AB-INITIO STUDY OF THE INTERNAL-ROTATION POTENTIAL OF P-DISILANYLBENZENE AND P-(1,1',2,2'-TETRAMETHYLDISILANYL)BENZENE

We present a detailed ab initio study of the geometrical structure and torsional potential of p-disiranylbenzene and its methyl derivative p -(1,1',2,2'-tetramethyldisilanyl)benzene. The geometries of the differ ent conformers have been fully optimized at the Hartree-Fock 3-21G an d 6-31G levels. In all cases, the most stable conformation correspond s to the conformer in which the phenylene group lies in a plane perpen dicular to the four silicon atoms. The torsional potential curves calc ulated using the 3-21G and 6-31G* basis sets show similar features. I n the case of p-(1,1',2,2'-tetramethyldisilanyl)benzene the interactio ns between the hydrogen atoms of phenylene and the methyl groups leads to the appearance of a relative minimum when the phenylene group is i n the same plane as that of the silicon atoms.