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
