9701 · 34.1
Primary and secondary amines
Amines contain a nitrogen atom with a lone pair of electrons, making them both basic and nucleophilic. This allows them to react with acids, halogenoalkanes, and acyl chlorides to form a variety of important products.
Need to know
What you need to know
- **Primary (1°) amines:** One alkyl/aryl group is attached to the nitrogen atom (e.g., ethylamine, CH₃CH₂NH₂). General formula RNH₂.
- **Secondary (2°) amines:** Two alkyl/aryl groups are attached to the nitrogen atom (e.g., diethylamine, (CH₃CH₂)₂NH). General formula R₂NH.
- **Tertiary (3°) amines:** Three alkyl/aryl groups are attached to the nitrogen atom (e.g., triethylamine, (CH₃CH₂)₃N). General formula R₃N.
Explanation
Amines: Nitrogen's Nucleophilic Nature
- R–NH₂ or R₂NH — lone pair on N is nucleophilic. Basicity order is typically alkyl amines > NH₃ > aryl amines due to electron-donating/withdrawing effects.
- With a halogenoalkane, the amine's lone pair attacks the δ+ carbon in a nucleophilic substitution, leading to further alkylation to form 2°/3° amines. Using excess ammonia favours the 1° amine product.
- With an acyl chloride, the amine attacks the carbonyl carbon in a nucleophilic addition-elimination reaction. This forms a stable N-substituted amide and hydrogen chloride gas.
- As bases, amines react with acids in a neutralisation reaction to form water-soluble ionic salts, called ammonium salts, such as ethylammonium chloride, RNH₃⁺Cl⁻.