Please give your own answer not just the answer from the mar

(c) Suggest why polar, aprotic solvents are more suitable for S,2 reactions whereas polar, protic solvents favour S, I reactions. S 2:

Solution

S_N2:

In S_N2_, the solvent is polar aprotic. Polar aprotic solvents do not contain positively polarized or charged hydrogen atom. In S_N2, the nucleophile is anionic and involved in the rate determining step of the reaction. A polar protic solvent interacts with the anionic nucleophile via the positively polarized hydrogen atom and hence, reduces the nucleophilicity of the nucleophile. Since the nucleophile is involved in the rate limiting step of the S_N2 reaction, hence, the rate of the reaction falls. Therefore, S_N2 reactions are favored by polar aprotic solvents. Polar aprotic solvents stabilize the transition state in S_N2 reactions without affecting the rate of the reaction.

S_N1:

In S_N1 reaction, the intermediate is a carbocation while the nucleophile is a neutral molecule. The rate-determining step of a S_N1 reaction is unimolecular and only the reactant (alkyl halide or alcohol) is involved in the rate limiting step of the reaction. A polar solvent reduces the nucleophilicity of the nucleophile and increases the leaving group character of the leaving group. At the same time, the polar solvent stabilizes the charged carbocation intermediate, thereby, increasing the rate of the S_N1 reaction.