Question

Which of the following reagents result in syn-addition of hydrogen atoms to a triple bond?

• A. Lindlar Catalyst
• B. $Na/liq.N{H}_3$
• C. Baeyer's reagent
• D. None of the above

Answer 1

The correct option is A Lindlar Catalyst

$\text{Lindlar catalyst}\to H_2/Pd(CaC{O}_3,Quinoline)$
Here, the alkyne will undergo partial reduction to form cis-alkene. Both the $H$ atom gets add to the alkyne in same direction to give cis- product.

Reduction of alkyne using $Na/liq.N{H}_3$ is called Birch reduction. In this $H$ gets add to the triple bond in opposite direction to give trans product.

$\text{Baeyer's reagent}\to \text{Alkaline cold}dil.KMn{O}_4$. This reagent oxides the alkene reactant by syn addition of $OH$.
It reacts with ethene to form Ethane-1,2-diol (glycol).