Question

Which one of the following does not give precipitate with ammoniacal cuprous chloride?

• A. $H_{3}C-C{H}_2-C\equiv CH$
• B. $H_{3}C-C\equiv CH$
• C. $HC\equiv CH$
• D. $H_{2}C-C\equiv C-C{H}_3$

Answer 1

The correct option is D $H_{2}C-C\equiv C-C{H}_3$

Terminal alkynes contain acidic hydrogen. These terminal alkynes react with ammoniacal solutions of cuprous chloride to give red precipitate of copper alkynide.
2-butyne is a non-terminal alkyne whereas other compound are terminal alkynes.
Therefore, 2-butyne $H_{3}C-C\equiv C-C{H}_3$ does not give precipitate with ammoniacal cuprous chloride. This reactions is given only by terminal alkynes which has acidic hydrogen atom.