title: Reaction Path Bifurcation in an Electrocyclic Reaction: Ring-Opening of the Cyclopropyl Radical.
abstract: Following previous work [J. Chem. Phys. 2013, 139, 154108] on a simple model of a reaction with a post-transition state valley ridge inflection point, we study the chemically important example of the electrocyclic cyclopropyl radical ring-opening reaction using direct dynamics and a reduced dimensional potential energy surface. The overall reaction requires con- or disrotation of the methylenes, but the initial stage of the ring-opening involves substantial internal rotation of only one methylene. The reaction path bifurcation is then associated with the relative sense of rotation of the second methylene. Clear deviations of reactive trajectories from the disrotatory intrinsic reaction coordinate (IRC) for the ring-opening are observed and the dynamical mechanism is discussed. Several features observed in the model system are found to be preserved in the more complex and higher dimensional ring-opening reaction. Most notable is the sensitivity of the reaction mechanism to the shape of the potential manifested as a Newtonian kinetic isotope effect upon deuterium substitution of one of the methylene hydrogens. Dependence of the product yield on frictional dissipation representing external environmental effects is also presented. The dynamics of the post-transition state cyclopropyl radical ring-opening are discussed in detail, and the use of low dimensional models as tools to analyze complicated organic reaction mechanisms is assessed in the context of this reaction.
authors.affiliation: †Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853 United States.
authors.forename: Zeb C
authors.initials: ZC
authors.lastname: Kramer
authors.affiliation: ‡School of Chemistry, University of Cardiff, Cardiff CF10 3AT, United Kingdom.
authors.forename: Barry K
authors.initials: BK
authors.lastname: Carpenter
authors.affiliation: †Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, New York 14853 United States.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Ezra
authors.affiliation: §School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom.
authors.forename: Stephen
authors.initials: S
authors.lastname: Wiggins