Identify the correct set from the following Compound $p K_a \quad$ Compound $p K_a$
Identify the correct set from the following
Compound $p K_a \quad$ Compound $p K_a$
$m$-nitrophenol 10.2
o-nitrophenol 10.2
$m$-nitrophenol 7.2
o-nitrophenol 7.2
Solution
In $o$-nitrophenol there is intramolecular $\mathrm{H}$-bonding, since $-\mathrm{NO}_2$ group is very close to - $\mathrm{OH}$ group. Thus, proton can not be easily released from $o$-nitrophenol as compared to para and meta. Thus, $\mathrm{p} K_a$ is least.