Bredt's rule
In
The rule is named after Julius Bredt, who first discussed it in 1902[1] and codified it in 1924.[2]
Bredt's rule results from geometric strain: a double bond at a bridgehead atom
There has been an active research program to seek anti-Bredt molecules,[4] with success quantified in S, the non-bridgehead atom count. The above norbornene system has S = 5, and Fawcett originally postulated that stability required S ≥ 9 in bicyclic systems[5] and S ≥ 11 in tricyclic systems.[6] For bicyclic systems examples now indicate a limit of S ≥ 7,[3] with several such compounds having been prepared.[7] Bridgehead double bonds can be found in some natural products.[8]
Bredt's rule can predict the viability of competing
Bredt's rule may also prevent a molecule from
See also
- Double bond rule — another geometric-strain constraint on alkenes
- trans-Cyclooctene — smallest unstrained trans cycloalkene
References
- .
- .
- ^ ISBN 9780074620830.
- .
- PMID 24538877.
- ISBN 9780470638859.
- .
- PMID 25399486.
- .
- S2CID 4332059.
Further reading
- Shea, Kenneth J. (1980). "Recent developments in the synthesis, structure and chemistry of bridgehead alkenes". .