J Math Chem

Topography of Cyclopropyl Radical Ring Opening to Allyl Radical on
the CASSCF(3,3) Surface:
Valley-Ridge Inflection Points by Newton Trajectories

Wolfgang Quapp and Josep Maria Bofill




abstract

Valley-ridge inflection points (VRI) on the potential energy surface for the
ring opening of the
cyclopropyl radical to the allyl radical are determined using the tool of
Newton trajectories (NTs) [Quapp W, Schmidt B (2011) Theor Chem Acc 128:47].
The UHF surface is treated in a former paper [Quapp W, Bofill JM,
Aguilar-Mogas A (2011) Theor Ch
This paper is the extension to the more expensive CASSCF(3,3) surface.
We compare the results on the UHF surface with the more appropriate
calculation:
there are quantitative as well as qualitative changes, of course.
But many fundamental relations are the same on both surfaces.
However, we could detect new pathways on the CASSCF(3,3) surface
which highlight the bifurcation problem of this radical.

VRIs play a role in the understanding of bifurcating reactions. The region
where the bifurcation takes place is governed by a VRI point.
Because the transition state of the ring opening is not symmetric, the
steepest descent
(SD) from the transition state is not along a symmetry axis either,
and in this case the SD usually fails a downhill VRI point.
The SD from the transition state of the ring opening goes to the disrotatory
minimum of the allyl
In contrast, we find some pathways which end at the conrotatory minimum,
and which go along so-called non steepest descent paths, at least in parts.

The region of interest (around the SP of the ring opening) is crossed by
electronic intersection
Conical intersection (CI) points on the seam can be detected by NTs.
We use the possibility to explore parts of the intersection seam of the
lower CAS surface and we
connected VRI points being the corner stones of the possible ring opening
channels in the disrota and the conrotatory case.


keywords
Valley-ridge inflection point --  Newton trajectory  -- 
reaction  bifurcation  -- ring opening of the cyclopropyl radical --
disrotatory and conrotatory case