In biradical reaction

The hypothesis of dynamical control has been pursued in biradical reactions, vide infra, but the notion that temperature independence of reaction pathways is a criterion for such behavior seems inappropriate since the parent bicyclo[2.I.I]-hexene does not show such behavior despite the fact that it, having many fewer vibrational modes, should be most likely to do so. The question of whether or not the stereochemistry of the rearrangement of the parent compound is under orbital symmetry control requires that the reaction be concerted. However, the heat of formation of the parent material and the heat of formation of the methyl cyclopentene diyl suggests a BDE of less than roughly 22 kcal/mol for the non-concerted cleavage of the C1-C5 bond which is 12 kcal/mol less than that observed. However, these types of BDE estimates are invariably 8-10 kcal/mol less. So, it is unclear whether or not the reaction in the parent case is perhaps partially concerted. 

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