Entropic intermediates and hidden rate-limiting steps in seemingly concerted cycloadditions. Observation, prediction, and origin of an isotope effect on recrossing. Academic Article uri icon

abstract

  • An unusual intramolecular kinetic isotope effect (KIE) in the reaction of dichloroketene with cis-2-butene does not fit with a simple asynchronous cycloaddition transition state, but it can be predicted from trajectory studies on a bifurcating energy surface. The origin of the KIE is related to a high propensity for transition state recrossing in this system, with heavier masses recrossing less. The KIE can also be predicted by a statistical model that treats the cycloaddition as a stepwise mechanism, the rate-limiting second step being associated with an entropic barrier for formation of the second carbon-carbon bond. The relevance of this stepwise mechanism to other asynchronous but seemingly concerted cycloadditions is suggested by examination of organocatalytic Diels-Alder reactions.

author list (cited authors)

  • Gonzalez-James, O. M., Kwan, E. E., & Singleton, D. A

complete list of authors

  • Gonzalez-James, Ollie M||Kwan, Eugene E||Singleton, Daniel A

publication date

  • January 1, 2012 11:11 AM