Question

1. Why does an SN2 reactions prefer polar aprotic solvents?

2. Why does SN1/E1 prefer polar protic solvents?

please explain....

Answer 1

1.

SN2 reaction is concerted mechanism means transition state is the intermediate

transition state required polar solvent

at the same time nucleophile used is strong nucleophile it doesnt require polar protic

if you use the polar protic it forms hydrogen bonding with nucleophile it decreases the nucleophilicity of the nucleophile

so transition state required polar solvent and nucleophile doesnt required polar protic so

with this two qualities we will get with polar aprotic

2.

SN1 or E1 mechanism is ionic mechanism

here carbo cation is intermediate

here first step is dissociation step

if you use the polar protic solvent in this positive part od the solvent coordinate with leaving group

and -ve part of the solvent stabilises the cation

means which helps to dissociate quickly

so polar protic solvent is require to dissociation step

that why this is favoured in SN1 and E1 mechanism