Question

Which is less acidic than phenol?

• A. Formic acid
• B. Acetic acid
• C. Ethanol
• D. o-methoxy phenol

Answer 1

The correct option is C

Ethanol

The explanation for the correct answer

(C) Ethanol

1. The resonating structures of Phenol is more stabilized by resonance than Ethanol.
2. Phenol and Ethanol both are weak acids but Phenol is more acidic as the Phenoxide ion are resonance stabilized.
3. Ethoxide ions are not stabilized by resonance and thus Ethanol is less acidic than Phenol.

The explanation for the incorrect answer

(A) Formic acid

1. Formic acid is more acidic as in Formic acid there is a resonance because of two Oxygen atoms present which are electronegative.
2. In case of phenols, the resonating structures are not much stable and able to release ${\mathrm{H}}^{+}$and thus Phenols are weaker acids than Formic acid.

(B) Acetic acid

1. Phenol is less acidic than Acetic acid because Acetate ion is more stabilized by resonance than Phenoxide ion.
2. The products of both Acetate ion as well as Phenoxide ion is stabilized by resonance
3. In Acetate ions the resonating structures are contributing equally whereas in Phenoxide ion all resonating structures are not contributing equally.
4. More the contribution to the resonating structure more will be the stability and thus Phenol is less acidic than Acetic acid.

(D) o- methoxy phenol

1. In o- methoxy phenol other than resonance also inductive effect is very strong due to which it becomes more acidic.
2. In case of Phenols the resonating structures are less stable than the resonating structure of o-methoxy phenol.
3. Thus, it is more acidic than Phenol.

Therefore, option C is correct. Ethanol less acidic than Phenol.