Alcohols, Phenols and Ethers – Complete CBSE Class 12 Chemistry Notes

Unit 7 | 6 marks | CBSE 2026–27

1. Alcohols

Alcohols contain an –OH group attached to a saturated carbon. Classification into primary, secondary and tertiary alcohols depends on the carbon bearing the hydroxyl group.

2. Preparation and Reactions

Important preparations include hydration of alkenes and substitution of suitable haloalkanes. Alcohols undergo reactions such as oxidation, dehydration, reaction with sodium and esterification under appropriate conditions.

3. Phenols

Phenol is an aromatic hydroxy compound. Its acidic character is greater than that of ordinary alcohols because the phenoxide ion is resonance-stabilised.

Why is phenol acidic?

Loss of H⁺ produces phenoxide ion. Resonance delocalisation of the negative charge stabilises this conjugate base.

4. Electrophilic Substitution in Phenol

The –OH group activates the ring and directs substitution mainly to ortho and para positions. Bromination and nitration are important examples.

5. Ethers

Ethers contain an oxygen atom bonded to two carbon groups. Williamson ether synthesis is an important preparation method. Ethers can undergo cleavage with strong hydrogen halides under suitable conditions.

6. Comparison Table

📝 Competency Questions

1. Why is phenol more acidic than ethanol?
2. Predict the major orientation of electrophilic substitution in phenol.
3. Choose suitable reagents to convert an alcohol into an alkene.
4. Explain the principle behind Williamson ether synthesis.

🎯 Board Practice

1. Write conversions between alcohols, aldehydes/ketones and alkenes.
2. Explain phenol acidity using resonance.
3. Complete bromination/nitration reactions of phenol.
4. Write Williamson ether synthesis for a specified ether.

MCQs

1. Phenoxide ion is resonance-stabilised. True.
2. Phenol is generally less acidic than ethanol. False.
3. Williamson synthesis is used to prepare ethers. True.
4. The –OH group in phenol directs electrophilic substitution mainly to ortho and para positions. True.

Reaction Map: Alcohols, Phenols and Ethers

Acidity of Phenol

Phenol is more acidic than a typical aliphatic alcohol because the phenoxide ion is resonance-stabilised. This resonance explanation is more important than memorising the comparison alone.

Worked Comparison

When comparing acidity, examine the stability of the conjugate base. Electron-withdrawing groups can stabilise phenoxide and increase acidity, while electron-donating groups generally have the opposite effect.

Preparation & Reactions

• Preparation of alcohols from appropriate halo compounds and alkenes.
• Oxidation and dehydration of alcohols.
• Characteristic reactions of phenol.
• Ether preparation and cleavage.

Common Mistakes

• Confusing phenol with an aromatic alcohol.
• Assuming all alcohols oxidise to the same product.
• Forgetting that phenol’s acidity is connected to resonance stabilisation.

Practice

1. Predict oxidation products of primary and secondary alcohols.
2. Explain the acidity order using resonance.
3. Complete preparation and conversion reactions.
4. Predict products of ether cleavage.

Alcohols, Phenols & Ethers — Reaction Pathways

Acidity of Phenol

Phenol is more acidic than a typical aliphatic alcohol because the phenoxide ion is stabilised by resonance. Electron-withdrawing substituents can further affect acidity.

Important Reactions

Know dehydration of alcohols, oxidation of primary and secondary alcohols, reactions of phenols with electrophiles, and cleavage of ethers. Conditions matter: the same reactant can give different products under different reagents.

Worked Conversion

A primary alcohol can be oxidised first to an aldehyde and, under stronger/continued oxidation, to a carboxylic acid. In a conversion question, select the reagent and conditions according to the required stopping point.

CBSE Practice

1. Arrange compounds according to acidity.
2. Predict products of oxidation and dehydration.
3. Complete phenol reaction sequences.
4. Explain why phenol is more acidic than ethanol.
5. Identify products of ether cleavage.