Title: neighbouring group participation
Long Title: IUPAC Gold Book - neighbouring group participation
DOI: 10.1351/goldbook.N04100
Status: current

Definition
The direct interaction of the reaction centre (usually, but not necessarily, an incipient carbenium centre) with a lone pair of electrons of an atom or with the electrons of a $\ce{\upsigma\!\mbox{-}}$ or $\ce{\uppi\!\mbox{-}bond}$ contained within the parent molecule but not conjugated with the reaction centre. A distinction is sometimes made between n-, $\ce{\upsigma\!\mbox{-}}$ and $\ce{\uppi\!\mbox{-}participation}$. A rate increase due to neighbouring group participation is known as 'anchimeric assistance'. 'Synartetic acceleration' is the special case of anchimeric assistance ascribed to participation by electrons binding a substituent to a carbon atom in a $\ce{\upbeta\!\mbox{-}position}$ relative to the leaving group attached to the $\ce{\upalpha\!\mbox{-}carbon}$ atom. According to the underlying model, these electrons then provide a three-centre bond (or 'bridge') 'fastening together' (as the word 'synartetic' is intended to suggest) the $\ce{\upalpha\!\mbox{-}}$ and $\ce{\upbeta\!\mbox{-}carbon}$ atoms between which the charge is divided in the intermediate bridged ion formed (and in the transition state preceding its formation). The term synartetic acceleration is not widely used.

Related Terms
- bridge: https://dev.goldbook.iupac.org/terms/view/B00736
- bridged ion: https://dev.goldbook.iupac.org/terms/view/B00737
- carbenium centre: https://dev.goldbook.iupac.org/terms/view/C00811
- intramolecular catalysis: https://dev.goldbook.iupac.org/terms/view/I03131
- leaving group: https://dev.goldbook.iupac.org/terms/view/L03493
- multi-centre bond: https://dev.goldbook.iupac.org/terms/view/M04042
- transition state: https://dev.goldbook.iupac.org/terms/view/T06468

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1145 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://dev.goldbook.iupac.org/terms/view/N04100/html
- json: https://dev.goldbook.iupac.org/terms/view/N04100/json
- xml: https://dev.goldbook.iupac.org/terms/view/N04100/xml

Citation: Citation: 'neighbouring group participation' 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.N04100
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Accessed: 2025-11-14T20:32:43+00:00