The complete lecture — the chemistry comes alive in the live panel as you read. Scroll down; the animation keeps pace, and you can run the oxidation ladder yourself.
1 — Classifying alcohols
- Alcohol — the –OH group on a saturated carbon (R–OH). It is 1°, 2° or 3° depending on how many carbons the –OH carbon touches.
2 — Preparation
Four routesCH₂=CH₂ + H₂O →[H⁺] C₂H₅OH · R–X + KOH(aq) → R–OH
CH₃CHO + 2[H] → C₂H₅OH · C₆H₁₂O₆ →[yeast] 2C₂H₅OH
3 — Physical properties & hydrogen bonding
- Hydrogen bonding — the polar –OH lets molecules bridge as O–H···O, raising boiling points and giving water-solubility.
4 — Reactions of alcohols
Three key reactions2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
C₂H₅OH →[conc.H₂SO₄,170°C] CH₂=CH₂ + H₂O
5 — The oxidation ladder
Ladder1° → aldehyde → acid · 2° → ketone · 3° → resists
Acidified K₂Cr₂O₇ oxidises 1° and 2° alcohols (turning orange → green); 3° alcohols have no H on the –OH carbon, so they resist. Move the sliders to climb the ladder.
6 — Distinguishing tests
| Alcohol | Lucas reagent |
|---|
| 3° | cloudy immediately |
| 2° | cloudy ~5 min |
| 1° | no change (RT) |
Also: K₂Cr₂O₇ orange→green for 1°/2°; iodoform (yellow CHI₃) for ethanol & CH₃CH(OH)–.
7 — Phenols
- Phenol — –OH on a benzene ring. More acidic than alcohols (resonance-stabilised phenoxide), weaker than carboxylic acids. Gives a violet colour with FeCl₃.
Aciditycarboxylic acid > phenol > water > alcohol
8 — Ethers
Williamson synthesisC₂H₅ONa + C₂H₅Br → C₂H₅–O–C₂H₅ + NaBr
Ethers are unreactive, low-boiling liquids used as solvents; diethyl ether was the first surgical anaesthetic.
9 — Exam recap
- Classify alcohols: 1°/2°/3° & mono/di/tri-hydric.
- Preparation & hydrogen bonding (high b.p., solubility).
- Reactions: Na, esterification, dehydration, oxidation ladder.
- Distinguishing tests: Lucas, K₂Cr₂O₇, iodoform.
- Phenols: acidity, FeCl₃ test, uses.
- Ethers: Williamson synthesis, properties, uses.