Amines are a family of organic compounds that can be produced from ammonia. Describe the structure of an amine and explain why amines are classified as bases.

Eduqas A-Level Chemistry — 4.6 Amines · Describe and Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Methylamine, CH₃NH₂, is the simplest amine. Like ammonia, it reacts with water and with acids.

Model answer (5 marks)

An amine has a nitrogen atom bonded to one or more carbon‑containing groups (alkyl or aryl). The nitrogen also carries a lone pair of electrons. As a base, the lone pair can accept a proton (H⁺) from water or an acid. Protonation of the nitrogen gives an ammonium ion and releases OH⁻ into solution, producing an alkaline solution – the behaviour is analogous to ammonia.

Examiner tips

  • Use the exact phrase "nitrogen atom bonded to one or more carbon‑containing groups" and mention the lone pair.
  • Explain that the lone pair accepts H⁺ to form an ammonium ion, giving OH⁻ and an alkaline solution.
  • Show the link between amines and ammonia’s basicity.
  • Keep the answer concise – 5 marks only.

Common mistakes

  • Forgetting to state that the nitrogen has a lone pair.
  • Describing the structure as only C–N bonds without mentioning the lone pair.
  • Claiming that amines are acids instead of bases.

Mark scheme (5 marks)

  1. An amine contains a nitrogen atom bonded to one or more carbon-containing (hydrocarbon/alkyl) groups
  2. Amines contain a lone pair of electrons on the nitrogen atom
  3. A base is a proton acceptor / substance that accepts H⁺ ions
  4. The lone pair on nitrogen accepts a proton (H⁺) from water or an acid
  5. This produces an OH⁻ ion in water / produces an alkaline solution / the amine acts similarly to ammonia in water

Key terms in this question

amine · base

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