Lewis acid

In chemistry, a Lewis acid can accept a pair of electrons and form a coordinate covalent bond, after the American chemist Gilbert Lewis. The Lewis acid and Lewis base theory is one of several acid-base reaction theories, therefore the term acid is ambiguous; it should always be clarified as being a Lewis acid (only) or a Brønsted-Lowry acid.

Related Topics:
Chemistry - Electron - Coordinate covalent bond - American - Chemist - Gilbert Lewis - Lewis base - Acid-base reaction theories - Brønsted-Lowry

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An electrophile or electron acceptor is a Lewis acid. A Lewis acid usually has a low-energy LUMO, which interacts with the HOMO of the Lewis base. Unlike a Brønsted-Lowry acid, which always transfers a hydrogen ion (H+), a Lewis acid can be any electrophile (including H+). Although all Brønsted-Lowry acids are Lewis acids, in common usage the term Lewis acid is often reserved for those Lewis acids which are not Brønsted-Lowry acids.

Related Topics:
Electrophile - LUMO - HOMO - Brønsted-Lowry acid - Hydrogen - Ion

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The reactivity of Lewis acids can be judged from the Hard-Soft Acid-Base concept. There is no universally valid description of Lewis acid strength, because Lewis acid strength depends on the specific Lewis base. Christe and Dixon{{Ref|1}} have predicted Lewis acid strength based on a computational model of gas-phase affinity for fluoride, and out of a selection of common isolable Lewis acids they found that SbF5 had the strongest fluoride affinity. Fluoride is a "hard" Lewis base; chloride and "softer" Lewis bases are very difficult to study because of limitations of the computational methods, and Lewis acidity in solution suffers from the same restriction.{{Ref|2}}

Related Topics:
Hard-Soft Acid-Base concept - Christe - Dixon - Fluoride - SbF₅ - Chloride - Solution

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Some common Lewis acids include aluminium chloride, iron(III) chloride, boron trifluoride, niobium pentachloride and ytterbium(III) triflate.

Related Topics:
Aluminium chloride - Iron(III) chloride - Boron trifluoride - Niobium pentachloride - Ytterbium(III) triflate

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