Diradical wells .9. Stereochemistry of cyclopropane ring opening: The case of 1,1-difluoro-2,3-diphenylcyclopropane

From the O-2-dependence of the trapping rate of 1,1-difluoro-2,3-diphenylcyclopropane in supercritical CO2 in the temperature range 110-180 degrees C and the rates of its geometrical isomerization and racemization of the Irans-isomer, the energy profile for the geometrical isomerization is derived. Assuming that 7 is a common intermediate, the temperature dependence of the ratio of the rates of isomerization/racemization leads to a lowering of 1.2 kcal . mol(-1) for the activation energy for the disrotatory cyclization of the intermediate diradical compared to the conrotatory mode. The energy barriers associated with cyclization of the diradical amount to 2.1 and 0.9 kcal . mol(-1), respectively.