ISSN:
0570-0833
Keywords:
Valence isomerization
;
Bullvalene
;
Rearrangement
;
Cyclooctatetraenes
;
Homotropilidene
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Compounds which undergo fast and reversible valence-bond isomerization (i.e. which have fluctuating cyclopropyl and/or double bonds) are taken to be those in which the average life-time of the valence-bond isomers at 0 °C is of the order of 100 seconds at most, and for which the maximum activation energy of the bond migration is 20 kcal/mole. The fast, reversible bond shift can scarcely be detected by chemical means, but can be recognized by NMR spectroscopy, since the time for which a proton occupies a position with a given magnetic environment has a pronounced influence on the NMR spectrum. Some examples of molecules with fluctuating bonds are cyclooctatetraene and its derivatives, unsaturated seven- membered ring systems, homotropilidene, bridged homotropilidene systems, bullvalene, and substituted bullvalenes. The last class is particularly interesting, since here the carbon atoms are continually changing their relative positions and neighbors.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/anie.196507521
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