Question

Among the following, which is least acidic ?

• A. phenol
• B. $o$-cresol
• C. $p$-nitrophenol
• D. $p$-chlorophenol

Answer 1

Answer: (B)

$o$-cresol

Answer 2

When an electron attracting group (like $-NO_2, -Cl$ ) is attached to the phenol ring, it stabilises the negative charge on the oxygen of phenoxide ion. Due to this reason acidic character of phenol increases. But when an electron donating group (like $-CH_3$ ) is attached to the phenol ring, it destabilises the ring and hence , acidic characte r of phenol decreases . Thus, the correct order of acidic character is $p$ -nitrophenol $> p$ -chlorophenol $>$ phenol $> o$ -cresol