MHT CET Chemistry Question (2026) — Solution

Step-by-step solution

The S _ N 1 reaction proceeds via the formation of a carbocation intermediate in its rate-determining step. Bulky alkyl groups on the carbon atom attached to the halogen atom (such as in tertiary alkyl halides) stabilize the resulting carbocation through the +I inductive effect and hyperconjugation. Additionally, the steric crowding in the initial tetrahedral substrate is relieved when it forms a planar carbocation, which provides a driving force for the S _ N 1 mechanism. In contrast, a strong nucleophile and small alkyl groups favor the S _ N 2 mechanism, while non-polar solvents do not favor the ionization step required for S _ N 1. Answer: Bulky alkyl groups on the carbon atom attached to halogen atom