Which is More Acidic: Ethanol or Phenol?

Q: Which is more acidic, Ethanol or Phenol?

Phenol (pKa 10) is more acidic than Ethanol (pKa 16). A lower pKa indicates a stronger acid.

Which is more acidic, Ethanol or Phenol?

Phenol (pKa 10) is about 6 orders of magnitude more acidic than ethanol (pKa 16). The phenoxide ion delocalizes its negative charge into the aromatic ring through resonance, while ethoxide has its charge localized on a single oxygen. Phenol has a pKa of 10, while Ethanol has a pKa of 16.

Molecule A	Ethanol (C₂H₅OH), pKa 16
Molecule B	Phenol (C₆H₅OH), pKa 10
More Acidic	Phenol
Governing Factor	Resonance
Difficulty	Intermediate

Introduction

Both ethanol and phenol have an O-H group that can donate a proton. But phenol is a significantly stronger acid. The difference comes down to what happens to the conjugate base.

Acidic Protons

The acidic proton in each molecule is the hydrogen on oxygen (the O-H). Ethanol has a simple alkyl group attached to oxygen, while phenol has an aromatic benzene ring directly bonded to oxygen.

Governing Factor: Resonance

The key factor is resonance. In phenoxide (the conjugate base of phenol), the negative charge on oxygen can delocalize into the aromatic ring through pi overlap. This spreads the charge across multiple atoms. Ethoxide has no such option.

Conjugate Base Stability

Ethoxide (CH3CH2O-) has its negative charge stuck on one oxygen atom. Phenoxide (C6H5O-) can push its charge into the ring, distributing it across the oxygen and several ring carbons. This delocalization provides significant stabilization.

pKa Comparison

Phenol has a pKa of 10 and ethanol has a pKa of 16. The 6-unit difference means phenol is about one million times more acidic, entirely because of resonance stabilization of phenoxide.

Interactive side-by-side 3D viewer with acidic proton highlights, conjugate base overlays, and pKa labels.

Compare Ethanol and Phenol in 3D