The complete lecture — the mechanisms come alive in the live panel as you read. Scroll down; the animation keeps pace, and you can watch a nucleophile attack a carbon from behind the leaving group.
1 — Alkyl halides: classify 1°/2°/3°
- Alkyl halide — R–X (X = F, Cl, Br, I). Class is set by how many carbons attach to the C–X carbon: 1°, 2° or 3°.
2 — Preparation
From an alcohol (best)R–OH + SOCl₂ → R–Cl + SO₂↑ + HCl↑
3 — Nucleophilic substitution: Sₙ2
One concerted stepNu⁻ + R–X → [Nu···C···X]‡ → Nu–R + X⁻
One step · inversion of configuration · rate = k[RX][Nu] · favoured by 1° halides & a strong nucleophile.
4 — Nucleophilic substitution: Sₙ1
Two stepsslow: R–X → R⁺ + X⁻ · fast: R⁺ + Nu⁻ → R–Nu
Two steps · racemisation · rate = k[RX] · favoured by 3° halides (stable carbocation).
5 — Elimination (E1/E2) & Saytzeff
- E2 — base removes a β-H while X leaves, forming an alkene. Saytzeff's rule: the more substituted alkene is the major product.
6 — Reactivity, uses & the CFC/ozone note
| Bond | Reactivity |
|---|
| R–I | most reactive |
| R–Br | ↓ |
| R–Cl / R–F | least reactive |
In the stratosphere, UV splits CFCs into Cl• radicals that destroy ozone — the ozone hole.
7 — Amines: classification
| Class | Structure |
|---|
| 1° | R–NH₂ |
| 2° | R₂NH |
| 3° | R₃N |
8 — Preparation of amines
RoutesR–X + NH₃ → R–NH₂ · R–NO₂ →[H]→ R–NH₂ · R–C≡N →[H]→ R–CH₂NH₂
9 — Basicity of amines
As a baseR–NH₂ + H⁺ → R–NH₃⁺ · strength: 2° > 1° > 3° > NH₃ > aniline
Alkyl groups are electron-donating → lone pair more available. In aniline it is delocalised into the ring → weaker base.
10 — Exam recap & distinguishing tests
- Classify R–X (1°/2°/3°); preparation routes.
- Sₙ2 (inversion) vs Sₙ1 (racemisation).
- E1/E2 elimination & Saytzeff's rule.
- Reactivity order; CFCs & ozone.
- Amines: classify, prepare, basicity.
- Carbylamine (1° only) & Hinsberg tests.