Term: Bredt's rule
https://doi.org/10.1351/goldbook.B00732

Definition:
A double bond cannot be placed with one terminus at the bridgehead of a bridged ring system unless the rings are large enough to accommodate the double bond without excessive strain. For example, while bicyclo[2.2.1]hept-1-ene is only capable of existence as a transient, its higher homologues having a double bond at the bridgehead position have been isolated: e.g. B00732.png

Related Terms:
1) bridgehead (http://doi.org/10.1351/goldbook.B00736).
2) strain (http://doi.org/10.1351/goldbook.S06037).
3) transient (http://doi.org/10.1351/goldbook.T06451).

Image: Not defined (https://goldbook.iupac.org/img/inline/B00732.png) 

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

Citation: 'Bredt's rule' 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.B00732

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