Question

The rate of S\(_N\)2 reaction is maximum when the solvent is

• A. CH\(_3\)OH
• B. H\(_2\)O
• C. DMSO
• D. benzene

Hint:

Common polar aprotic solvents: DMSO, DMF, acetone, acetonitrile. They are excellent for S\(_N\)2 reactions.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
S\(_N\)2 reactions are favored by polar aprotic solvents. These solvents solvate the cation but not the anion, leaving the nucleophile highly reactive.
Step 2: Detailed Explanation:
\begin{itemize} \item CH\(_3\)OH and H\(_2\)O are polar protic solvents. They solvate the nucleophile through hydrogen bonding, reducing its nucleophilicity and thus slowing the S\(_N\)2 reaction. \item DMSO (dimethyl sulfoxide) is a polar aprotic solvent. It solvates the cation but not the anion, leaving the nucleophile "naked" and highly reactive, maximizing the S\(_N\)2 rate. \item Benzene is non-polar and does not stabilize the charged transition state, so the reaction is very slow. \end{itemize}
Step 3: Final Answer:
The rate of S\(_N\)2 reaction is maximum in DMSO, option (C).