Structure of Amines
NCERT Reference: Chapter 9 – Amines – Page 241
Quick Notes
- Amines are derived from ammonia (NH3) by replacing hydrogen atoms with alkyl or aryl groups.
- The nitrogen atom in amines is sp3 hybridised and adopts a pyramidal geometry.
- Bond angles are slightly less than tetrahedral (~108°) due to lone pair repulsion.
- Based on substitution, amines are classified as 1° (primary), 2° (secondary), or 3° (tertiary).
- Simple amines have identical groups and mixed amines have different substituents.
Full Notes
Amines are organic derivatives of ammonia in which one or more hydrogen atoms are replaced by alkyl or aryl groups.
Definition and Classification
Classification is based on the number of alkyl or aryl groups replacing hydrogen atoms in NH3:
| Type | General Formula | Example |
|---|---|---|
| Primary (1°) | R–NH2 | Methylamine (CH3NH2) |
| Secondary (2°) | R2NH or R–NHR′ |
Dimethylamine (CH3)2NH |
| Tertiary (3°) | R3N or R2NR′ | Trimethylamine (CH3)3N |
If all substituents are the same = a simple amine
If different = a mixed amine
Molecular Structure and Hybridisation
The nitrogen atom in amines is trivalent and contains a lone pair.
It undergoes sp3 hybridisation, forming three sigma bonds and one lone pair.
This gives a pyramidal shape, similar to ammonia.
The bond angle is ~108°, slightly less than tetrahedral (109.5°) due to lone pair–bond pair repulsion.
Summary
- Amines are ammonia derivatives with alkyl or aryl substitution.
- Nitrogen is sp3 hybridised giving a pyramidal geometry.
- Bond angle is slightly less than tetrahedral because of lone pair repulsion.
- Amines are classified as primary, secondary, or tertiary and may be simple or mixed.