X-ray analysis of the crystal structure of durene

The crystal structure of durene, 1. 2. 4. 5. (sym.)-tetramethyi benzene, C6H2(CH3)4, has not previously been examined by the X-ray method, but the class and axial ratios are given by Groth as monoclinic prismatic a:b:c = 2·4609:1:1·9975, β = 115°27' with the (100) face most prominently developed. The present work confirms these measurements to within the limits of experimental error (about ½%), but it is found that the axial directions used above define a cell which contains an identical molecule at the centre of the ac face. It is therefore necessary to select a new axis in order to define the true unit cell. The relation of Groth’s axial directions to the cell now chosen is illustrated in fig. 1, the b axis being perpendicular to the paper. The X-ray work, recorded by means of rotation, oscillation, and moving film photographs, leads to the following values for the axial lengths, etc.:— a = 11·57 ± 0·05 A. b = 5·77 ± 0·02 A. c = 7·03 ± 0·05 A. β = 113·3° {h01} halved when h is odd, (010) halved.