Di-ion mechanism

Mechanistically the D-A reaction is considered a concerted, pericyclic reaction with an aromatic transition state. The driving force is the formation of two new o-bonds. The endo product is the kinetic product and its formation is explained by secondary orbital interactions. Some of the mechanistic studies suggested that a diradical or a di-ion mechanism may be operational in certain cases. It was also shown that solvents and salts can influence reaction kinetics. ... 

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