Question:
Rate determining step in the following reactions I and II respectively is
Rate determining step in the following reactions I and II respectively is
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Electron withdrawing groups like \(-NO_2\) increase rate of SNAr by stabilizing intermediate.
Updated On: Jun 15, 2026
- Cleavage of C-Cl bond in both I and II
- Cleavage of C-Cl bond in I, attack of OH in II
- Attack of OH in I, C-Cl bond cleavage in II
- Attack of OH in both I and II
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The Correct Option is C
Solution and Explanation
Concept:
Aromatic nucleophilic substitution (SNAr) proceeds via addition-elimination mechanism. Electron withdrawing groups stabilize intermediate and affect rate determining step.
Step 1: Reaction I (chlorobenzene). Chlorobenzene is not activated. Reaction proceeds very slowly via formation of Meisenheimer intermediate. Rate determining step: \[ Attack\;of\;OH^- \]
Step 2: Reaction II (p-nitrochlorobenzene). Nitro group strongly stabilizes intermediate. Thus nucleophilic attack becomes fast. Rate determining step shifts to: \[ C-Cl\;bond\;cleavage \]
Step 3: Final conclusion. \[ I:\;Attack\;of\;OH^- \] \[ II:\;C-Cl\;bond\;cleavage \] Hence correct answer: \[ \boxed{C} \]
Step 1: Reaction I (chlorobenzene). Chlorobenzene is not activated. Reaction proceeds very slowly via formation of Meisenheimer intermediate. Rate determining step: \[ Attack\;of\;OH^- \]
Step 2: Reaction II (p-nitrochlorobenzene). Nitro group strongly stabilizes intermediate. Thus nucleophilic attack becomes fast. Rate determining step shifts to: \[ C-Cl\;bond\;cleavage \]
Step 3: Final conclusion. \[ I:\;Attack\;of\;OH^- \] \[ II:\;C-Cl\;bond\;cleavage \] Hence correct answer: \[ \boxed{C} \]
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