Which of the following statements is/are correct regarding nucleophilic substitution reactions of alkyl halides?
A. In case of optically active alkyl halides, the substitution product obtained as a result of SN2 mechanism has inverted configuration.
B. SN1 mechanism involves a transition state.
C. SN2 mechanism is a two-step process involving the formation of an intermediate.
D. In case of optically active alkyl halides, the substitution product obtained as a result of SN1 mechanism is a racemic mixture.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A and D only
Note: The given answer is as per the official NTA Answer Key. However, the correct answer should be Option (1) A, B and D only, as explained below.
SN2: one step through a single transition state, with no intermediate. The nucleophile attacks from the back, so the configuration is inverted.
SN1: two steps through a carbocation intermediate. Each step has its own transition state. The planar carbocation is attacked from both sides, which gives a racemic mixture.
(A) In case of optically active alkyl halides, the substitution product obtained as a result of SN2 mechanism has inverted configuration. — Correct. Backside attack inverts the configuration.
(B) SN1 mechanism involves a transition state. — Correct as per NCERT. SN1 passes through two transition states, one for each step.
(C) SN2 mechanism is a two-step process involving the formation of an intermediate. — Incorrect. SN2 is one step with no intermediate.
(D) In case of optically active alkyl halides, the substitution product obtained as a result of SN1 mechanism is a racemic mixture. — Correct. Attack from both faces of the carbocation gives racemisation.
Option (4) A and D only — The answer given by NTA, but incorrect. It leaves out statement B, which is correct; A, B and D together are Option (1).