Question

For the reaction between alkyl halide and $O{H}^{-}$ increase in solvent polarity generally:

• A. Decreases the rate of $S_{N}1$ reaction
• B. Increases the rate of $S_{N}1$ reaction
• C. Increases the rate of $S_{N}2$ reaction
• D. Does not alter the rate of $S_{N}1$ and $S_{N}2$ reactions

Answer 1

The correct option is B Increases the rate of $S_{N}1$ reaction

A polar solvent would favour and increase the probability of formation of a charged species i.e the cation. Thus, a polar solvent favours $S_{N}1$ reaction by increasing stability of the cation.

Increasing the polarity of the solvent increases the solvation of the nucleophile. There will be increased dipole-dipole interactions between a solvent and a nucleophile as polarity of the solvent increase. This will reduce the mobility of the nucleophile and in turn reduce the rate of reaction in an $S_{N}2$ reaction.