What does nucleophile mean?
In chemistry, a nucleophile is an electron-rich species that donates a pair of electrons to an electron-deficient center, known as an electrophile. Nucleophiles may be negatively charged, as with hydroxide or alkoxide ions, or neutral molecules that possess an available electron pair, such as water or ammonia. Their reactions with electrophiles are central to substitution, addition, and condensation reactions in organic chemistry. The strength of a nucleophile depends on factors including electron density, charge, solvent, and steric accessibility. A highly reactive nucleophile may attack a reactive center readily, whereas a weaker nucleophile may require stronger conditions or a more favorable reaction partner. The term is most often encountered in discussions of reaction mechanisms, where it identifies the species responsible for forming a new covalent bond. It also conveys the wider chemical concept of electron-pair donation, linking the term closely with the idea of a Lewis base.
nounAn electron-rich atom, molecule, or ion that donates an electron pair to an electron-deficient center, usually forming a covalent bond.
- An electron-rich species that donates an electron pair to an electrophilic center, commonly an anion or a molecule containing a nonbonding electron pair.
"The alkoxide ion acts as a strong nucleophile in the substitution reaction."
"The hydroxide ion is a powerful nucleophile in aqueous substitution reactions."
"Researchers classified the organometallic compound as a soft nucleophile because of its polarizable electron cloud."
The standard plural adds -s and is used when referring to multiple electron-pair donors.
"The two nucleophiles competed for reaction with the electrophile."
Despite its nucleus-loving name, a nucleophile does not seek the nucleus—it seeks the electron-poor part of a molecule.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of nucleophile
Nucleophile combines the element nucleo-, derived from Latin nucleus, meaning “kernel” or “nut,” with the combining form -phile, based on Greek philos, meaning “loving.” The word was developed in twentieth-century chemistry alongside the contrasting term electrophile to distinguish electron-pair donors from electron-pair acceptors. Its components reflect the original metaphorical idea of chemical affinity: one species is drawn toward and reacts with the positively or otherwise electron-deficient part of another species.
Related word forms
How nucleophile is actually used
This is specialist chemical terminology, used chiefly in organic and inorganic chemistry. It is related in meaning to Lewis base, although not every Lewis base is discussed specifically as a nucleophile in a reaction mechanism.
Easily confused with nucleophile
A nucleophile is the electron-pair-donating species itself, whereas nucleophilic is the adjective describing a reagent, process, or center that behaves like one.