Question
Alkynes are less reactive towards electrophilic addition reactions than alkenes. Explain.
Solution
In alkynes, the carbon atom is sp hybridised whereas in alkenes, it is sp2 hybridised. The sp hybrid orbitals have greater s-character (50%) and lesser effective size than sp2hybrid orbitals (33.3%). Carbon-carbon triple bond length (– C ≡ C –) is 120 pm while carbon-carbon double bond length (C = C) is 134 pm. Consequently, 
-electrons are more tightly held by the nuclei of carbon atoms in alkyne than in alkene. As a result, the 
electrons are less easily available for combination with the electrophiles. Hence alkynes are less reactive than alkenes.
-electrons are more tightly held by the nuclei of carbon atoms in alkyne than in alkene. As a result, the electrons are less easily available for combination with the electrophiles. Hence alkynes are less reactive than alkenes.
