Question:
Identify the product when but-2-yne is treated with \(\text{H}_{2}\) gas in the presence of Lindlar's catalyst.
Identify the product when but-2-yne is treated with \(\text{H}_{2}\) gas in the presence of Lindlar's catalyst.
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Lindlar's catalyst gives syn addition of hydrogen, which yields the cis alkene.
Updated On: Nov 12, 2026
- Cis-But-2-ene
- Trans-But-2-ene
- Mixture of both
- Butane
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept
Lindlar's catalyst is palladium on \(\text{CaCO}_3\) poisoned with quinoline or lead acetate. It stops hydrogenation at the alkene stage.
Step 2: Stereochemistry
Both hydrogen atoms add to the same side of the triple bond, which is syn addition.
\(\text{CH}_3\text{-C}\equiv\text{C-CH}_3 + \text{H}_2 \rightarrow \text{cis-CH}_3\text{CH=CHCH}_3\)
Step 3: Compare the options
The product is cis-but-2-ene, option (A).
Final Answer:
The product is cis-but-2-ene. \[ \boxed{\text{(A) }\text{Cis-But-2-ene}} \]
Lindlar's catalyst is palladium on \(\text{CaCO}_3\) poisoned with quinoline or lead acetate. It stops hydrogenation at the alkene stage.
Step 2: Stereochemistry
Both hydrogen atoms add to the same side of the triple bond, which is syn addition.
\(\text{CH}_3\text{-C}\equiv\text{C-CH}_3 + \text{H}_2 \rightarrow \text{cis-CH}_3\text{CH=CHCH}_3\)
Step 3: Compare the options
The product is cis-but-2-ene, option (A).
Final Answer:
The product is cis-but-2-ene. \[ \boxed{\text{(A) }\text{Cis-But-2-ene}} \]
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