CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.6.7 Relative Basicity of Amides & Amines

Relative Basicity of Amides & Amines

  • A base is a species that can donate its lone pair of electrons to form a dative covalent bond with another species
  • Amines are basic as the nitrogen atom has a lone pair of electrons which can form a dative covalent bond with an
    electron-deficient species (such as an H+ ion)
  • The basicity of the amine depends on the availability of this lone pair of electrons
    • The more readily available the lone pair of electrons is for dative covalent bonding, the stronger the base
    • The less readily available the lone pair of electrons is, the weaker the base
  • Electron-donating groups such as alkyl groups increase the electron density on the nitrogen atom causing the lone pair to become more available
  • Electron-withdrawing groups such as aromatic benzene rings, cause delocalisation of the lone pair of electrons which become less readily available
  • This is why phenylamine (which contains an electron-withdrawing benzene ring) is a weaker base than propylamine (which contains an electron-donating alkyl group)

Basicity of amides

  • Amides also contain a nitrogen atom with a lone pair of electrons
  • Again, the basicity of the amide depends on the availability of this lone pair for dative covalent bonding
  • Due to the presence of the electron-withdrawing oxygen atom in the amide group, electron density is removed from the nitrogen atom
  • The lone pair on the nitrogen atom, therefore, becomes less readily available and is not available to donate to an electron-deficient species
  • Since this electron-withdrawing oxygen is characteristic of amides and is not present in amines, amides are much weaker bases than amines

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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