{"term":{"id":"08786","title":"π-conjugated system","longtitle":"IUPAC Gold Book - π-conjugated system","doi":"10.1351\/goldbook.08786","code":"08786","status":"current","definitions":[{"id":1,"text":"Molecule or a part of a molecule, of which structure may be represented as a system of alternating single and multiple bonds, in which, eventually, a multiple bond can be replaced by an atom with a pair of non-bonding electrons or an atom carrying a negative charge.","notes":{"1":"Examples of conjugated systems are conjugated polymers and molecule species whose formulas drawn in terms of the valence bond theory are as follows: ","2":"Alternating arrangement of the single and multiple bonds allows the delocalization of electrons, which stabilizes conjugated systems. The most effective stabilization show planary cyclic systems with \\(2n + 2\\) delocalized electrons (where \\(n\\) is integer), so-called aromatic systems. The last two examples above are the species where the pair non-bonding electrons (thiophene) or electrons of negatively charged atom are delocalized together with \\(\\ce{\\uppi\\mbox{-}electrons}\\) giving an aromatic system.","3":"Due to the delocalization of electrons a formula drawn in terms of the valence bond theory does not fully describe the structure of a conjugated species, which actually is a combination of two or more limiting or intermediate resonance structures that are in a dynamic equilibrium. The molecular orbital theory which directly provides extended molecular orbitals spread over all contributing atoms allows better understanding of the electronic and optical properties of a conjugated system."},"links":[{"term":"conjugated polymers","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08785"},{"term":"delocalization of electrons","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08789"},{"term":"molecular orbital theory","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08841"},{"term":"valence bond theory","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08878"}],"sources":["PAC, 2022, 94, 15. 'Glossary of terms relating to electronic, photonic and magnetic properties of polymers (IUPAC Recommendations 2021)' on page 21 (https:\/\/doi.org\/10.1515\/pac-2020-0501)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/08786\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/08786\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/08786\/plain"},"citation":"Citation: 'π-conjugated system' 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.08786","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-05-08T11:35:23+00:00"}}