Pericyclic Funnels Minima

The global term pericyclic funnel will be used to refer to the funnel or funnels in the S surface that occur at the critically heterosymmetric biradicaloid geometries reached near the halfway point along the path of a thermally forbidden pericyclic reaction, and the minima in S, that are encountered along one-dimensional cuts along reaction paths that miss the conical intersections (in particular, those along high-symmetry paths, which pass 

POTENTIAL ENERGY SURFACES BARRIERS, MINIMA, AND FUNNELS 

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From Example 6.4 it can be seen that the molecule may also end up in a minimum or funnel in S, or T, that is further away from the geometry of the starting species. This then corresponds to a nonspectroscopic minimum or funnel (Figure 6.3, minimum 0 such as the pericyclic funnel of the anthracene dimerization in Figure 6.7, or even to a spectroscopic minimum of another molecule or another conformer of the same molecule (Figure 6.3, minimum i). Reactions of the latter kind can sometimes be detected by product emission (Figure 6.3, path j). (Cf. Example 6.5.)... 

According to Figure 6.17, the height of the barrier between the excimer minimum and the pericyclic funnel depends both on their depths and on the relative placement of the two excited-state surfaces S and D. The depth of the diagonally distorted pericyclic funnel is determined by the nature of the biradical its dependence on molecular structure, on the head-to-head and head-to-tail orientation of the components, and on reaction medium can be discussed using the principles outlined in Section 4.4.1. 

There may well be systems in which the excimer minimum occurs in the S2 rather than the S, surface (Figure 7.27b). The approach to the pericyclic funnel P on S, may then be barrierless, and an excimer intermediate will... 

Figure 7.27. Schematic representation of the state correlation diagram for a ground-state-forbidden pericyclic reaction with an excimer minimum E a) at geometries well before the pericyclic funnel P is reached, and b) at geometries similar to those of P. ...

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