Question

Choose the correct statement(s) regarding acidic order:

• A. Phenol is more acidic than benzoic acid
• B. 4-Chlorophenol is more acidic than phenol
• C. 4-methylbenzoic acid is less acidic than benzoic acid
• D. Phenol is less acidic than benzoic acid

Answer 1

Answer: (B), (C), (D)

Phenol is less acidic than benzoic acid

Benzoic acid is a stronger acid than phenol because the benzoate ion is stabilized by two equivalent resonance structures in which the negative charge is present at the more electronegative oxygen atom.
In phenoxide ion, non-equivalent resonating structures are there, and the negative charge is on a less electronegative atom (carbon).

Between phenol and 4-Chlorophenol :
In 4-Chlorophenol , the -I effect is more dominant than the +M effect. So, due to the electron-withdrawing nature of chlorine, the negative charge is more stabilized in 4-Chlorophenol than phenol where no such group is present.
Acidic order :
4-Chlorophenol > Phenol
Between Benzoic acid and 4-methylbenzoic acid
4-methylbenzoic acid shows the +H and +I effect, where +H is more dominant.
Acidic strength is inversely proportional to the +H effect, so 4-methylbenzoic acid is less acidic than benzoic acid