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Lewis Base

Lewis base: electron pair donor; e.g., NH₃, OH⁻, F⁻, CO, R₃P
Quick Reference
Formula / NotationLewis base: electron pair donor; e.g., NH₃, OH⁻, F⁻, CO, R₃P
Also Known AsLewis base, electron donor, nucleophile (related), HSAB base, ligand

What is Lewis Base?

A species that can donate an electron pair to an acceptor (Lewis acid) to form a coordinate bond. Lewis bases are nucleophiles and include species with lone pairs of electrons. Examples include NH₃, H₂O, and halide ions. The Lewis definition encompasses all Brønsted-Lowry bases.

Formula & Notation

Lewis base: electron pair donor; e.g., NH₃, OH⁻, F⁻, CO, R₃P

Other Names / Synonyms: Lewis base, electron donor, nucleophile (related), HSAB base, ligand

Properties & Characteristics

A Lewis base is any species that donates an electron pair to a Lewis acid to form a coordinate (dative) covalent bond. Examples include: molecules with lone pairs (NH₃, H₂O, R₂O, CO), anions (F⁻, Cl⁻, OH⁻, CN⁻), and species with π electrons (alkenes, benzene in some contexts). HSAB theory classifies Lewis bases as hard (small, high EN, low polarisability) or soft (large, low EN, high polarisability).

Uses & Applications

Lewis base applications include: ligands in coordination chemistry (NH₃, EDTA, CO as Lewis bases bound to metal ions), nucleophiles in organic reactions (halide ions, hydroxide, amines as Lewis base nucleophiles), Lewis base catalysis (DMAP as Lewis base acylation catalyst), and in biochemistry (enzyme active site residues as Lewis base ligands for metal cofactors).

Safety Information

Strong Lewis bases (cyanide, CO, organophosphines) are often highly toxic. CN⁻ inhibits cytochrome c oxidase by acting as a Lewis base to iron (Lewis acid). CO binds to haemoglobin iron. Lewis base nucleophiles that are also reactive (e.g., sodium amide NaNH₂) are pyrophoric.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Lewis Base
Formula Lewis base: electron pair donor; e.g., NH₃, OH⁻, F⁻, CO, R₃P
Synonyms Lewis base, electron donor, nucleophile (related), HSAB base, ligand

Frequently Asked Questions

A species that can donate an electron pair to an acceptor (Lewis acid) to form a coordinate bond. Lewis bases are nucleophiles and include species with lone pairs of electrons. Examples include NH₃, H₂O, and halide ions. The Lewis definition encompasses all Brønsted-Lowry bases.

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