MHTCET 15 May 2024 Shift 2 Paper

Concept:$\mathrm{S_N2}$ is a one-step nucleophilic substitution reaction that proceeds through a single transition state, not through any intermediate.Explanation:In the $\mathrm{S_N2}$ mechanism, the nucleophile attacks the electrophilic carbon from the side opposite to the leaving group.This is known as a backside attack.As the nucleophile approaches, a new bond starts forming while the bond between carbon and the leaving group begins to break.Thus, bond breaking and bond forming happen simultaneously in one concerted step.This makes $\mathrm{S_N2}$ a single-step mechanism.No carbocation intermediate is formed at any stage of the reaction.Only a transition state is formed in which the nucleophile and leaving group are both partially bonded to the carbon atom.The formation of a planar carbocation intermediate is a distinguishing feature of the $\mathrm{S_N1}$ mechanism, where the leaving group departs first to form a stable carbocation.Therefore, the statement about the formation of a planar carbocation intermediate is NOT applicable to the $\mathrm{S_N2}$ mechanism.Answer:Option C: Formation of planar carbocation intermediate.