THE INFLUENCE OF INTRAMOLECULAR DYNAMICS ON BRANCHING RATIOS IN THERMAL REARRANGEMENTS

1- and 2-phenylbicyclo[2.1.1]hex-2-enes-5-d undergo thermal rearrangement to give products, differing only in the location of the deuterium, in a ratio of about 9:1, but with identical activation enthalpies. Similarly, optically active trans-2-methyl-l-(trans-2-phenylethenyl)cyclopropane is found to rearrange to enantiomeric methyl-phenylcyclopentenes that are formed in a 5.9:1 ratio but with virtually identical activation enthalpies. Barring repeated coincidence, these results do not seem to be explicable within the framework of the statistical theories of unimolecular kinetics such as RRKM theory, transition state theory, and variational transition state theory. The possible influence of dynamic effects in these and other unimolecular reactions is discussed. © 1990, American Chemical Society. All rights reserved.