Chapter 7 — Alcohols, Phenols and Ethers

Chapter 7 of the Class 12 Chemistry NCERT textbook, "Alcohols, Phenols and Ethers", covers their classification, IUPAC nomenclature, preparation methods, physical properties, and chemical reactions including acidity, esterification, dehydration, oxidation, and electrophilic aromatic substitution.

• Three related oxygen-containing families — The chapter groups alcohols and phenols, both bearing an –OH group on aliphatic versus aromatic carbon, with ethers carrying an R–O–R linkage, and classifies each by structure so their shared and contrasting chemistry can be organised.
• Building them and the role of hydrogen bonding — Multiple preparation routes — from alkenes, carbonyls, Grignard reagents, haloarenes, diazonium salts and cumene — are surveyed, while hydrogen bonding is used to explain the physical properties such as high boiling points and solubility.
• Acidity and characteristic reactions — The chapter compares the acidity of alcohols and phenols and works through their key reactions — esterification, dehydration, oxidation, and the electrophilic substitution that an activating –OH group directs on aromatic rings and aryl ethers.

1. 01Alcohols are classified as primary, secondary or tertiary based on the carbon bearing the –OH group, and as monohydric, dihydric or trihydric based on the number of –OH groups.
2. 02Phenols are stronger acids than alcohols (phenol pKa ≈ 10.0; ethanol pKa ≈ 15.9) because the phenoxide ion is stabilised by delocalisation of the negative charge into the aromatic ring.
3. 03Alcohols are prepared by acid-catalysed hydration of alkenes (Markovnikov addition), hydroboration-oxidation (anti-Markovnikov), reduction of aldehydes/ketones/carboxylic acids, and reaction of Grignard reagents with carbonyl compounds.
4. 04Phenols are prepared industrially from cumene (cumene hydroperoxide route), and in the laboratory from haloarenes (fusion with NaOH), benzenesulphonic acid, or diazonium salts.
5. 05Ethers are synthesised by dehydration of primary alcohols at 413 K or by Williamson synthesis (SN2 reaction of sodium alkoxide with a primary alkyl halide); Williamson synthesis also works for unsymmetrical ethers.
6. 06The –OH group in phenol activates the benzene ring toward electrophilic substitution and directs incoming groups to ortho and para positions; reactions include nitration (giving picric acid with conc. HNO3), halogenation, Kolbe's reaction, and Reimer-Tiemann reaction.