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Alcohols, Phenols and Ethers

Chemistry · Class 12NCERT pp. 193–2202 sets × 25 questions

Key facts and formulas for Alcohols, Phenols and Ethers, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.

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Formula sheet for this chapter

IdeaRule or fact
Acidity orderPhenol (pKa 10) > water (15.7) > primary alcohol > secondary > tertiary. Nitro groups at o/p raise acidity most.
Preparation of alcoholsHydration (Markovnikov), hydroboration–oxidation (anti-Markovnikov), Grignard + carbonyl, NaBH₄/LiAlH₄ reduction, ester + 2H₂ → two alcohols.
Grignard + carbonylHCHO → primary; other aldehydes → secondary; ketones → tertiary; ethylene oxide → primary with two extra carbons.
Lucas testTertiary: immediate turbidity; secondary: about 5 minutes; primary: none at room temperature.
Dehydration443 K, conc. H₂SO₄ → alkene; 413 K with excess alcohol → ether. Ease: 3° > 2° > 1°.
Oxidation1° alcohol → aldehyde → acid; 2° → ketone; 3° resists (dehydrates over Cu, 573 K).
Na with OH2 R–OH + 2Na → 2 R–ONa + H₂. Moles of H₂ = (moles of OH) ÷ 2; 1 mol gas = 22.4 L at STP.
Phenol reactionsKolbe: salicylic acid; Reimer–Tiemann: salicylaldehyde; Zn dust: benzene; oxidation: benzoquinone; FeCl₃: violet.
EthersWilliamson (SN2): use a primary halide. HI cleaves aryl alkyl ether to phenol + alkyl iodide. Old ether forms explosive peroxides.
Boiling point and H-bondingMore OH groups, higher boiling point. o-Nitrophenol (intramolecular) is steam volatile; p-nitrophenol (intermolecular) is not.

Three sample questions

Q1. In which compound is the OH attached to an sp² carbon?
  1. C₆H₅CH₂OH
  2. C₆H₅OH
  3. CH₂=CHCH₂OH
  4. cyclohexanol
Hint and solution

Hint: Phenols have OH directly on a benzene ring carbon. Check which carbon each OH is bonded to.

  1. Phenol: C(sp²)–OH — Find the carbon holding the OH in each compound and check its hybridisation.
  2. Benzyl, allyl, cyclohexanol: C(sp³)–OH — In benzyl alcohol and allyl alcohol the OH is on a CH₂ carbon. In cyclohexanol the ring is saturated. All three are sp³.
  3. Only phenol has OH on sp² carbon — In phenol the OH is on a benzene ring carbon, which is sp². So the answer is phenol, Option B.
Answer: B. Phenol has OH on a ring carbon. The others have OH on sp³ carbons.
Q2. The IUPAC name of glycerol is
  1. propan-1,2,3-triol
  2. propane-1,3-diol
  3. propan-1-ol
  4. propane-1,2,3-triol
Hint and solution

Hint: Glycerol has three OH groups on a three carbon chain. Remember when the final e of alkane is kept.

  1. Glycerol: HOCH₂–CH(OH)–CH₂OH — Glycerol has three carbons, each carrying one OH group.
  2. Parent: propane, suffix: triol — Three OH groups mean the suffix is triol. The locants are 1, 2, 3.
  3. Keep e before a consonant — The final e of propane is dropped only before a vowel. Triol begins with t, so e stays: propane-1,2,3-triol. Option D.
Answer: D. Keep the e before a consonant (t of triol).
Q3. C₆H₅OC₂H₅ is named
  1. ethoxybenzene
  2. methoxybenzene
  3. phenoxyethanol
  4. ethylphenol
Hint and solution

Hint: In IUPAC names of ethers the larger group is the parent and the smaller one becomes an alkoxy prefix.

  1. Ar–O–R: larger group = parent — Identify the two groups on oxygen: phenyl and ethyl. Phenyl (benzene) is the larger group.
  2. C₂H₅O– = ethoxy — The smaller group with the oxygen becomes the prefix ethoxy.
  3. Name: ethoxybenzene — Put the prefix before the parent. The answer is ethoxybenzene, Option A.
Answer: A. Larger group (benzene) is the parent. The ethoxy group is the prefix.

How to use this chapter

Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.

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