Question

In the given reactions identify A and B.

• A. A: 2–Pentyne    B: trans–2–butene
• B. A: n–Pentane    B: trans–2–butene
• C. A: 2–Pentyne    B: Cis–2–butene
• D. A: n–Pentane    B: Cis–2–butene

Answer 1

The Correct Option is A

To identify compounds A and B from the given reactions, analyze the transformations:

1. The first reaction is hydrogenation with Pd/C catalyst. Pd/C typically adds hydrogen to alkynes, forming alkenes.
2. Compound A undergoes partial hydrogenation, producing an alkene. Therefore, A must be an alkyne.
3. The product's structure indicates a symmetrical molecule with a trans configuration, specifically trans–2–butene. This trans alkene product suggests the use of a catalyst like Lindlar's catalyst for alkyne hydrogenation.
4. Based on the structure of A, the triple bond must be at the 2-position to yield this product, identifying A as 2–Pentyne.

Thus, for the given reactions, A is 2–Pentyne and B is trans–2–butene, matching option:

• A: 2–Pentyne   B: trans–2–butene