Chapter 7 — Alcohols, Phenols and Ethers

Class 12 Chemistry Chapter 7 covers alcohols, phenols and ethers — their classification, IUPAC nomenclature, preparation methods, physical properties, and chemical reactions including acidity, esterification, dehydration, oxidation, and electrophilic aromatic substitution.

Alcohols, phenols and ethers are fundamental organic compound classes studied in NCERT Class 12 Chemistry Chapter 7. Alcohols and phenols both contain an –OH group attached to aliphatic and aromatic carbon atoms respectively, while ethers contain an alkoxy or aryloxy group (R–O–R). The chapter covers IUPAC nomenclature, classification into primary/secondary/tertiary and mono/di/trihydric types, preparation from alkenes, carbonyl compounds, Grignard reagents, haloarenes, diazonium salts and cumene, physical properties governed by hydrogen bonding, and chemical reactions such as acidity, esterification, dehydration, oxidation, and electrophilic substitution on phenols 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.