Class 12 Chemistry Alcohols Phenols Ethers Notes - Download PDF

Ans. Chapter 7 carries 4 to 6 marks in the CBSE Class 12 Chemistry board exam, averaged across the last five board papers. The marks are typically split as one 3-mark mechanism or reaction-equation question plus one 2-mark distinguishing-test or short-answer question.

Ans. Phenol is more acidic because the phenoxide ion is resonance-stabilised: the negative charge on the oxygen is delocalised over the ortho and para positions of the benzene ring. The ethoxide ion has no such delocalisation, so it is a less stable conjugate base. As a result, phenol (pK_a approximately 10) is about 10⁶ times more acidic than ethanol (pK_a approximately 16).

Ans. Williamson synthesis prepares ethers by reacting a sodium alkoxide with a haloalkane through an SN2 mechanism. Only primary haloalkanes work because secondary and tertiary substrates undergo E2 elimination with the strong base / strong nucleophile alkoxide, giving alkenes instead of ethers. For an unsymmetrical ether, always derive the alkoxide from the bulkier alkyl group.

Ans. Anisole (C₆H₅-O-CH₃) reacts with concentrated HI to give phenol and methyl iodide. The phenyl-oxygen bond never cleaves because of partial double-bond character from the lone-pair conjugation of oxygen into the ring. The reaction proceeds by SN2 attack of iodide on the methyl carbon.

Ans. Mix the alcohol with the Lucas reagent (concentrated HCl plus anhydrous ZnCl₂) at room temperature. Tertiary alcohols give cloudiness or turbidity immediately because the tertiary carbocation forms fast. Secondary alcohols give turbidity within 5 to 10 minutes. Primary alcohols give no turbidity at room temperature and require heating.

Ans. Reimer-Tiemann gives salicylaldehyde (2-hydroxybenzaldehyde) on treatment of phenol with CHCl₃ and aqueous NaOH followed by dilute acid. Kolbe gives salicylic acid (2-hydroxybenzoic acid) when sodium phenoxide reacts with CO₂ at 400 K and 6 atm, followed by acidification. Both are ortho-substitution reactions on the phenoxide.

Ans. The cumene process oxidises cumene (isopropylbenzene) with atmospheric O₂ to cumene hydroperoxide, then acidifies with dilute H₂SO₄ to give phenol and acetone as the valuable co-product; this is the major industrial route. The Dow process hydrolyses chlorobenzene with NaOH at 623 K and 320 atm followed by acidification, giving phenol; it is an older industrial route that needs extreme temperature and pressure. CBSE always asks you to name acetone as the cumene by-product.

Ans. Hydroboration-oxidation uses B₂H₆ / THF followed by alkaline H₂O₂ and gives the anti-Markovnikov alcohol with syn-addition stereochemistry, no carbocation, no rearrangement. Acid-catalysed Markovnikov hydration uses dilute H₂SO₄ and gives the Markovnikov alcohol via a carbocation intermediate, which may rearrange. Hydroboration is the preferred CBSE 3-mark answer when the question asks for a rearrangement-free preparation of a primary alcohol.

Ans. Picric acid (2,4,6-trinitrophenol) is prepared by stepwise nitration of phenol. Treatment with dilute HNO₃ gives ortho- and para-nitrophenol; further nitration with more concentrated HNO₃ gives 2,4-dinitrophenol; and final nitration with concentrated HNO₃ + H₂SO₄ gives picric acid. With pK_a 0.4, picric acid is stronger than acetic acid because three -NO₂ groups stabilise the conjugate base by resonance and -I.

Ans. Saytzeff's rule says that in an E1 dehydration, the more-substituted alkene (the more stable one) is the major product. For 2-methylbutan-2-ol with conc. H₂SO₄ at 443 K, the major product is 2-methylbut-2-ene (trisubstituted), not 2-methylbut-1-ene. Alkene stability follows hyperconjugation: more alpha-H atoms means more hyperconjugative stabilisation.

Ans. PCC (pyridinium chlorochromate) in dichloromethane is a mild non-aqueous oxidant; it abstracts only the alpha-H and stops at R-CHO because the aldehyde is not soluble in CH₂Cl₂ to undergo further oxidation. KMnO₄ is a strong aqueous oxidant: the aldehyde hydrates to R-CH(OH)₂ in water, and further oxidation of the hydrate gives R-COOH. The Collegedunia notes flag PCC as the only "stop-at-aldehyde" reagent.

Ans. You can download the complete 23-page Class 12 Chemistry Chapter 7 Notes PDF for free from the download card at the top of this page. The PDF is mapped to the 2026-27 NCERT print and includes all named reactions (Lucas, Williamson, Reimer-Tiemann, Kolbe, cumene, Dow), full mechanisms, distinguishing tests (Lucas, Victor-Meyer, ferric chloride, iodoform), and a quick-recall summary on the last page.