Stereochemistry of 3-isopropoxy-3-methyl-1,3-oxasilinane-the first 3-silatetrahydropyran with an exo-cyclic RO-Si bond

Molecular structure and conformational behavior of 3-isopropoxy-3-methyl-3-oxasilinane is studied by low temperature 13C NMR spectroscopy and theoretical calculations (DFT, MP2). Two conformers, 1-ROax and 1-ROeq, were found experimentally and located on the potential energy surface. LT 13C NMR spectroscopy gives almost equal population of the two conformers at 98 K with ΔG°98K=0.02 kcal/mol in favor of 1-ROax and ΔG#98K=4.5 kcal/mol. The corresponding DFT calculated values (ΔG°98K=0.03 kcal/mol, ΔG#98K=5.1 kcal/mol) are in excellent agreement with the experiment. Detailed DFT and MP2 calculations of the solvent effect on the conformational equilibrium were performed and highlighted the leveling out of the two conformers when transferred from gas to solution.