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Assam ASSEB HS Chemistry study materials
Assam ASSEB HS Chemistry study resources

Assam ASSEB HS Chemistry: Alcohols, Phenols and Ethers

Assam ASSEB HS Chemistry · Work through your exam, one topic at a time.

All guide sections

Alcohols, Phenols and Ethers

What this domain tests

Preparation, classification, characteristic reactions, distinguishing tests and named reactions of alcohols, phenols and ethers.

Core rules

  • Preparation: hydration of alkenes, hydroboration–oxidation (anti-Markovnikov alcohol), Grignard addition to carbonyls, reduction of aldehydes and ketones, and the cumene process for phenol.
  • Lucas test with ZnCl₂ and concentrated HCl: tertiary alcohol gives immediate turbidity, secondary in about five minutes, primary shows no change at room temperature.
  • Oxidation: primary alcohols give aldehydes then acids; PCC stops the oxidation at the aldehyde; tertiary alcohols resist oxidation under ordinary conditions.
  • Dehydration with concentrated H₂SO₄ follows the order 3° > 2° > 1°.
  • Phenol (pKa about 10) is far more acidic than ethanol (about 16) because the phenoxide ion is resonance-stabilised. Electron-withdrawing groups, especially at ortho and para positions, increase acidity further; p-nitrophenol is stronger than phenol.
  • Phenol reactions: bromine water gives 2,4,6-tribromophenol; Kolbe carboxylation (NaOH, CO₂, then H⁺) gives salicylic acid; Reimer–Tiemann (CHCl₃, NaOH) gives salicylaldehyde; FeCl₃ gives a violet colour.
  • Ethers: Williamson synthesis works best with a primary halide; secondary and tertiary halides give elimination. Cleavage with excess HI gives two molecules of alkyl iodide; with one equivalent, the less hindered alkyl iodide forms.

Worked example

Three unlabelled alcohols - propan-1-ol, propan-2-ol and 2-methylpropan-2-ol - are shaken separately with Lucas reagent. The tertiary alcohol turns cloudy at once, the secondary after several minutes, and the primary stays clear unless warmed. The order of carbocation stability, 3° > 2° > 1°, explains the rates.

Traps that cost marks

Lucas reagent is ZnCl₂ in concentrated HCl, not dilute HCl alone. Phenol does not undergo Friedel–Crafts reaction and is not oxidised to an aldehyde by PCC. Williamson synthesis with a tertiary halide gives an alkene, not an ether.