Lewis acids and bases

Diagram of some Lewis bases (left) and acids (right)
Acids and bases
Diagrammatic representation of the dissociation of acetic acid in aqueous solution to acetate and hydronium ions.
Acid types
Base types

A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH3 is a Lewis base, because it can donate its lone pair of electrons. Trimethylborane [(CH3)3B] is a Lewis acid as it is capable of accepting a lone pair. In a Lewis adduct, the Lewis acid and base share an electron pair furnished by the Lewis base, forming a dative bond.[1] In the context of a specific chemical reaction between NH3 and Me3B, a lone pair from NH3 will form a dative bond with the empty orbital of Me3B to form an adduct NH3•BMe3. The terminology refers to the contributions of Gilbert N. Lewis.[2]

The terms nucleophile and electrophile are sometimes interchangeable with Lewis base and Lewis acid, respectively. These terms, especially their abstract noun forms nucleophilicity and electrophilicity, emphasize the kinetic aspect of reactivity, while the Lewis basicity and Lewis acidity emphasize the thermodynamic aspect of Lewis adduct formation.[3]

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Lewis acid". doi:10.1351/goldbook.L03508
  2. ^ Lewis, Gilbert Newton (1923). Valence and the Structure of Atoms and Molecules. American chemical society. Monograph series. New York, New York, U.S.A.: Chemical Catalog Company. p. 142. ISBN 9780598985408. From p. 142: "We are inclined to think of substances as possessing acid or basic properties, without having a particular solvent in mind. It seems to me that with complete generality we may say that a basic substance is one which has a lone pair of electrons which may be used to complete the stable group of another atom, and that an acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. In other words, the basic substance furnishes a pair of electrons for a chemical bond, the acid substance accepts such a pair."
  3. ^ Anslyn, Eric V. (2006). Modern physical organic chemistry. Dougherty, Dennis A., 1952-. Sausalito, CA: University Science. ISBN 1891389319. OCLC 55600610.[page needed]