Question

Which of the following alkynes is most acidic?

• A. $C{H}_{3}C\equiv CH$
• B. $C{H}_{3}C\equiv CC{H}_3$
• C. $C{H}_{3}C{H}_{2}C\equiv CH$
• D. $CH\equiv CH$

Answer 1

The correct option is D $CH\equiv CH$

Compound (b), But 2-yne has no hydrogen attached to sp hybridised carbon. Thus it lacks acidic hydrogen, so all other compounds are more acidic than it.
In compound (c) and (a) i.e., But-1-yne and Propyne has methyl groups which shows + I effect attached to triple bond. As the number of groups which gives + I effect increases, acidic character decreases. $(C{H}_3\to$ gives +I effect)
Thus, ethyne does not have any +I group and it has two sp hydridised hydrogen atom which make it most acidic of all four compounds.