Funnel structure, potential energy surfaces

The nature of the Cl has been a subject of research for at least three decades. Between 1966 and 1972, Zimmerman, Michl and Salem [9-14] were the first to propose, independently, that for a broad class of organic reactions the structure of the funnel could be determined by locating a cone shaped crossing of the excited and ground state (potential) energy surfaces, known as conical intersection. More recently, Yarkony [15-17] and Ruendenberg [18] identified conical intersections geometries in small molecules. 

The existence of the biradicals and the multipHcity of the surfaces on which these are formed have not been demonstrated directly however, experimental results (stereochemistry of the reaction, CIDNP [chemically induced dynamic nuclear polarization], radical trapping experiments, and quantum yield measurements) support their existence. Recently, the mechanism of 1,3-migration and oxa-di-Jt-methane reactions in terms of potential energy surface and decay funnels has been described this also supports the aforementioned mechanistic impHcations. The detailed mechanism, however, depends, in a very subtle way, on the structure of the chromophoric system and the presence of the functional groups. 

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