An ab initio study of the effect on the Si-29 NMR chemical shift of dihydroxysilane of geometry changes expected on approach to a surface

Si-29 nuclear magnetic resonance spectroscopy has shown that when dialkoxysilanes are milled with magnesium chloride. a component of the Ziegler-Natta catalyst, the Si-29 nucleus becomes more deshielded. Calculations on the change in Si-29 NMR shielding when the Si-O bond distances and O-Si-O bond angle vary are reported for the model compound silanediol. The results indicate that changes in geometry do not produce a sufficiently large change in Si-29 NMR shielding and the conclusion is drawn that the deshielding is due to interaction of the dialkoxysilanes with the magnesium chloride surface.