ChemistryCHEM 11
Alcohols, Phenols & Ethers
Acidity order, Lucas test, Williamson synthesis, Kolbe reaction, Reimer-Tiemann
Concept Core
Essential theory — everything NCERT tests on Alcohols, Phenols & Ethers
ALCOHOLS — CLASSIFICATION & PROPERTIES
1° (methanol, ethanol), 2° (propan-2-ol), 3° (tert-butanol). Acidity: 1° > 2° > 3° (electron-donating alkyl groups destabilise alkoxide). Boiling point: 1° > 2° > 3° (H-bonding and branching).
Lucas test: 3° reacts immediately (turbidity), 2° reacts in 5 min, 1° doesn't react at room temp. Reagent: ZnCl₂/HCl (conc.).
REACTIONS OF ALCOHOLS
Dehydration → alkenes (POCl₃/pyridine preferred; H₂SO₄ at 170°C). Esterification with carboxylic acids (H⁺/H₂SO₄). Oxidation: 1° → aldehyde → carboxylic acid; 2° → ketone; 3° resistant to mild oxidation.
Victor Meyer test: distinguishes 1°, 2°, 3° alcohols by nitroalkane colour.
PHENOLS
Phenol (C₆H₅OH): acidic (pKa ≈ 10). Stronger acid than alcohols but weaker than carboxylic acids. O-H more acidic due to phenoxide ion stabilisation by resonance.
Kolbe reaction: phenol + CO₂ (NaOH, pressure, heat) → salicylic acid. Reimer-Tiemann: phenol + CHCl₃ + KOH → o-hydroxybenzaldehyde (salicylaldehyde). Electrophilic substitution at o and p positions (ring activated by -OH).
ETHERS
R-O-R'. Relatively inert. Cleavage by HI (strongest). Formed by Williamson synthesis: R-O⁻Na⁺ + R'X → R-O-R' + NaX. Favoured by 1° alkyl halide (SN2).
Anisole (methoxybenzene): undergoes EAS at o and p positions. Diethyl ether: common solvent, flammable, forms peroxides on long storage.
Fact & Formula Vault
High-yield facts, numbers, and formulas
Acidity Order
Phenol > 1° alcohol > 2° > 3°
Resonance stabilises phenoxide
pKa phenol ≈ 10 (weaker acid than RCOOH)
Electron-withdrawing groups increase phenol acidity
Key Reactions
Lucas test: ZnCl₂/HCl (3°>2°>1°)
Kolbe: phenol + CO₂ → salicylic acid
Reimer-Tiemann: phenol + CHCl₃/KOH → o-OH-benzaldehyde
Williamson: RO⁻Na⁺ + R'X → ether
Oxidation Products
1° alcohol → aldehyde → acid
2° alcohol → ketone
3° alcohol: no mild oxidation
KMnO₄ oxidises 1° → acid
Worked Examples
NEET-style questions solved step-by-step
EASYLucas test: 2-butanol gives turbidity within 5 minutes. This is because:▾
Lucas test: 2-butanol gives turbidity within 5 minutes. This is because:
2-butanol is a secondary (2°) alcohol. 2° alcohols react with Lucas reagent (ZnCl₂/conc. HCl) within ~5 minutes. 3° reacts immediately. 1° doesn't react at room temperature.
MEDIUMKolbe reaction of sodium phenoxide gives:▾
Kolbe reaction of sodium phenoxide gives:
Sodium phenoxide + CO₂ under pressure → sodium salt of 2-hydroxybenzoic acid (salicylic acid). This is the industrial route to salicylic acid (aspirin precursor).
HARDWilliamson synthesis of methyl phenyl ether (anisole). Which reagent combination works best?▾
Williamson synthesis of methyl phenyl ether (anisole). Which reagent combination works best?
Sodium phenoxide (C₆H₅O⁻Na⁺) + CH₃I (methyl iodide) → C₆H₅OCH₃ (anisole) + NaI. Use 1° alkyl halide (SN2). Tertiary alkyl halides undergo elimination instead.
Mistake DNA
Common NEET traps for this chapter
⚠ Acidity of alcohols
Alcohols: 1° > 2° > 3° for acidity. More alkyl groups = more electron donation to O = destabilises O⁻. Counter-intuitive: more substituted = LESS acidic.
✓ Fix: 1° alcohol is more acidic than 3° alcohol.
⚠ Phenol vs alcohol acidity
Phenol is MORE acidic than alcohols (but less than carboxylic acids). Phenoxide stabilised by resonance with ring.
✓ Fix: Acid strength: RCOOH > phenol > H₂O > alcohol
⚠ Reimer-Tiemann product
Reimer-Tiemann gives ORTHO product predominantly (also some para). Not meta. The -OH group directs to o/p positions.
✓ Fix: Reimer-Tiemann → salicylaldehyde (o-hydroxy). Not meta.
Chapter Intelligence
Exam data and last-minute strategy
NEET Frequency
2–3 Q/year. Lucas test (3° > 2° > 1°), Kolbe product (salicylic acid), Reimer-Tiemann, Williamson synthesis conditions, acidity order.
High-Yield
3° alcohol: immediate turbidity with Lucas. Kolbe → salicylic acid. Reimer-Tiemann → salicylaldehyde. Williamson: RO⁻Na + 1° RX → ether.
Strategy
Lucas test: know the order and time. Kolbe vs Reimer-Tiemann: know the reagent and product. Acidity order is a 1-mark recall question.
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