Question

What is the effect of leaving group and solvent on the reaction rate of `S_N2` reaction?

Answer 1

Greater rate: Better leaving group & polar aprotic solvent .

Explanation:

`S_(N2)` is a bimolecular molecule and the reaction rate depends on the alkyl halide and the nucleophile.

`S_(N2)` has a concerted mechanism which means that it occurs in one step which is itself the rate determining step:

`R=k[R-X][Nu^-]`

Effect of leaving group:
The better the leaving group the faster the reaction and therefore greater reaction rate.

Effect of solvent:
`S_(N2)` favours polar aprotic solvents.
Polar aprotic solvents do not affect the strength of the nucleophile (`S_(N2)` favours strong nucleophiles), therefore, the reaction will proceed at a faster rate.