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NEET CHEMISTRYAlcohols, Phenols and EthersMedium

Question

Consider the reaction: CH3CH2CH2Br+NaCN→CH3CH2CH2CN+NaBr\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + \text{NaCN} \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{CN} + \text{NaBr} This reaction will be the fastest in

A

ethanol

B

methanol

C

N,N'-dimethylformamide (DMF)

D

water

Step-by-Step Solution

The given reaction is an SN2S_N2 nucleophilic substitution reaction, as it involves a primary alkyl halide (1-bromopropane) reacting with a strong nucleophile (CN−\text{CN}^-). SN2S_N2 reactions proceed fastest in polar aprotic solvents. These solvents effectively solvate cations (like Na+\text{Na}^+) but do not strongly solvate anions (like CN−\text{CN}^-) via hydrogen bonding, leaving the nucleophile highly reactive. Among the given options, water, methanol, and ethanol are polar protic solvents. N,N'-dimethylformamide (DMF) is a polar aprotic solvent, making it the ideal choice to accelerate this SN2S_N2 reaction.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Alcohols, Phenols and Ethers. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

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