Question

Identify the alkyne in the following sequence of reactions,
Alkyne $ \xrightarrow[{\text { Lindlar's catalyst }}]{ H _{2}} A \xrightarrow{\text { Ozonolysis }} \underset {\text{ only }}{B} \xleftarrow[{\text { process }}]{\text { Wacker }} CH _{2}= CH _{2} $

• A. $H _{3} C - C \equiv C - CH _{3}$
• B. $H _{3} C - CH _{2}- C \equiv CH$
• C. $H _{2} C = CH - C \equiv CH$
• D. $HC \equiv C - CH _{2}- C \equiv CH$

Answer 1

Answer: (A)

In Wacker process, alkene is oxidised into aldehyde.

$CH _{2}= CH _{2}+\frac{1}{2} O _{2} \xrightarrow[{ H _{2} O }]{ PdCl _{2} \cdot CuCl _{2}} \underset{\text { (B) }}{ CH _{3} CHO }$

Since on ozonolysis, only alkenes produce aldehydes, 'A' must be an alkene. To decide the structure of alkene that undergoes ozonolysis, bring the products together in such a way that $O$ atoms are face to face and, replace $O$ by double $(=)$ bond. Thus,



Therefore, alkyne must be