Alcohol, Phenol and Ethers Class 12 One Shot | CBSE 12th Chemistry Chapter-7 Revision | CBSE 2025-26

Understanding Alcohols, Phenols, and Ethers: Structure, Properties, and Reactions

Alcohols, Phenols, and Ethers are three important classes of oxygen-containing organic compounds that form a significant part of the CBSE Class 12 Chemistry curriculum. In alcohols, the hydroxyl (–OH) functional group is bonded to a saturated carbon atom. Phenols have the –OH group directly attached to an aromatic benzene ring, giving them distinctly different acidity and reactivity compared to alcohols. Ethers, on the other hand, have an oxygen atom bridging two alkyl or aryl groups, represented by the general formula R–O–R'. This chapter provides a comprehensive study of their classification, methods of preparation, physical properties, chemical reactions, and their importance in daily life and industry.

Alcohols are classified as monohydric, dihydric, or trihydric based on the number of –OH groups, and as primary (1°), secondary (2°), or tertiary (3°) based on the carbon atom to which the –OH group is attached. In primary alcohols, the hydroxyl-bearing carbon is bonded to only one other carbon atom; in secondary alcohols, it is bonded to two; and in tertiary alcohols, to three. This classification is not merely structural — it profoundly influences chemical behaviour. For example, primary alcohols undergo oxidation first to aldehydes and then to carboxylic acids, secondary alcohols oxidise to ketones, and tertiary alcohols generally resist oxidation under mild conditions. The Lucas test — using concentrated hydrochloric acid and zinc chloride — exploits these reactivity differences: tertiary alcohols form a turbid layer almost immediately, secondary alcohols react within five to ten minutes, and primary alcohols show no reaction at room temperature. The preparation of alcohols includes the hydrolysis of alkyl halides, hydration of alkenes, reduction of carbonyl compounds, and the industrial fermentation of sugars for ethanol production.

Phenols are distinctly more acidic than alcohols, with a pKa of approximately 10 compared to 16 for typical alcohols. This enhanced acidity arises because the phenoxide ion formed after deprotonation is stabilised by resonance delocalisation of the negative charge into the aromatic ring. This same resonance makes the –OH group in phenols a strongly activating group for electrophilic aromatic substitution reactions. Phenol undergoes bromination, nitration, and sulphonation much more readily than benzene. The Reimer–Tiemann reaction introduces a formyl group ortho to the –OH group, yielding salicylaldehyde — a precursor to aspirin. Ethers are generally less reactive than alcohols and phenols but can be cleaved by strong acids like HI or HBr to produce alkyl halides and alcohols or phenols. The Williamson ether synthesis, which involves the reaction of an alkoxide with an alkyl halide, is the most widely used laboratory method for preparing ethers. Industrially, diethyl ether is a common solvent, and anisole (methoxybenzene) is used in perfumery. This chapter also covers important tests such as the iodoform test for ethanol and the ferric chloride test for phenols, equipping students with both theoretical knowledge and practical analytical skills for board examinations and competitive entrance tests like JEE and NEET.

• Alcohols contain the –OH functional group on a saturated carbon; phenols have –OH directly on an aromatic ring; ethers have an oxygen bridging two carbon groups.
• Primary (1°), secondary (2°), and tertiary (3°) alcohols differ in oxidation products and Lucas test reactivity — tertiary alcohols react fastest.
• Phenols are more acidic than alcohols because the phenoxide ion is stabilised by resonance delocalisation into the aromatic ring.
• The –OH group in phenols is a strongly activating, ortho-para directing group for electrophilic aromatic substitution reactions.
• Ethers are cleaved by concentrated HI or HBr; the Williamson ether synthesis is the most important method for preparing unsymmetrical ethers.