Term: conjugated system (conjugation)
https://doi.org/10.1351/goldbook.C01267

Definition:
In the original meaning a conjugated system is a molecular entity whose structure may be represented as a system of alternating single and multiple bonds: e.g. CH2=CH–CH=CH2, CH2=CH–C≡N. In such systems, conjugation is the interaction of one p-orbital with another across an intervening σ-bond in such structures. (In appropriate molecular entities d-orbitals may be involved.) The term is also extended to the analogous interaction involving a p-orbital containing an unshared electron pair, e.g. :Cl–CH=CH2.

Related Terms:
1) delocalization (http://doi.org/10.1351/goldbook.D01583).
2) homoconjugation (http://doi.org/10.1351/goldbook.H02842).
3) resonance (http://doi.org/10.1351/goldbook.R05326).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1099 (https://doi.org/10.1351/pac199466051077)

Citation: 'conjugated system (conjugation)' 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.C01267

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