# Why does SN2 favor aprotic?

Mar 26, 2016

It should be the other way round: aprotic solvent favors ${\text{S}}_{N} 2$.

#### Explanation:

For ${\text{S}}_{N} 1$, the rate determining step depends on the leaving group. The nucleophile does not play an important role.

For ${\text{S}}_{N} 2$, that is not the case. The more nucleophilic the nucleophile, the faster the reaction.

In protic solvents, the nucleophile is "trapped" in a cage of solvent molecules, and becomes less nucleophilic. Consequently, the ${\text{S}}_{N} 2$ reaction occurs as a slower rate.

Hence, ${\text{S}}_{N} 2$ is favored in an aprotic environment, where there is less hindrance to the nucleophiles.