Consider the internal alkyne 2-pentyne. When subjected to Birch reduction ( ), it forms Product P. W — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

Birch reduction of an internal alkyne proceeds via a single-electron transfer mechanism that involves a radical anion intermediate. Repulsion mandates anti-addition of hydrogen atoms, stereospecifically yielding a $trans$ -alkene ( $trans$ -2-pentene). Reduction with Lindlar's catalyst occurs entirely on the surface of the poisoned metal, forcing syn-addition of hydrogen gas and stereospecifically yielding a $cis$ -alkene ( $cis$ -2-pentene).