Benzyne Mechanism
Hardchemistry
Elimination-addition (benzyne) mechanism is favored by treatment of chlorobenzene with:
Select the correct option:
Solution
Incorrect! Answer:
Molten NaOH (fused) or strong base at high temp
- Dow's Process Mechanism: Chlorobenzene does not undergo nucleophilic substitution under normal conditions due to partial double bond character.
- Extreme Conditions: Under high pressure and temperature (623K and 300 atm) with NaOH, reaction occurs.
- Benzyne Formation: A very strong base (OH− or NH2−) abstracts an ortho-hydrogen, following which the halide leaves, creating a triple bond within the benzene ring (Benzyne intermediate).
- Attack: The nucleophile then attacks the benzyne to restore the aromatic system.
- Requirement: This pathway requires high energy (molten/fused alkali) to overcome the aromatic stability barrier.
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About This Question
- Subject
- chemistry
- Chapter
- halogen organics
- Topic
- benzyne mechanism
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
Molten NaOH (fused) or strong base at high temp
- Dow's Process Mechanism: Chlorobenzene does not undergo nucleophilic substitution under normal conditions due to partial double bond character.
- Extreme Conditions: Under high pressure and temperature (623K and 300 atm) with NaOH, reaction occurs.
- Benzyne Formation: A very strong base (OH− or NH2−) abstracts an ortho-hydrogen, following which the halide leaves, creating a triple bond within the benzene ring (Benzyne intermediate).
- Attack: The nucleophile then attacks the benzyne to restore the aromatic system.
- Requirement: This pathway requires high energy (molten/fused alkali) to overcome the aromatic stability barrier.
This hard difficulty chemistry question is from the chapter halogen organics, covering the topic of benzyne mechanism. It appeared in the 2025 exam.
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