An arrangement allowed by the laws of quantum mechanics of electrons within an atom, molecule (or system of molecules).
Source: PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1937 [Terms] [Paper]
Cite as: IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.