Question

Electrophilic addition reaction is easily given by

• A. acetylene
• B. ethene
• C. ethane
• D. benzene

Answer 1

Answer: (B)

ethene

Answer 2

Inspite of the fact that the two $\pi$-bonds are present in alkynes, these are less reactive than alkenes towards addition reactions (due to symmetrical cylindrical nature of $\pi$ - electron cloud). Further, alkynes do not show geometrical isomerism due to their linear structure The $\pi$- electrons of alkynes are more tightly attached to the carbon atoms than $\pi$-electrons in alkene and hence less easily available for addition reactions with electrophiles. As a result, alkynes are less reactive than alkenes towards electrophilic addition reaction. A majority of addition reactions of alkynes are catalysed by heavy metal ions such as $Hg^{2+}$ and $Ba^{2+}$, etc., while no such catalysts are needed in case of electrophilic addition reactions to alkenes