Nucleophile Definition in Chemistry

What Is a Nucleophile?

Ammonia molecule ball and stick model
Ammonia is an example of a nitrogen nucleophile.

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A nucleophile is an atom or molecule that donates an electron pair to make a covalent bond. It is also known as a Lewis base.

Nucleophile Examples

Any ion or molecule with a free electron pair or at least one pi bond is a nucleophile. OH- is a nucleophile. It can donate a pair of electrons to the Lewis acid H+ to form H2O. The halogens, while not nucleophilic in diatomic form (e.g., I2), are nucleophiles as anions (e.g., I-). Water, hydrogen sulfide, and ammonia are all nucleophiles.


The word nucleophile comes from combining the word nucleus with the Greek word philos, which means "love." British chemist Christopher Kelk Igold introduced the terms nucleophile and electrophile in 1933. Prior to this time, the terms anioniod and cationoid were used, which were proposed by A.J. Lapworth in 1925.


  • Lapworth, A. (1925). "Replaceability of Halogen Atoms by Hydrogen Atoms." Nature. 115: 625.
  • Mayr, Herbert; Bug, Thorsten; Gotta, Matthias F; et al. (2001). "Reference Scales for the Characterization of Cationic Electrophiles and Neutral Nucleophiles." Journal of the American Chemical Society. 123 (39): 9500–12. doi:10.1021/ja010890y
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Helmenstine, Anne Marie, Ph.D. "Nucleophile Definition in Chemistry." ThoughtCo, Aug. 29, 2020, Helmenstine, Anne Marie, Ph.D. (2020, August 29). Nucleophile Definition in Chemistry. Retrieved from Helmenstine, Anne Marie, Ph.D. "Nucleophile Definition in Chemistry." ThoughtCo. (accessed January 26, 2021).