The complete lecture — the carbonyl group comes alive in the live panel as you read. Scroll down; the animation keeps pace, and you can watch a real silver mirror grow inside a test tube.
1 — The carbonyl group >C=O
- Carbonyl group >C=O — sp², planar, and polar: oxygen is δ−, carbon is δ+. Aldehyde = R–CHO, ketone = R–CO–R′.
2 — Nomenclature
| Compound | IUPAC |
|---|
| CH₃CHO | ethanal |
| CH₃COCH₃ | propanone (acetone) |
3 — Preparation
Oxidation of alcohols1° R–CH₂OH —[O]→ R–CHO · 2° R₂CHOH —[O]→ R₂C=O
4 — Nucleophilic addition
- Nucleophilic addition — Nu⁻ adds to the δ+ carbon (HCN → cyanohydrin, NaHSO₃, Grignard, alcohols → acetals). Aldehydes > ketones — less +I, less steric block.
5 — Reduction & oxidation
| Compound | Oxidation |
|---|
| aldehyde | easy → carboxylic acid |
| ketone | resists |
6 — Tollens' test (silver mirror)
Tollens'R–CHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ ⟶ R–COO⁻ + 2Ag↓ + 4NH₃ + 2H₂O
A positive result — a silver mirror — means an aldehyde. Ketones give no change. Watch the mirror grow in the panel →
7 — Fehling's / Benedict's test
Fehling'sR–CHO + 2Cu²⁺ + 5OH⁻ ⟶ R–COO⁻ + Cu₂O↓ + 3H₂O
8 — Iodoform & 2,4-DNP tests
IodoformCH₃CO– (or CH₃CH(OH)–) + I₂/NaOH ⟶ CHI₃↓ (yellow)
2,4-DNP gives an orange precipitate with all carbonyls — the test for a C=O group.
9 — Aldol condensation
Aldol of ethanal2CH₃CHO —[dil. NaOH]→ CH₃CH(OH)CH₂CHO —[heat]→ CH₃CH=CHCHO + H₂O
10 — Exam recap & uses
- The polar carbonyl >C=O; aldehyde vs ketone.
- Naming (-al / -one); preparation by oxidising alcohols.
- Nucleophilic addition; aldehydes > ketones.
- Oxidation: aldehydes easy, ketones resist.
- Tests: Tollens', Fehling's, iodoform, 2,4-DNP.
- Aldol condensation; uses — formalin, acetone.