Question
Which of the following is a correct feature of the SN ^2 mechanism?
MHT CET
Chemistry
Haloalkanes and Haloarenes
2026
MHT CET 2026 (15 April Shift 2)
MHT CET Chemistry Question (2026) — Solution
Options
- A. The SN ^2 mechanism proceeds mainly with racemization.
- B. The SN ^2 mechanism includes a transition state with penta coordinating carbon.
- C. The SN ^2 mechanism involves formation of planar carbocation intermediate in the first step.
- D. The SN ^2 mechanism involves formation of carbocation with SP ^2 hybridized carbon.
Answer
B. The SN ^2 mechanism includes a transition state with penta coordinating carbon.
Step-by-step solution
The S _ N 2 mechanism is a concerted, single-step process where the nucleophile attacks the electrophilic carbon from the side opposite to the leaving group. During this process, a transition state is formed in which the central carbon atom is partially bonded to five groups (the incoming nucleophile, the leaving group, and three other substituents), making it penta-coordinated. There is no carbocation intermediate formed in the S _ N 2 mechanism, which rules out the formation of a planar sp ^2 hybridized carbocation. The reaction proceeds with complete inversion of configuration (Walden inversion), not racemization. Answer: The SN ^2 mechanism includes a transition state with penta coordinating carbon.
Related: Chemistry — Haloalkanes and Haloarenes · All PYQ Banks