Question

The reagent that is used to convert but-2-yne to trans-but-2-ene is

• A. \(Na/liquid NH_3\)
• B. \(NaBH_4\)
• C. Sn/HCI
• D. \(H_2/Pd/C\)
• E. Zn-Hg/HCl

Answer 1

The Correct Option is A

To convert but-2-yne to trans-but-2-ene, we need to reduce the triple bond in but-2-yne (an alkyne) to a double bond in trans-but-2-ene (an alkene). This requires a specific reagent that induces partial hydrogenation and selectively gives the trans isomer.

The reagent used to achieve this transformation is sodium in liquid ammonia (Na/liquid NH₃). This reagent reduces alkynes to trans-alkenes via an anti-addition mechanism.

• H₂/Pd/C: Reduces the alkyne to cis-but-2-ene (syn addition), not the trans isomer.
• NaBH₄: A mild reducing agent, not suitable for reducing alkynes to alkenes.
• Sn/HCl: Typically used for reducing nitro groups, not alkynes.
• Na/liquid NH₃: Selectively reduces alkynes to trans-alkenes.

Correct Answer:

Correct Answer: (A) Na/liquid NH₃