The structure of the centrosymmetric isomer of 1:2:3:4-tetraphenylcyclobutane

The crystal and molecular structure of the centrosymmetric isomer of l:2:3:4-tetraphenylcyclobutane has been established by a comprehensive X-ray analysis. The intramolecular bond lengths and angles have been determined with an accuracy of about 0.02 A. and 2° respectively. It is found that the benzene rings are regular hexagons of side 1.39 A. and that the bonds adjacent to them are shortened from 1.54 to 1.50 A. An increase from 1.54 A. appears to occur for the bonds in the cyclobutane ring, the measured values being 1.585 and 1.555 A. This increase may be associated with a change in the hybridization ratios of the orbitals in the cyclo butane ring. The molecules are held together by a system of van der Waals bonds between the phenyl groups and achieve a very compact packing in the crystal.