Amine
Amines are derived from ammonia (NH₃), with one, two, or three hydrogens replaced by carbon radicals — which classifies them as primary, secondary, or tertiary. They're the chemical basis of many neurotransmitters and drugs.
General formula
How to classify an amine
Count the carbon groups directly attached to nitrogen, not the total number of carbons in the molecule.
| Class | Structure | Example |
|---|---|---|
| Primary | R–NH₂ | methanamine, CH₃NH₂ |
| Secondary | R–NH–R′ | dimethylamine, (CH₃)₂NH |
| Tertiary | R–N(R′)–R″ | trimethylamine, (CH₃)₃N |
| Quaternary | R₄N⁺ | tetramethylammonium ion |
A tertiary amine still has a lone pair, but no N–H bond to donate. A quaternary ammonium salt has a formal positive charge and is not a neutral amine.
Basicity, protonation, and resonance
Nitrogen can capture a proton: R–NH₂ + H⁺ ⇌ R–NH₃⁺. When a carbonyl is directly attached to nitrogen, the function becomes an amide; resonance makes that lone pair much less available.
Naming rule
Name = main chain + suffix -amine (e.g., methanamine). In secondary/ tertiary amines, the extra radicals enter as an N- prefix (e.g., N-methylethanamine).
How to name it with IUPAC
Use this sequence to move from the structure to the systematic name:
- Choose the carbon chain attached to nitrogen as the parent.
- Use -amine and mark substituents attached to nitrogen with N-.
- CH₃CH₂NHCH₃ = N-methylethanamine: methyl is attached to N.
Examples
| Name | Formula |
|---|---|
| Methanamine | CH₃NH₂ |
| Ethanamine | C₂H₅NH₂ |
| N-methylethanamine | C₂H₅NHCH₃ |
| Benzenamine (aniline) | C₆H₅NH₂ |
Visual examples
See how the functional group appears inside the chain. Compare the drawings with the formulas in the table to practice visual recognition.
Chemical reading
An amine is a Lewis base: nitrogen lone pair accepts a proton and forms ammonium salts. Primary and secondary amines can also donate H.
Properties and applications
Amines occur in amino acids, neurotransmitters, dyes, and medicines; small amines may have strong odors.
- With HCl, R–NH₂ becomes R–NH₃⁺Cl⁻. Nitrogen directly attached to C=O indicates an amide.
- Compare polarity, chain size, and hydrogen bonding before predicting physical properties.