Term: electron-deficient molecule
https://doi.org/10.1351/goldbook.08804

Definition:
Molecule that has fewer valence electrons than required for forming normal two-center two-electron chemical bonds and thus contains multicenter chemical bonds.

Notes:
1) Binding of atoms into molecules, clusters and macroscopic bodies in electron-deficient compounds is mediated by delocalized electrons, each being shared by three or more atoms.
2) Metals are typical electron-deficient compounds in which extreme delocalization of electrons across the whole macroscopic body exists.
3) Boron, boranes, carboranes and related compounds are typical compounds with electron-deficient molecules in which boron and some other atoms are bound by multicenter two-electron bonds, such as by the two-electron three-center bond in which two electrons bind three atoms.

Related Term: delocalization of electrons (http://doi.org/10.1351/goldbook.08789).
Related Term: delocalized electrons (http://doi.org/10.1351/goldbook.08789).

Source: PAC, 2022, 94, 15. 'Glossary of terms relating to electronic, photonic and magnetic properties of polymers (IUPAC Recommendations 2021)' on page 28 (https://doi.org/10.1515/pac-2020-0501)

Citation: 'electron-deficient molecule' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08804

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