Term: cheletropic reaction
https://doi.org/10.1351/goldbook.C01014

Definition:
A form of cycloaddition across the terminal atoms of a fully conjugated system with formation of two new σ-bonds to a single atom of the ('monocentric') reagent. There is formal loss of one π-bond in the substrate and an increase in coordination number of the relevant atom of the reagent. An example is the addition of sulfur dioxide to butadiene: C01014.png The reverse of this type of reaction is designated 'cheletropic elimination'.

Related Terms:
1) cycloaddition (http://doi.org/10.1351/goldbook.C01496).
2) conjugated system (http://doi.org/10.1351/goldbook.C01267).
3) coordination number (http://doi.org/10.1351/goldbook.C01331).
4) addition (http://doi.org/10.1351/goldbook.A00132).
5) reagent (http://doi.org/10.1351/goldbook.R05190).
6) elimination (http://doi.org/10.1351/goldbook.E02038).

Image: Not defined (https://goldbook.iupac.org/img/inline/C01014.png) 

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1094 (https://doi.org/10.1351/pac199466051077)

Citation: 'cheletropic reaction' 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.C01014

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