with an angle of 26 between the amide group and benzene ring. The non-planarity is shown to be due to steric hindrance and is discussed in relation to similar molecules of known configuration. Hydrogen bonds connect pairs of molecules into centrosymmetrical dimers which are themselves linked by further hydrogen bonds into endless chains.