Which of the following hydrocarbons reacts easily with MeMgBr to give methane?
Which of the following hydrocarbons reacts easily with MeMgBr to give methane?
Show Hint
Alcohols
Terminal alkynes
Highly acidic hydrocarbons (like cyclopentadiene)
Aromatic anion formation increases acidity.
- Option a
- Option b
- Option c
- Option d
The Correct Option is B
Solution and Explanation
\[ \text{MeMgBr} + \text{H–X} \rightarrow \text{CH}_4 \]
Thus, hydrocarbon must contain acidic hydrogen.
Step 1: Identify acidity of options
Cyclopropene: weakly acidic
Cyclopentadiene: highly acidic (pKa \( \sim 16 \))
Benzene: non-acidic
Cyclooctatetraene: non-aromatic, weak acidity
Step 2: Reason
Cyclopentadiene forms aromatic cyclopentadienyl anion after deprotonation (6\(\pi\) electrons), making its hydrogen acidic.
Conclusion:
Cyclopentadiene reacts readily with MeMgBr to produce methane.
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