CBSE Class 12 Chemistry: Alcohols, Phenols & Ethers — Notes 2026

Classification and Structure of Alcohols

• Primary (1°): −OH on C with 1 alkyl; CH₃OH (methanol), CH₃CH₂OH (ethanol)
• Secondary (2°): −OH on C with 2 alkyls; isopropanol (CH₃CHOHCH₃)
• Tertiary (3°): −OH on C with 3 alkyls; tert-butanol (CH₃)₃COH; cannot be oxidised to aldehyde/ketone

Preparation of Alcohols

• Hydration of alkenes: H₂O + alkene (H₂SO₄ catalyst); Markovnikov's rule applies
• Reduction of carbonyl: NaBH₄ reduces ketone/aldehyde to secondary/primary alcohol; LiAlH₄ stronger, also reduces acids
• Grignard reaction: RMgX + HCHO → 1° alcohol; RMgX + RCHO → 2° alcohol; RMgX + R₂CO → 3° alcohol

Reactions of Alcohols

• With HX: ROH + HX → RX + H₂O; order of reactivity: 3° > 2° > 1° (Lucas test uses ZnCl₂/HCl)
• Oxidation: 1° → aldehyde (mild: PCC) → carboxylic acid (strong: K₂Cr₂O₇/H⁺); 2° → ketone; 3° not easily oxidised
• Dehydration: H₂SO₄, 170°C → alkene (intramolecular) or 140°C → ether (intermolecular)

Phenols — Properties and Reactions

• Phenol: −OH directly on benzene ring; pKa ≈ 10; more acidic than alcohols (pKa ~16)
• Acidity: phenoxide ion stabilised by resonance across ring; electron-withdrawing groups increase acidity
• Reactions: electrophilic aromatic substitution (−OH activates ortho/para); Kolbe's reaction (CO₂ + NaOPh → salicylic acid)

Distinction Between Alcohol and Phenol

• FeCl₃ test: phenol gives violet/purple colour; alcohols give no colour change
• NaOH: phenol dissolves (acidic); alcohols do not react with NaOH
• Na metal: both react, but phenol reacts more vigorously (more acidic)

Ethers

• Ether: R−O−R'; named as alkoxy alkane; dimethyl ether (ethoxyethane); sweet smell, low boiling point
• Williamson synthesis: RO⁻Na⁺ + R'X → R−O−R' + NaX; best method for mixed ethers; SN2 mechanism
• Properties: good solvent (non-polar, dissolves organics); anaesthetic (diethyl ether); highly flammable

CBSE Board Focus

• Alcohols Phenols Ethers: 5–7 marks; Lucas test, FeCl₃ test, Williamson synthesis mechanism
• Comparative acidity: methanol < water < phenol < carbonic acid — explain using resonance and inductive effects
• Reactions of phenol: four key reactions with mechanisms (bromination, nitration, Kolbe's, Reimer-Tiemann)