Question

If the separation of halide ion from carbon is the rate-determining step in the SN1 reaction, one would want a solvent which stabilizes the resulting cation and anion to speed up the reaction. Which solvent would you choose for this role, acetone, n-propanol, or water? Presume the alkyl halide is soluble in all three possible solvents.

Answer 1

For Sn1 reaction, rate of reaction will depends on solvolysis of alkyl halide to produce carbocation and halide ion. Solvolysis of alkyl halide dictated by the solvent used for the reaction.

Polar protic solvent generally increasses the rate of formation and stability of carbocation and halide ion. Out of the listed solvent (acetone, n-propanol and water) water has highest dielectric constant and can increases the relative rate of reaction.

So, water is the best solvent for SN1 reaction.