Symmetrically substituted silanes: (XH 2C) 2SiH 2, (XH 2C) 2SiX 2, (X 2HC) 2SiH 2 and (X 2HC) 2SiX 2 with X = F, Cl or Br. Conformational energies, structures and torsional force constants obtained by molecular-mechanics calculations

Abstract

A series of twelve symmetrically halogen-substituted silanes (XH 2C SiY 2 CH 2X and and X 2HC SiY 2 CHX 2, with Y = H or X, and X = F, Cl or Br) have been investigated using molecular-mechanics calculations, with bonding parameters and interaction potentials derived from earlier gas-phase studies on halogenated alkanes. For the molecules FH 2C SiH 2 CH 2F and FH 2C SiF 2 CH 2F the low-energy conformers are GG and GG″, while for the molecules F 2HC SiH 2 CHF 2 and F 2HC SiF 2 CHF 2 only AA is a low-energy form. The low-energy form of the molecules (X = Cl or Br) XH 2C SiH 2 CH 2X and XH 2C SiX 2 CH 2X is GG. For Cl 2HC SiH 2 CHCL 2 low-energy forms are AG and GG, while for Cl 2HC SiCl 2 CHCl 2 low-energy forms are AA, AG and GG. Only GG is a low-energy conformer in Br 2HC SiBr 2 CHBr 2. The confomers AA, AG, GG and GG″ have staggered terminal groups relative to the central group. However, in Br 2HC SiH 2 CHBr 2 one of the low-energy forms found is AS, possessing one eclipsed terminal group, while the other low-energy form is GG.