Question

The acidity of ortho-nitrophenol is _______ that of ortho-methoxyphenol.

• A. more than
• B. similar
• C. less than
• D. none of these

Answer 1

The correct option is A more than

Due to strong -R and -I effect of the $(-N{O}_2)$ group, electron density in the (O-H) bond decreases and hence the loss of a proton becomes easy. Further, after the loss of a proton, the o-nitrophenoxide ion left behind is stabilised by resonance.o-Nitrophenoxide ion is stabilised by resonance, thereby making o-nitrophenol a stronger acid.

In contrast, due to the +R effect of the $\left(OC{H}_3\right)$ group, it increases the electron-density in the (O-H) bond, thereby making the loss of proton difficult. Furthermore, the o-methoxyphenoxide ion left after the loss of a proton is destabilised by resonance. The two negative charges repel each other, thereby destabilising the o-methoxyphenoxide ion.
Thus, o-nitrophenol is more acidic than o-methoxy-phenol.