An unknown alkyne '' reacts with ammoniacal cuprous chloride () solution to form a distinct red prec — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Ammoniacal cuprous chloride ($Cu_2Cl_2 + NH_4OH$) is used as a test for terminal alkynes. The $sp$ -hybridized carbon has an acidic proton that is replaced by copper to form a red copper acetylide precipitate. Internal alkynes (like But-2-yne, Pent-2-yne, Hex-3-yne) lack an acidic terminal hydrogen and do not react. Propyne is a terminal alkyne.