Why does SN2 favor aprotic?

1 Answer
Bio
Mar 26, 2016

It should be the other way round: aprotic solvent favors "S"_N2.

Explanation:

For "S"_N1, the rate determining step depends on the leaving group. The nucleophile does not play an important role.

For "S"_N2, 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 "S"_N2 reaction occurs as a slower rate.

Hence, "S"_N2 is favored in an aprotic environment, where there is less hindrance to the nucleophiles.

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