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 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 conformers 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.