nonbonding molecular orbital 

https://doi.org/10.1351/goldbook.NT07083
A molecular orbital whose occupation by electrons does not contribute (or contributes insignificantly) to the binding energy of the molecule. Generally, a nonbonding MO represents the highest occupied molecular orbital of a molecule.
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1955 [Terms] [Paper]
Citation: 'nonbonding molecular orbital' 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.NT07083 RIS BibTex EndNote
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Last revised: February 24, 2014