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The reduction of alkynes using sodium in liquid ammonia produces trans-alkenes. What is the name of this reaction?

1. CH3–C≡C–CH3 + H2 → CH3–CH=CH–CH3
2. CH3–C≡C–CH3 + H2 → CH3–CH2–CH2–CH3
3. CH3–C≡C–CH3 + H2 → CH3–CH=CH–CH3 (trans-2-Butene)
4. CH3–C≡C–CH3 + H2 → CH3–CH2–CH2–CH3 (cis-2-Butene)

Correct answer: CH3–C≡C–CH3 + H2 → CH3–CH=CH–CH3 (trans-2-Butene)

Solution

The Birch reduction of alkynes with Na/liq. NH3 selectively produces trans-alkenes. Here, CH3–C≡C–CH3 is reduced to trans-2-Butene (CH3–CH=CH–CH3).

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