Molecular structure and intramolecular motion of hexamethyldisiloxane from gas-phase electron diffraction

The molecular structure of hexamethyldisiloxane has been reinvestigated by electron diffraction. The two kinds of large amplitude motion in the molecule, the Si-O-Si bending and the torsion about the Si-O bonds, were treated independently in terms of their potential functions. In the equilibrium structure the molecule has probably C-2v symmetry with staggered C3Si-O-Si fragments and a nonlinear Si-O-Si linkage with an angle of 155 degrees. The barrier to linearization was obtained to be at least 10 kJ mol(-1). In addition, there is free or nearly free internal rotation of the trimethylsilyl groups in hexamethyldisiloxane. In terms of r(g) bond lengths the electron diffraction analysis yielded Si-O 1.639 +/- 0.003 Angstrom, Si-C 1.871 +/- 0.004 Angstrom, and the r(a) angle Si-O-Si 152 +/- 2 degrees. (C) 1997 Elsevier Science B.V.