126110-28-9Relevant articles and documents
Benzylic Stabilization as a Mechanistic Tool for Studying Radical Rearrangements
Venkatesan, Hariharan,Greenberg, Marc M.
, p. 1053 - 1059 (2007/10/02)
The kinetic parameters for the rearrangement of, and the relative energies of radicals involved in the equilibria of, a bicyclic cyclopropylmethyl/homoallyl system were determined.Benzylic stabilization of the cyclopropylmethyl radical facilitates characterization of all four ring opening and closing processes.Kinetically disfavored endocyclic ring opening produces the thermodynamically favored homoallyl radical (10).Cyclohexenyl radical 10 is approximately 1.7 kcal/mol lower in energy than 9.The regioselectivity of ring opening of 8 is independent of any assumptions involving trapping rate constants of radical.The regioselectivity for ring opening of 8 (k1/k2 = 30.2 at 298 K) is similar to that of bicyclohexan-1-yl (1).These experiments suggest that benzylic stabilization does not significantly perturb the position of the transition state for ring opening.Therefore, phenyl substitution of a bicyclic cyclopropylmethyl radical should be a useful tool for analyzing the effects of substituents elsewhere in the system.
The Influence of Intramolecular Dynamics on Branching Ratios in Thermal Rearrangements
Newmann-Evans, Richard H.,Simon, Reyna J.,Carpenter, B. K.
, p. 695 - 711 (2007/10/02)
1- and 2-phenylbicyclohex-2-enes-5-d undergo thermal rearrangement to give products, differing only in the location of the deuterium, in ratio of about 9:1, but with identical activation enthalphies.Similarly, opticallly active trans-2-methyl-1-(trans-2-phenylethenyl)cyclopropane is found to rearrange to enantiomeric methylphenylcyclopentenes that are formed in a 5.9:1 ratio but with virtually identicyl activation enthalphies.Barring repeated coincidence, these results do not seem to be explicable within the framework of 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.
