Chemical shift anisotropies in silicon containing three-membered rings. An ab initio study

Ab initio NMR shielding calculations were carried out for cyclic compounds containing the cyclotrisilane, silaoxirane, disilacyclopropane, silacyclopropane, cyclotetrasilane, cyclopentasilane and cyclohexasilane skeletons. Calculations were performed for all permethylated compounds, as well as for the fully tert-butyl substituted cyclotrisilane. Geometries were optimized at the SCF/3–21G(∗) level while NMR shieldings were evaluated using large basis sets. The results reproduce the high 29 Si chemical shift anisotropies observed in three-membered rings. Calculations on strongly distorted models with local geometries similar to those in small rings suggest that the high anisotropy is due to the distorted geometry around the Si atom, not to special bonding effects in the three-membered rings.