Title: stopper
Long Title: IUPAC Gold Book - stopper
DOI: 10.1351/goldbook.13983
Status: current

Definition
Group bulky enough to prevent dethreading of a given macrocyclic component from a threading component or its translocation to another linear section of the threading component.

Notes
1) A stopper can be positioned at the end of the whole chain: end-group stopper, or along it: internal stopper. The latter is often a part of a rotaxane constitutional repeating unit.
2) Whether a group functions as a stopper or not depends on the size of the macrocyclic component. Accordingly, when stoppers are mentioned, the macrocyclic component should also be mentioned. Examples of stoppers for \(\upbeta\)-cyclodextrin macrocyclic component are \(\ce{-CPh3}\) end-groups or \(\ce{-CPh2\bond{-}}\) groups included in constitutional repeating units: 
3) A more complex threading component may contain several linear sections due to the presence of branch points or internal large groups that prevent movement of macrocyclic components from one linear section to another.

Related Terms
- macrocyclic component: https://goldbook.iupac.org//terms/view/13965
- rotaxane constitutional repeating unit: https://goldbook.iupac.org//terms/view/13975
- threading component: https://goldbook.iupac.org//terms/view/13985

Source
- PAC, 2012, 84, 2135. 'Terminology and nomenclature for macromolecular rotaxanes and pseudorotaxanes (IUPAC Recommendations 2012)' on page 2144 (https://doi.org/10.1351/PAC-REC-11-10-15)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/13983/html
- json: https://goldbook.iupac.org/terms/view/13983/json
- xml: https://goldbook.iupac.org/terms/view/13983/xml

Citation: Citation: 'stopper' 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.13983
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Accessed: 2026-05-09T15:55:56+00:00