Question

Which among the following phenolic compounds is most acidic in nature?

• A. P-aminophenol
• B. Phenol
• C. m-nitrophenol
• D. p-nitrophenol

Answer 1

The correct option is D p-nitrophenol

Deprotonation of $p-nitrophenol$ gives $p-nitrophenoxide$ ion. The negative charge on $O$ atom is stabilised as strongly electron withdrawing $nitro$ group is present in para position.
This effect is some what less in $m-nitrophenol$ as strongly electron withdrawing $nitro$ group is present in meta position.
In case of $p-aminophenol$, deprotonation gives $p-aminophenoxide$ ion.

The negative charge on $O$ atom is destabilised as electron releasing $amino$ group is present in para position.

$p-nitrophenol$ is most acidic.

Option D is correct.