Alkynes are acidic in nature, whereas alkenes and alkanes are not. Explain.

The acidic character of alkynes can be explained by the concept of orbital electronegativity. The triple bonded carbon atoms of alkynes use two sp hybridised orbitals in the formation of σ bonds.



The carbon atoms of alkynes have greater s-character as compared to the double bonded carbon atoms of alkenes and singly bonded carbon atoms of an alkane. Now s-orbital penetrates more towards the nucleus, the electrons in it are more tightly held. The carbon atoms of the ( C ≡ C) triple bond become more electronegative than sp² and sp³ hybridised carbon atom. The more electronegative carbon atom thus attracts the shared pair of electrons more strongly. As a result, a proton is easily knocked out from – C ≡ C – H as compared to  and , hence acidic character. CH₃ – C ≡ – CH₃(But-2-yne) is not acidic because it does not contain any hydrogen attached to triple bonded carbon atom.