Question

The correct order of acid strength of the following compounds is

(i) Phonol

(ii) p-cresol

(iii) m-nitrophenol

(iv) p-nitrophenol

(a) III > II > I > IV

(b) IV > III > I > II

(c) II > IV > I > III

(d)  I > II > IV > III

Answer 1

Correct Option (b) IV > III > I > II

Explanation:

Acidic due to resonance stabilisation of phenoxide ion.

NO₂ withdraws electrons, stabilises the phenoxide ion, hence acidity is increased. 

(iv) Lower acidity in case of meta-isomer as compared to para-isomer is explained by the fact that m-nitrophenoxide is stabilised by inductive effect only and no resonance effect operates with -NO₂ group.

Thus, m-nitrophenol < p-nitrophenol (acidic) 

(iii)           (iv)

Thus, correct order is iv > III > I > III