Consider the following statements about the acidity of phenols.
(A) In the alkoxide ion, the negative charge is delocalised, while in the phenoxide ion, the negative charge is localised on oxygen.
(B) In phenol, the hydroxyl group is attached to an sp2 hybridised carbon of the benzene ring, which acts as an electron withdrawing group.
(C) Cresols are more acidic than phenol, as the electron releasing methyl group favours the formation of the phenoxide ion.
(D) In substituted phenols, an electron withdrawing group such as the nitro group at the ortho or para position enhances the acidic strength of phenol.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (C) only
Phenol ionises more than an alcohol for two reasons: the sp2 carbon pulls electron density from the oxygen, and the phenoxide ion formed is stabilised by delocalisation of its negative charge over the ring. A substituent that helps this delocalisation raises the acid strength; one that works against it lowers it.
(A) In the alkoxide ion, the negative charge is delocalised, while in the phenoxide ion, the negative charge is localised on oxygen. — Incorrect statement. It is the other way round: the charge is localised on oxygen in the alkoxide ion and delocalised in the phenoxide ion, which makes the phenoxide ion more stable.
(B) In phenol, the hydroxyl group is attached to an sp2 hybridised carbon of the benzene ring, which acts as an electron withdrawing group. — Correct statement. The more electronegative sp2 carbon lowers the electron density on oxygen and makes the O–H bond more polar.
(C) Cresols are more acidic than phenol, as the electron releasing methyl group favours the formation of the phenoxide ion. — Incorrect statement. Electron releasing alkyl groups do not favour the formation of the phenoxide ion, so cresols are less acidic than phenol.
(D) In substituted phenols, an electron withdrawing group such as the nitro group at the ortho or para position enhances the acidic strength of phenol. — Correct statement. At these positions the nitro group helps to spread the negative charge of the phenoxide ion.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “(iii) Acidity of phenols: … The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon of benzene ring which acts as an electron withdrawing group.”
“…In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the charge is delocalised. The delocalisation of negative charge (structures I-V) makes phenoxide ion more stable and favours the ionisation of phenol.”
“In substituted phenols, the presence of electron withdrawing groups such as nitro group, enhances the acidic strength of phenol. This effect is more pronounced when such a group is present at ortho and para positions.” … “On the other hand, electron releasing groups, such as alkyl groups, in general, do not favour the formation of phenoxide ion resulting in decrease in acid strength. Cresols, for example, are less acidic than phenol.”