Question

Explain, why SN2 mechanism favours attack of nucleophile from back side and not from front side.

Answer 1

Dear Student,
In SN² both the reacting molecules participate in the rate determining step, the incoming nucleophile attack the atom when leaving group is still attached to it, thus there is steric hindrance on fron side. To avoid this hindrance, nucleophile attacks from back side as it is more favourable situation for reaction which requires lesser energy.

Regards
Rashmi Sheokand