Which reagent is most suitable for the conversion of an alkyne to a trans-alkene?

B. Na/NH_3(l) — Birch reduction using sodium in liquid ammonia stereoselectively produces trans-alkenes from internal alkynes.

JEE Main · ChemistryHard

$Which reagent is most suitable for the conversion of R-C \equiv C-R to a trans-alkene?$

Show correct answer & step-by-step solution

Correct answer: B — $Na/NH_{3} (l)$

$Reduction of internal alkynes to trans-alkenes requires a dissolving metal reduction.$
$Sodium in liquid ammonia provides solvated electrons to the alkyne.$
$The mechanism involves a radical anion intermediate that adopts a trans configuration to minimize steric repulsion.$
$Protonation of the intermediate yields the trans-alkene.$
$Hence the answer is (B).$