Amines – Complete CBSE Class 12 Chemistry Notes
Unit 9 | 6 marks | CBSE 2026–27
1. Classification and Structure
Amines are derivatives of ammonia in which one or more hydrogen atoms are replaced by organic groups. They are classified as primary, secondary or tertiary according to the number of carbon groups attached to nitrogen.
2. Basic Character
Amines act as bases because nitrogen has a lone pair that can accept a proton. Basic strength depends on electronic effects, solvation and the nature of the groups attached.
3. Preparation
Important methods include reduction of nitro compounds and reactions involving suitable halides or nitriles, as prescribed by the syllabus.
4. Chemical Reactions
- Salt formation with acids.
- Acylation of suitable amines.
- Carbylamine reaction as a test for primary amines.
- Reaction with nitrous acid, giving different products depending on the type of amine.
5. Diazonium Salts
Aromatic primary amines can form diazonium salts under cold conditions using nitrous acid generated in situ. Diazonium salts are valuable intermediates in aromatic substitution and azo-coupling chemistry.
6. Identification
| Amine | Key distinction |
|---|---|
| Primary | One carbon group on N |
| Secondary | Two carbon groups on N |
| Tertiary | Three carbon groups on N |
📝 Competency Questions
- Why can an amine accept a proton?
- Why must diazotisation of an aromatic primary amine be carried out at low temperature?
- How would you distinguish a primary amine using the carbylamine reaction?
- Why are diazonium salts useful intermediates in organic synthesis?
🎯 Board Practice
- Classify given amines as primary, secondary or tertiary.
- Explain factors affecting basic strength.
- Write preparation/reactions of diazonium salts.
- Complete conversions involving aniline and diazonium compounds.
MCQs
- Amines can act as Brønsted bases. True.
- Diazotisation of aromatic primary amines is carried out at low temperature. True.
- Tertiary amines contain one carbon group attached to nitrogen. False.
- Diazonium salts can be used as synthetic intermediates. True.
Preparation, Reactions & Basicity of Amines
Classification
Amines are classified as primary, secondary or tertiary according to the number of carbon groups attached to nitrogen. This classification affects physical properties and reactions.
2° amine: R₂NH
3° amine: R₃N
Basicity
Amines behave as bases because nitrogen has a lone pair. Basicity depends on how available that lone pair is. In aromatic amines such as aniline, resonance delocalisation affects lone-pair availability.
Diazonium Salts
Aryl diazonium salts are important intermediates for aromatic substitutions and azo-coupling reactions. Know their preparation under cold conditions and the principal transformations prescribed by the syllabus.
Reaction Map
↓
substitution / coupling → aromatic product
Identification
Understand the relevant tests and distinguish primary, secondary and tertiary amines using the prescribed reactions rather than relying only on names.
Common Mistakes
- Confusing amine basicity with nucleophilicity.
- Ignoring resonance in aniline.
- Using incorrect temperature conditions for diazotisation.
Practice
- Classify given amines.
- Compare basicity of aliphatic and aromatic amines with reasoning.
- Complete diazonium-salt conversions.
- Identify an amine from chemical observations.
Amines — Basicity & Reactions
Aromatic amines → diazonium chemistry → useful conversions
Basicity
Basicity depends on the availability of the nitrogen lone pair. Resonance, inductive effects, solvation and substitution can influence the observed basicity.
Diazotisation
Primary aromatic amines can form diazonium salts under cold conditions with nitrous acid generated in situ. Diazonium chemistry is important because the diazonium group can be replaced by several functional groups.
Coupling
Aryl diazonium salts can undergo coupling with activated aromatic compounds to form azo compounds. The colour of many azo compounds makes this chemistry particularly useful in dyes.
Worked Conversion
For an aniline-to-diazonium conversion, use sodium nitrite and a mineral acid under cold conditions. The temperature is important because diazonium salts are stable only under the appropriate conditions.
CBSE Practice
- Compare basicity of amines using electronic effects.
- Write the diazotisation reaction.
- Complete diazonium-salt conversion sequences.
- Explain azo-dye formation.
- Distinguish primary, secondary and tertiary amines using prescribed tests.