Question

The most reactive hydrocarbon is:

• A. methane
• B. ethane
• C. ethylene
• D. acetylene

Answer 1

Answer: (C)

ethylene

Answer 2

In ethylene $H _{2} C = CH _{2}$, the $C - C$ bond distance is $1.34 \,?$, therefore, the $\pi$ electrons of the double bond are easily exposed to the reactant (electrophiles) which readily react. In acetylene molecule $H - C \equiv C - H$, although there are two $\pi$ bonds but these electrons arc not exposed to the attacking reagents due to small bond distance of $C \equiv C$ bond $(1.20 \,?)$. A catalyst mercuric ion is therefore needed in reactions with actylene.