Title: electrocyclic reaction
Long Title: IUPAC Gold Book - electrocyclic reaction
DOI: 10.1351/goldbook.E01948
Status: current

Definition
A molecular rearrangement that involves the formation of a $\ce{\upsigma\!\mbox{-}bond}$ between the termini of a fully conjugated linear $\ce{\uppi\!\mbox{-}electron}$ system (or a linear fragment of a $\ce{\uppi\!\mbox{-}electron}$ system) and a decrease by one in the number of , or the reverse of that process. For example:  The stereochemistry of such a process is termed 'conrotatory' or antarafacial if the substituents at the interacting termini of the conjugated system both rotate in the same sense, e.g.  or 'disrotatory' (or suprafacial) if one terminus rotates in a clockwise and the other in a counter-clockwise sense, e.g. 

Related Terms
- conjugated: https://goldbook.iupac.org//terms/view/C01267
- molecular rearrangement: https://goldbook.iupac.org//terms/view/M03997
- pericyclic reaction: https://goldbook.iupac.org//terms/view/P04491
- suprafacial: https://goldbook.iupac.org//terms/view/A00377

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1108 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/E01948/html
- json: https://goldbook.iupac.org/terms/view/E01948/json
- xml: https://goldbook.iupac.org/terms/view/E01948/xml

Citation: Citation: 'electrocyclic reaction' 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.E01948
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Accessed: 2026-06-07T05:00:09+00:00