Term: frontier orbitals
https://doi.org/10.1351/goldbook.F02533

Definition:
The Highest-energy Occupied Molecular Orbital (HOMO) (filled or partly filled) and Lowest-energy Unoccupied Molecular Orbital (LUMO) (completely or partly vacant) of a molecular entity. Examination of the mixing of frontier molecular orbitals of reacting molecular entities affords an approach to the interpretation of reaction behaviour; this constitutes a simplified perturbation molecular orbital theory of chemical behaviour.

Related Terms:
1) somo (http://doi.org/10.1351/goldbook.S05765).
2) subjacent orbital (http://doi.org/10.1351/goldbook.S06067).
3) molecular entity (http://doi.org/10.1351/goldbook.M03986).
4) molecular orbital (http://doi.org/10.1351/goldbook.M03996).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1116 (https://doi.org/10.1351/pac199466051077)

Citation: 'frontier orbitals' 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.F02533

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