Consider the reaction: CH3CH2CH2Br + NaCN → CH3CH2CH2CN + NaBr.This SN2 reaction will be the fastest

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Question

Consider the reaction: CH3CH2CH2Br + NaCN → CH3CH2CH2CN + NaBr.This SN2 reaction will be the fastest in:

Accepted Answer

Correct Answer: A — N,N-Dimethylformamide (DMF)Step-by-step Solution:This is a classic SN2 reaction. The rate depends on the nucleophilicity of CN-.In polar protic solvents (water, ethanol, methanol): The solvent forms hydrogen bonds with the nucleophile (CN-), surrounding it with a solvation shell. This reduces the nucleophile's ability to attack the electrophilic carbon. Rate is slower.In polar aprotic solvents (DMF, DMSO, acetone, acetonitrile): These solvents have a dipole but cannot donate H-bonds. They solvate the cation (Na+) well but leave the anion (CN-) relatively free and unsolvated, making it a much better nucleophile. Rate is faster.Why other options are incorrect:Water, ethanol, and methanol are polar protic solvents. They all hydrogen-bond with CN-, reducing its nucleophilicity and hence the rate of SN2 reaction significantly compared to DMF.Key Concept: SN2 reactions are faster in polar aprotic solvents (DMF, DMSO, CH3CN, acetone) because the nucleophile remains unsolvated and highly reactive. In polar protic solvents, H-bonding solvation of the nucleophile reduces its reactivity. SN1 reactions are favoured by polar protic solvents as they stabilise the carbocation intermediate.

Consider the reaction: CH3CH2CH2Br + NaCN → CH3CH2CH2CN + NaBr.This SN2 reaction will be the fastest in:

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Consider the reaction: CH3CH2CH2Br + NaCN → CH3CH2CH2CN + NaBr.This SN2 reaction will be the fastest in:

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