Question

Which of the following alkynes is least 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 B $C{H}_{3}C\equiv CC{H}_3$

But-2-yne has no hydrogen attached to sp hybridised carbon. So all other compounds are more acidic than it and is least acidic.
But -1-yne and Propyne have groups having + I effect ($C{H}_3\to$ give + I effect) attached to triple bond. As the number of groups which give +1 effect increases, acidic character decreases.
Acetylene is most acidic among all.
Hence correct option is b.