Question

In the following compounds

the order of acidity is

• A. $3>4>1>2$
• B. $1>4>3>2$
• C. $2>1>3>4$
• D. $4>3>1>2$

Answer 1

The correct option is D $4>3>1>2$

Phenols are ​more acidic than alcohol & water due to
(i) the higher electronegativity of $s{p}^2$ ​carbon to which OH ​group is attached.
(ii) the electron withdrawing nature of the benzene ring​.

Conjugate base of phenol is stabilised by conjugation of negative charge in the ring​. Acidic strength is inversely proportional to EDGs and directly proportional to EWGs.

Between (1), (2) and (3), $N{O}_2$ group is electron withdrawing while $C{H}_3$ group is electron releasing group, so $N{O}_2$ increases acidic nature while $C{H}_3$ decreases it therefore acidity order will be (2)<(1) <(3).

In between meta and para nitrophenol, p-nitrophenol will be stronger acid because the negative charge is resonance stabilised by $N{O}_2$ group at para position. $N{O}_2$ at meta position does not involve in resonance stabilisation of negative charge. Therefore, the correct answer will be:
$4>3>1>2$

Resonating structures of m-nitrophenol-

Resonating structures of p-nitrophenol-