| Popis: |
Low-energy conformations of n-Si4Et10 (1) and a few simpler models (2–8) have been examined by geometry optimization at the HF/6-31G∗ level, and MP2/6-31G∗ single-point energies have been obtained. Five clans of favored backbone conformations of 1, with SiSiSiSi dihedral angles of ∼±40° (C±, cisoid), ∼±60° (G±, gauche), ∼±90° (O±, ortho), ∼±145° (D±, deviant), and ∼±165° (T±, transoid), have been identified. Each contains numerous families characterized by terminal group Et3Si conformations, with ag+g+ and ag+g− particularly advantageous. Each family contains a large number of conformers differing by internal Et2Si conformations, with g±g±/g±g± and ag±/ag± usually energetically the lowest. A simple rationalization is provided for the existence of the C± and D± conformations which do not occur in the permethylated oligosilanes, and implications for the conformational analysis of peralkylated polysilanes are noted. |
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