Consider the partial stereoselective hydrogenation of 2-butyne. Which of the following statements is — Hydrocarbons Chemistry Question

💡 Solution & Explanation

(A) Lindlar's catalyst causes syn-addition (hydrogen adds from the same face), yielding the *cis*-alkene. (B) Birch reduction ($Na/\text{liq.} NH_3$) causes anti-addition, yielding the *trans*-alkene. (C) is incorrect because Lindlar's catalyst forces syn-addition via a metal-surface mechanism, not anti-addition. (D) is correct; Birch reduction proceeds via successive electron/proton transfers, minimizing electron repulsion in the radical anion intermediate to form the more stable *trans* geometry.