question_answer

The correct order of decreasing acidity of nitrophenols will be

A)  m- nitrophenol>p-nitrophenol>o-nitrophenol

B)  o-nitrophenol >m-nitrophenol> p-nitrophenol

C)  p-nitrophenol>m-mtrophenol> o-nitrophenol

D)  p-nitrophenol > o-nitrophenol > m-nitrophenol

Correct Answer: D

Solution :

                 \[-\text{N}{{\text{O}}_{\text{2}}}\]group at \[\text{o}-\]and p- position withdraws electrons of the O?H bond towards itself by the stronger -R effect while the \[-\text{N}{{\text{O}}_{\text{2}}}\] group at m-position with draws electrons of the O?H bond by the weaker -I effect. Thus, o- and p- nitrophenols are more acidic than m- nitrophenol. Among o- and p- nitrophenols, o- nitrophenol is little less acidic   than   p-nitrophenol   due   to intramolecular H-bonding which makes loss of a proton little more difficult. \[\therefore \]The order of acidity of nitrophenols is p-   nitrophenol   >   o-nitrophenol   > m-nitrophenol