The complete lecture — and as you scroll, the panel on the right re-tells each idea through an everyday object you already know: a hand-sanitiser pump, rising dough, a police breathalyser, a bottle of Dettol. Read the text; the animation keeps pace.
An alcohol is the hydroxyl group (–OH) bonded to a saturated (sp³) carbon, general formula R–OH. The single most useful one in your day is ethanol, CH₃CH₂OH — the spirit in the hand-sanitiser pump that flashes cold and dry the moment it touches your skin.
| By –OH count | Example |
|---|---|
| Monohydric | ethanol, CH₃CH₂OH |
| Dihydric (glycol) | ethylene glycol — radiator antifreeze |
| Trihydric | glycerol — in soaps & moisturisers |
The oldest route is fermentation: yeast (the zymase enzyme) turns sugar into ethanol and carbon dioxide. The very same reaction does two everyday jobs at once — the CO₂ bubbles make bread dough rise, and the ethanol is what turns crushed grapes into wine.
In the lab you can also hydrate an alkene, hydrolyse an alkyl halide, or reduce a carbonyl — but every road ends at R–OH.
The –OH group is polar — the H is slightly positive, the O slightly negative — so molecules grip each other like velcro hooks. These O–H···O bridges are hydrogen bonds.
The –OH group reacts in three signature ways: with sodium it fizzes off H₂ (the test for –OH), with an acid it forms a sweet-smelling ester (perfume chemistry), and with hot conc. H₂SO₄ it loses water to give an alkene (dehydration; ease 3°>2°>1°).
Oxidising 1° and 2° alcohols turns acidified orange K₂Cr₂O₇ green. That exact colour change is the heart of an old police breathalyser: ethanol on the breath flips the crystals orange → green.
The Lucas test (conc. HCl + anhydrous ZnCl₂) tells the three classes apart by how fast a cloudy layer of insoluble alkyl chloride appears.
| Alcohol | Lucas reagent |
|---|---|
| Tertiary (3°) | cloudy immediately |
| Secondary (2°) | cloudy in ~5 min |
| Primary (1°) | no change at room temperature |
A phenol has –OH bonded directly to a benzene ring (C₆H₅OH). You meet it as carbolic acid — the antiseptic that gives Dettol its sharp, hospital smell.
When phenol loses H⁺, the phenoxide ion's charge is spread into the ring by resonance, so the conjugate base is stable and phenol parts with H⁺ readily.
An ether is R–O–R′ — an oxygen bridging two alkyl groups, e.g. diethyl ether, C₂H₅–O–C₂H₅. It is made by the Williamson synthesis: a sodium alkoxide displaces the halide from an alkyl halide.
With no O–H, ethers cannot hydrogen-bond, so they boil low and stay inert — ideal solvents. Diethyl ether, dripped onto a gauze mask, was the first surgical anaesthetic.