Relative Basicity of Amides & Amines (Cambridge (CIE) A Level Chemistry): Revision Note

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