text: The carbon-silicon bond is highly electron-releasing and can stabilize a positive charge in the β position through hyperconjugation. Electrophilic additions to allyl- and vinylsilanes take advantage of this, and site selectivity generally reflects this property—electrophiles become bound to the carbon γ to the silyl group. The electron-donating strength of the carbon-silicon bond is similar to that of an acetamide substituent and equal to roughly two alkyl groups. After formation of the carbon-electrophile bond, silicon elimination is assisted by a nucleophile.
  A model of the most likely reactive conformation of the allylsilane (see below) suggests that the new double bond that forms will predominantly possess the (E) configuration. However, addition of a nucleophile (such as the counterion of the electrophile) to the intermediate silyl-stabilized carbocation complicates this picture. Because the elimination to generate the double bond is stereospecifically anti, nucleophilic addition to either face of the silyl-stabilized carbanion leads to the formation of mixtures of double bond isomers. Diastereomeric mixtures of double bond isomers are common when Lewis acids are used to activate the electrophile.
  Under conditions of nucleophilic catalysis, any intermediate along the reaction pathway may incorporate a silicon-nucleophile bond. This factor does not affect the outcome unless nucleophilic attack liberates free anions or allylic transposition occurs. The latter is known to occur for hypervalent allylsilanes incorporating fluoride.