Exploration of cyclopropyl radical ring opening to allyl radical by Newton trajectories: importance of valley-ridge inflection points to understand the topography

Abstract

Valley-ridge inflection points (VRI) on the potential energy surface for the ring opening of the cyclopropyl radical to allyl radical are determined using the tool of Newton trajectories (Quapp and Schmidt in Theor Chem Acc 128:47, 2011). VRIs play a role in the understanding of bifurcating reactions. The region where the bifurcation takes place is usually governed by a VRI point. For this important ring opening, the knowledge of the VRI point after the transition state was demanded some years ago (Mann and Hase in J Am Chem Soc 124:3208, 2002). Because the transition state is not symmetric, also the steepest descent from the transition state is not along a symmetry axis, and in such cases the steepest descent can fail the VRI point. That is the case here, indeed, though the pathway of the steepest descent goes near to a VRI point downhill. However, an electronic intersection seam disturbs the relations. The exploration of the notorious curvilinear potential energy surface of this ring opening has delivered some further VRI points, which are reported. They give a frame for possible ring-opening channels including the conrotatory case.