Question

The decreasing order of acidic character among ethane $(I)$, ethene $(II)$, ethyne $(III)$ and propyne $(IV)$ is

• A. $(I)>(II)>(III)>(IV)$
• B. $(II)>(III)>(I)>(IV)$
• C. $(III)>(IV)>(II)>(I)$
• D. $(IV)>(III)>(II)>(I)$
• E. $(III)>(IV)>(I)>(II)$

Answer 1

Answer: (C)

The correct order of decreasing acidity is
$\underset{(III)}{CH\equiv CH}>\underset{(IV)}{CH\equiv C-C{H}_3}>\underset{(II)}{C{H}_2=C{H}_2}$
$>\underset{(I)}{C{H}_3-C{H}_3}$
Hydrogen atoms attached to sp-hybridised carbon atom are most acidic, followed by those attached to $s{p}^2$ hybridised carbon atom and those attached to $s{p}^3$ hybridised carbon are least acidic.