JEE Main · 2018 · 08 Apr 2018 · Offline · Hydrocarbons

The trans-alkenes are formed by the reduction of alkynes with :

(A) $Sn - HCl$
(B) $H_{2} - Pd / C, BaSO_{4}$
(C) $NaBH_{4}$
(D) $Na$ /liq. $NH_{3}$ ✓ Correct

Answer: (D)

Solution

Dissolving-metal reduction with sodium in liquid ammonia delivers the two hydrogens to the triple bond from opposite faces through a trans vinyl radical anion, so the alkyne is converted to the trans-alkene; hydrogen over a poisoned palladium catalyst would instead give the cis product. The reagent that yields trans-alkenes is

Na

in liquid

NH X_{3}

JEE Main · 2018 · 08 Apr 2018 · Offline · Single correct option

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