Question:
Identify the major product ‘Q’ in the following reaction:
Identify the major product ‘Q’ in the following reaction:
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Vicinal dibromides with strong base and subsequent hydrolysis give ketones via E2 and hydrolysis of the intermediate.
Updated On: Jul 18, 2026
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The Correct Option is B
Solution and Explanation
Step 1: Analyze first step (KOH in alcohol, heat).
Vicinal dibromide undergoes dehydrohalogenation to form an alkene via elimination reaction (E2 mechanism).
Step 2: Analyze second step (NaNH\(_2\), liquid NH\(_3\), 196 K).
Strong base abstracts protons; in this reaction, alkene undergoes rearrangement if needed to form more stable intermediate.
Step 3: Analyze third step (H\(_2\)SO\(_4\), dilute).
Acidic aqueous work-up leads to hydration of the triple bond or rearranged intermediate, forming a ketone. This is consistent with formation of acetophenone (C\(_6\)H\(_5\)COCH\(_3\)).
Step 4: Rationalize product.
The sequence overall converts the vicinal dibromide to the corresponding methyl ketone via elimination, acetylide formation, and hydrolysis.
Step 5: Check other options.
Benzaldehyde would require terminal oxidation; C\(_6\)H\(_5\)CH\(_2\)Br is starting material; p-bromobenzaldehyde is unrelated. Only acetophenone matches reaction pathway.
Step 6: Final conclusion.
Major product ‘Q’: \[ \boxed{\text{C}_6\text{H}_5\text{COCH}_3 \text{ (Acetophenone)}} \]
Vicinal dibromide undergoes dehydrohalogenation to form an alkene via elimination reaction (E2 mechanism).
Step 2: Analyze second step (NaNH\(_2\), liquid NH\(_3\), 196 K).
Strong base abstracts protons; in this reaction, alkene undergoes rearrangement if needed to form more stable intermediate.
Step 3: Analyze third step (H\(_2\)SO\(_4\), dilute).
Acidic aqueous work-up leads to hydration of the triple bond or rearranged intermediate, forming a ketone. This is consistent with formation of acetophenone (C\(_6\)H\(_5\)COCH\(_3\)).
Step 4: Rationalize product.
The sequence overall converts the vicinal dibromide to the corresponding methyl ketone via elimination, acetylide formation, and hydrolysis.
Step 5: Check other options.
Benzaldehyde would require terminal oxidation; C\(_6\)H\(_5\)CH\(_2\)Br is starting material; p-bromobenzaldehyde is unrelated. Only acetophenone matches reaction pathway.
Step 6: Final conclusion.
Major product ‘Q’: \[ \boxed{\text{C}_6\text{H}_5\text{COCH}_3 \text{ (Acetophenone)}} \]
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