Title: cyclo-
Long Title: IUPAC Gold Book - cyclo-
DOI: 10.1351/goldbook.C01495
Status: current

Definitions
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Definition (1)
A prefix used in names to designate a ring structure, usually italicized in inorganic, but not in organic nomenclature. Examples:  

Sources
- Blue Book, p. 497 (https://www.acdlabs.com/iupac/nomenclature/)
- Red Book, 3rd ed., p. 245

Related Reference
- Blue Book Guide, p. 30 (https://doi.org/10.1351/pac199971071327)

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Definition (2)
The prefix for an elementary reaction or some part thereof indicating that the bonds undergoing primitive changes form part of a ring in the transition state of a pericyclic process.

Related Terms
- elementary reaction: https://goldbook.iupac.org/terms/view/E02035
- pericyclic: https://goldbook.iupac.org/terms/view/P04491
- transition state: https://goldbook.iupac.org/terms/view/T06468

Source
- PAC, 1989, 61, 23. 'System for symbolic representation of reaction mechanisms (Recommendations 1988)' on page 34 (https://doi.org/10.1351/pac198961010023)

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Other Outputs
- html: https://goldbook.iupac.org/terms/view/C01495/html
- json: https://goldbook.iupac.org/terms/view/C01495/json
- xml: https://goldbook.iupac.org/terms/view/C01495/xml

Citation: Citation: 'cyclo-' 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.C01495
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.
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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: 2026-06-28T04:59:16+00:00