Title: isoelectronic
Long Title: IUPAC Gold Book - isoelectronic
DOI: 10.1351/goldbook.I03276
Status: current

Definition
Two or more molecular entities are described as isoelectronic if they have the same number of valence electrons and the same structure, i.e. number and connectivity of atoms, but differ in some of the elements involved. Thus: $\ce{CO}$, $\ce{N2}$ and $\ce{NO^{+}}$ are isoelectronic. $\ce{CH2=C=O}$ and $\ce{CH2=N=N}$ are isoelectronic. $\ce{CH3COCH3}$ and $\ce{CH3N=NCH3}$ have the same number of electrons, but have different structures, hence they are not described as isoelectronic.

Related Terms
- connectivity: https://goldbook.iupac.org/terms/view/C01274
- molecular entities: https://goldbook.iupac.org/terms/view/M03986
- valence: https://goldbook.iupac.org/terms/view/V06588

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1128 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/I03276/html
- json: https://goldbook.iupac.org/terms/view/I03276/json
- xml: https://goldbook.iupac.org/terms/view/I03276/xml

Citation: Citation: 'isoelectronic' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.I03276
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Accessed: 2026-05-15T04:58:45+00:00