Question
Among the following four compounds
A) Phenol
B) Methyl Phenol
C) meta - nitrophenol
D) para-nitrophenol
the acidity order is
-
D > C > A > B
-
C > D > A> B
-
A > D > C > B
-
B > A > C> D
Solution
A.
D > C > A > B
An electron withdrawing group (-I showing group like -NO2, -CN) stabilises the phenoxide ion, thus when present, increases the acidity of phenol. On the other hand, the electron releasing groups (+I showing group like -CH3, -C2H5), when present, decrease the acidity of phenol by destabilising phenoxide ion. Hence, the correct order of acidity of given compound is
p-nitrophenol > m-nitrophenol > phenol > methyl phenol
