Amines, Biomolecules, Polymers and Chemistry in Everyday Life
What this domain tests
Amine basicity and characteristic reactions, the structure and function of carbohydrates, proteins, enzymes, vitamins and nucleic acids, polymer classification and synthesis, and the chemistry of drugs, detergents and food additives.
Core rules
- Basicity in water: (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃ > C₆H₅NH₂. Inductive release raises basicity, but steric hindrance and poorer solvation of the conjugate acid pull the tertiary amine down; the aniline lone pair is delocalised into the ring.
- Hinsberg reagent (benzenesulphonyl chloride) distinguishes primary, secondary and tertiary amines. Carbylamine reaction (CHCl₃ + KOH) is positive only for primary amines. Hoffmann bromamide degradation removes CO to give an amine with one fewer carbon.
- Diazotisation uses NaNO₂ + HCl at 273–278 K; coupling with phenol gives an azo dye.
- Glucose is an aldohexose and a reducing sugar; sucrose is non-reducing because both anomeric carbons are involved in the glycosidic bond. Starch has α-linkages, cellulose β-linkages. Proteins are linked by peptide bonds and are denatured by heat or pH change.
- Polymers: addition (polyethene, PVC) versus condensation (nylon-6,6, terylene, bakelite); vulcanisation cross-links rubber with sulphur; biodegradable polymers reduce persistence.
Worked example
Rank CH₃NH₂, (CH₃)₂NH, (CH₃)₃N and C₆H₅NH₂ as bases in water. Dimethylamine is strongest: two methyl groups release electron density while the conjugate acid is still well solvated. Trimethylamine is weaker than methylamine because its conjugate acid is poorly solvated and the lone pair is sterically crowded. Aniline is weakest because its lone pair participates in ring resonance.
Traps that cost marks
Carbylamine is not a general amine test. Aniline does not undergo Friedel–Crafts reactions. Sucrose is non-reducing; maltose and lactose are reducing. Nylon-6,6 is a condensation polymer, not an addition polymer.