Answer the question on the basis of passage given below:
Strong oxidizing agents, oxidize toluene and its derivatives to benzoic acid. However, it is possible to stop the oxidation at the aldehyde stage with suitable reagents that convert methyl group to an intermediate that is difficult to oxidize further.
Decreasing order of acidic strength will be:
A. Phenol
B. 2-Methyl phenol
C. 3-Methyl phenol
D. 4-Methyl phenol
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A > C > D > B
A phenol is acidic because its phenoxide ion is stabilised by delocalisation of the negative charge over the ring. A methyl group releases electrons; it destabilises the phenoxide ion and so lowers the acid strength. The effect is stronger at the ortho and para positions, where the negative charge of the phenoxide ion is delocalised:
(A) Phenol (no substituent) is the strongest acid.
(C) 3-Methylphenol: the meta \( \ce{CH3} \) acts only through a weak inductive effect, so it is only slightly weaker.
(D) 4-Methylphenol: the para \( \ce{CH3} \) pushes electron density onto the carbon carrying the charge, so it is weaker still.
(B) 2-Methylphenol: the ortho \( \ce{CH3} \) acts strongly and, being next to the –OH group, also hinders solvation of the phenoxide ion, so it is the weakest.
NCERT (2026-27 edition):
Acidity of Phenols – “… 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. It is due to the effective delocalisation of negative charge in phenoxide ion when substituent is at ortho or para position. 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.”