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

Abstract 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 C 3 Si–O–Si fragments and a nonlinear Si–O–Si linkage with an angle of 155°. 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 A, Si–C 1.871±0.004 A, and the r a angle Si–O–Si 152±2°.