Give reasons for the following:
o-nitrophenol is more acidic than o-methoxyphenol.
Explain why is ortho nitrophenol more acidic than ortho methoxyphenol?
The nitro group (–NO2) is an electron-withdrawing group. It decreases the density in the O–H bond. Thus, the proton can be easily lost. With the presence of an electron-withdrawing group, the phenoxide ion is more stabilised. Due to the high stability of the phenoxide ion, the acidic nature increases. On the other hand, the methoxy group is an electron-releasing group. It increases the density in the O–H bond. Thus, the proton cannot be given out easily. Thus, the phenoxide ion is less stabilised. Due to this, o-nitrophenol is more acidic than omethoxyphenol.
The nitro-group is an electron-withdrawing group. The presence of this group in the ortho position decreases the electron density in the O−H bond. As a result, it is easier to lose a proton. Also, the o-nitrophenoxide ion formed after the loss of protons is stabilized by resonance. Hence, ortho nitrophenol is a stronger acid.
On the other hand, methoxy group is an electron-releasing group. Thus, it increases the electron density in the O−H bond and hence, the proton cannot be given out easily.
For this reason, ortho-nitrophenol is more acidic than ortho-methoxyphenol.
Video Tutorials For All Subjects
- Chemical Reactions of Alcohols and Phenols - Reactions Involving Cleavage of O–H Bond