Question

Which of the follwing is correct ? Please solve it

Answer 1

The answer is (4)

Explanation:

`H_2`/`Pd -BaSO_4` is a set of reagents called Lindlar's catalyst. Lindlar's catalyst is used for controlled hydrogenation of alkynes to give cis-alkenes. Hydrogenation using Lindlar's catalyst follows syn-addition.

`Na`/`NH_3` is a reagent for birch reduction which is also used for controlled hydrogenation of alkynes, but this reagent gives trans-alkene. Hydrogenation by Birch Reduction follows anti-addition.

When one equivalent of Lindar's catalyst is given to the molecule, syn-addition takes place. We can choose anyone of the alkyne group as they are present symmetrically. Syn-Addition of hydrogen results in one of the alkyne group to get converted into cis-alkene.

Now, Birch reduction occurs at the other alkyne group, thus converting it into a trans alkene.

The alkene group present in the middle is already trans, so we have, the first alkyne converted into cis-alkene, the already present trans alkene group stays intact, and the last alkyne group becomes trans-alkene. The only option that fits our description is (4)