A combined ab initio and gas-phase electron diffraction investigation of the molecular structure and conformation of (silylmethyl)cyclopropane

Abstract

The molecular structure and conformational composition of (silylmethyl)cyclopropane (SMCP), C 3H 5CH 2SiH 3, with respect to the C ringCH 2 and the CH 2Si axes have been studied by gas-phase electron diffraction and ab initio calculations using a 6-31G∗ basis set. The conformational analysis, with respect to the C ringC bond, has shown that the gauche (skew) form is the predominant conformation (> 98%) in the gas phase. A reasonable explanation for the preference of the gauche conformation is provided by the σ–π hyperconjugation effect. Repulsive through-space interactions are most probably responsible for the cis conformer, being higher in energy and thus less favorable. The major bond distances (r a, Å −1) and angles (°) for the skew conformer obtained from the least-squares refinements with uncertainties estimated at 3σ are r(CH) = 1.120(4), r(C 1C 2) ring = 1.510(10), r(C 2C 3) ring = 1.490(12), r(C ringC) = 1.540(10), r(SiC) = 1.876(2); ∠HSiC = 111.0(2.0), ∠SiCC = 112.1(1.0), ∠CC(ring plane) = 122.7(0.5), and the dihedral torsional angle τ SiCCX = 119.0(2.0) (X is the center of the ring).