Question

Give a reaction of alkyne which shows its acidic behaviour

Answer 1

In Alkyne Carbon atoms are SP hybridized so those are more electronegative in nature, So the H attached to the that carbon becomes electropositive and acidic in nature.
Acidity of alkynes is due to their ability to lose hydrogen atom to form alkynideions. Thus, alkynes act as Bronsted-Lowry acids. The triple bonded carbon atom in alkynes is “sp”hybridized. Due to high percentage of “s” character (50%) in alkynes, the “sp” hybridized orbitals of carbon atom in alkynes high electronegativity. These attract the C-H bond of alkynes to a great extent. Thus, alkyne molecules can easily loose hydrogen atom forming alkynide ions. Hence, we can say that hydrogen atom attached to the triply bonded carbon atom is acidic in nature.

The acidity of alkynes is greater than the acidity of alkanes and alkenes as the carbon atom in alkanes and alkenes are “sp3 and “sp2

” hybridized respectively. Hence, these molecules contain lesser percentage of “s” character in comparison to alkynes.Thus, the electronegativity of carbon atom in these cases is lesser than alkynes. Hence, alkanes and alkenes don‘t show the reactions with bases to liberate hydrogen gas. It can further be noted that only hydrogen atom attached to triply bonded carbon atom are acidic not the other hydrogen atoms in the alkyne chain.

Answer 2

Ans: Alkynes show slightly acidic character. 1 – Alkynes behave as weak acids, because of more electronegativity of sp- hybridized carbon (triple bonded carbon).Alkanes and Alkenes does not show this character.
The hydrogen which is attached to triple bonded carbon can lose as H⁺ ion, this is the reason for the weak acidic character of 1- Alkynes.