Question

Does the solvent play a role in determining which pathway the reaction will take, SN1 versus SN2? How?

Answer 1

It affects more their reaction rates.

Explanation:

The solvents plays a minimal role in determining the mechanism as `S_(N1) or S_(N2)`.

`S_(N1)` mechanism favours polar protic solvents however, `S_(N2)` mechanism favours polar aprotic solvents.

Polar protic solvents can hydrogen bond (or form a strong intermolecular ion-dipole interaction) with the nucleophile and therefore, weakening its nucleophilicity, however, polar aprotic solvents do not interact with the nucleophile.

This is because, `S_(N1)` mechanism favours weak nucleophile and `S_(N2)` mechanism favours strong nucleophile.

Here is a video that explains in details how to predict the mechanism as `S_(N1) or S_(N2)`.