Among the following four compounds A. Phenol B. Methyl phenol C. meta-nitrophenol D. para nitrophenol the…
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
An electron withdrawing group (-I showing group like $\left.-\mathrm{NO}_2,-\mathrm{CN}\right)$ stabilises the phenoxide ion, thus when present, increases the acidity of phenol. On the other hand electron releasing groups ($+I$ showing group like $-\mathrm{CH}_3,-\mathrm{C}_2 \mathrm{H}_5$), when present, decrease the acidity of phenol by destabilising phenoxide ion. Hence, the correct order of acidity of given compounds is
\(\underset{(D)}{\text{p-nitrophenol}} > \underset{(C)}{\text{m-nitrophenol}} > \underset{(A)}{\text{phenol}} > \underset{(B)}{\text{methyl phenol}}\)
(due to intermolecular H -bonding)