Molecular structure of 3,3-dimethyl-3-silatetrahydrofuran from gas-phase electron diffraction analysis and ab initio calculations

Abstract

The molecular structure of 3,3-dimethyl-3-silatetrahydrofuran has been studied by means of gas-phase electron diffraction (GED) and ab initio calculations at the HF/6-31G∗ level. Six different conformers of the title compound have been refined in the course of the GED analysis, allowing the vibrational amplitudes to vary over a wide range. Several bond length differences were taken from the results of the ab initio geometry refinement. Almost the same value of the R-factor, about 3%, has been obtained for all six models, whereas the ab initio calculation resulted in one single conformer (“O-envelope”). Based upon the combined information from the ab initio calculations and the GED work, the “O-envelope” conformer is chosen as the final structure. Geometrical parameters obtained (GED) are as follows (bond lengths in Ångströms, angles in degrees; three times standard deviation estimates in parentheses): r(SiC cyc) = 1.891(3) and 1.904; r(SiC) Me) = 1.877 and 1.879; r(CC) = 1.556(7); r(CO) = 1.431(3) and 1.445; r(C cycH) = 1.11(2); r(C MeH) = 1.10(2); ф( O C C Si) = 33.0(14) ; ∠C cycSiC cyc = 92.2(5); ∠C MeSiC Me = 107.2(8); ∠SiCC = 102.6(6); ∠CCO = 109.9(11); ∠HC cycH = 110.5(47); ∠SiC MeH = 111.6(14).