Exams › JEE Advanced › Chemistry
Which of the following compounds undergoes the fastest SN2 reaction with NaI in acetone? (A) CH3Cl, (B) CH3CH2Cl, (C) (CH3)2CHCl, (D) (CH3)3CCl
- CH3Cl (methyl chloride)
- CH3CH2Cl (ethyl chloride)
- (CH3)2CHCl (isopropyl chloride)
- (CH3)3CCl (tert-butyl chloride)
Correct answer: CH3Cl (methyl chloride)
Solution
In SN2 reactions, the nucleophile attacks the carbon from the backside simultaneously as the leaving group departs. Steric hindrance around the electrophilic carbon is the dominant factor. Methyl chloride (CH3Cl) has no alkyl groups on the carbon bearing Cl, so it has the least steric hindrance and reacts fastest. Ethyl chloride (primary) is slower, isopropyl chloride (secondary) is much slower, and tert-butyl chloride (tertiary) essentially does not react by SN2 at all (it prefers E2 or SN1). Order: CH3Cl > CH3CH2Cl > (CH3)2CHCl >> (CH3)3CCl.
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