Question

Among the following which is least acidic?

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

Answer 1

The correct option is D

o-cresol

Explanation for correct option:

D. o-cresol

Phenol:

• Phenol is an aromatic organic compound with a molecular formula ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{OH}$.
• The molecule consists of a phenyl group $(-{\mathrm{C}}_6{\mathrm{H}}_5)$ bonded to a hydroxy group $(-\mathrm{OH})$.
• o-cresol contains an alkyl group$\left({\mathrm{CH}}_3\right)$, which is an electron-releasing group, so the alkyl group destabilizes the phenoxide ion by intensifying the negative charge, so this will decrease the acidic character and this is a weak acid.

Structure of o-cresol:

Expalantion for incorrect options:

A. Phenol

• Phenol is more acidic than o-cresol.

B. p-chlorophenol

• In p-chlorophenol, the electron-withdrawing groups$\left(\mathrm{Cl}\right)$ will stabilize the phenoxide ion by charge dispersal through a powerful electron-withdrawing (-I) inductive effect. Thus, it is more acidic than o-cresol.

C. p-nitrophenol

• In p-nitrophenol, the electron-withdrawing groups$\left({\mathrm{NO}}_2\right)$ will stabilize the phenoxide ion by charge dispersal through a powerful electron-withdrawing (-I) inductive effect.

Thus, it is more acidic than o-cresol.

Hence, the correct option is D i.e. o-cresol.