Substitution

Question 1

How does a polar, aprotic solvent affect an Sn2 reaction?

Answer 1

Increases the rate of reaction
The solvent is not polar enough, or protic, to be able to solvate the nucleophilic anion
The solvent can solvate the TS as less polar, charge spread over multiple atoms
And so this enables greater nucleophilic substitution

Question 2

How does a polar, protic solvent affect an Sn2 reaction?

Answer 2

The protic solvent can stabilise the carbocation intermediate, more greatly than the nucleophile, as the nucleophile is likely uncharged
It can also solvate and stabilise the transition state