NMR spectroscopic and computational investigations of σ-interactions in carbocations: The β-silyl effect in vinyl cations

Abstract

The para carbon chemical shift in 1-mesityl substituted vinyl cations and the torsional barrier for the methoxy group rotation in 1-p-(anisyl)vinyl cations are used to evaluate the magnitude of the silyl effect. The hyperconjugative stabilization by β-silicon groups and the accompanying geometrical distortions are studied experimentally and computationally in dienyl-cations and 1-cyclopropylvinyl cations. A geminal methyl substituent enhances the interaction of a β-silyl group with the vacant p-orbital. © 1995 IUPAC