Question

The correct decreasing order of the acidic strength of the given compound is :

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

Answer 1

The correct option is A (I)> (II)> (III)> (IV)

$N{O}_2$ group being highly $EWG$ $(e^{-}$ withdrawing group$)$ makes the ring $e^{-}$ deficient.

Due to the presence of nitro group on ortho position, the $-COOH$ group bends out of the plane of the ring due to steric hindrance.

As a result, $H^{+}$ ion can be easily removed because it has come out of plane of ring.

Any group attached at ortho position may be $EWG$ or $EDG$ is more acidic than benzoic acid due to the ortho effect.

Further, O-methoxybenzoic acid is more stronger than O-hydroxybenzoic acid as methoxy $(-OC{H}_3)$ group being $e^{-}$ donating group and it decreases the probability of release of $H^{+}$ ion but in O-hydroxybenzoic acid $H-$ bond is formed making the compound stable hence less acidic than O-methoxybenzoic acid.

Hence the correct option is A.