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. $(IV) > (III) > (II) > (I)$

Answer 1

Answer: (C)

$(III) > (IV) > (II) > (I)$

Answer 2

The correct order of decreasing acidity is
$\underset{(III)}{\mathop{CH\equiv CH}}\,>\underset{(IV)}{\mathop{CH\equiv C-C{{H}_{3}}}}\,>\underset{(II)}{\mathop{C{{H}_{2}}=C{{H}_{2}}}}\,$
$>\underset{(I)}{\mathop{C{{H}_{3}}-C{{H}_{3}}}}\,$
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.