Intermediate Topic 797 of 1102 Organic Chemistry
Phenols
Compounds with OH attached to an aromatic ring, more acidic than alcohols.
In-depth explanation of Phenols
Phenols are compounds in which an OH group is bonded directly to a carbon of an aromatic ring. Phenol is considerably more acidic than typical alcohols, with a pKa of about 10, because the phenoxide ion is stabilized by resonance delocalization of its negative charge into the ring. The OH group is a strong activating substituent that donates electron density to the ring by resonance, so phenols undergo electrophilic substitution much more readily than benzene. Phenol gives a characteristic violet colour with iron(III) chloride, which is used as a diagnostic test.
Going deeper: Phenols
Key ideas: Phenol is acidic (pKa about 10) because the phenoxide ion is resonance stabilised, much stronger than ethanol (pKa 16) but weaker than carbonic acid, so it dissolves in NaOH but not NaHCO3. The OH is a strong ortho and para activator: bromine water gives 2,4,6-tribromophenol instantly. Reactions: Kolbe (salicylic acid), Reimer-Tiemann (salicylaldehyde), FeCl3 violet colour test.
Common mistakes and connections: Students expect phenol to react with NaHCO3 and release CO2, which carboxylic acids do but phenols do not. Another error is thinking the C-O bond breaks easily; it has partial double-bond character. Links to resonance, aspirin synthesis and nitro groups (picric acid is very acidic).
Visualization of Phenols
Phenol (pKa 10) is far more acidic than aliphatic alcohols (pKa about 16) because the phenoxide is stabilized by resonance into the ring. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Bromine water reacts with phenol at room temperature to give a white precipitate of 2,4,6-tribromophenol.
Frequently asked questions about Phenols
What is Phenols?
Compounds with OH attached to an aromatic ring, more acidic than alcohols.
Is Phenols a beginner, intermediate or advanced topic?
Phenols is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Phenols?
Study these earlier topics in Organic Chemistry first: Oxidation of Alcohols, Lucas Test, Ethanol Production.
What comes after Phenols?
The next topics in Organic Chemistry are Ethers and Williamson Ether Synthesis.
Can I practise Phenols with quizzes?
Yes. The interactive lesson includes a self-check question on Phenols, and the Organic Chemistry quiz draws on every topic in this area.
Where Phenols fits in Organic Chemistry
Phenols is topic 69 of 148 in Organic Chemistry.