Lithiation refers to the process by which a lithium atom replaces a hydrogen atom in an organic molecule. The resultant molecule is described as an organolithium compound. The C-Li bond is highly polarized, the carbon atom is electron rich, and therefore organolithium compounds are strongly basic and nucleophilic. As a result, lithiations and organolithium reactions are among the most important in organic synthesis and are useful in the synthesis of complex molecules (e.g. building C-C bonds).
Organolithium reagents are used for lithium-halogen exchange, ortho metalation and to produce other nucleophilic organometallics, such as boron reagents. Organolithium reagents are themselves produced for example, by halogen-metal exchange, lithiation of organic halides or deprotonation of alkyl or aryl molecules.