Which types of substances can act as Lewis bases?

According to the theory proposed by American chemist Gilbert N. Lewis, a Lewis base is defined as any molecule or ion that possesses an unshared pair of electrons capable of being donated to form a covalent bond with an electron acceptor, known as a Lewis acid.12

Substances that can act as Lewis bases include:

• Ammonia and its organic derivatives1
• Oxides of alkali and alkaline earth metals1
• Most atoms and molecules with negative electrical charges (anions)1
• Species capable of accepting a proton (as these possess one or more unshared electron pairs)2

In these reactions, the electron pair provided by the base constitutes the chemical bond in the resulting addition compound. This process is distinct from oxidation-reduction reactions, as it involves the sharing of an electron pair rather than the complete transfer of electrons from a reducing agent to an oxidizing agent.12