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

In a SN1 reaction, there is a formation of carbocation after removal of halide from reactant and this step is slow and rate determing step. so, it is necessary to solvate both reactant and nucleophile during the reaction, For that purpose, We need to use polar protic solvent which can solvate carbocation as well as nucleophile. out of acetone, n propanol or water. Acetone is a polar aprotic solvent, it will only solvate carbocation not nucleophile While n propanol or water both are polar protic solvent so they both can be use as a solvent. But generally water is used because of more polar protic solvent than propanol.