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-diphe nylcyclopropane in supercritical CO2 in the temperature range 110-180 degrees C and the rates of its geometrical isomerization and racemizat ion of the Irans-isomer, the energy profile for the geometrical isomer ization is derived. Assuming that 7 is a common intermediate, the temp erature dependence of the ratio of the rates of isomerization/racemiza tion leads to a lowering of 1.2 kcal . mol(-1) for the activation ener gy for the disrotatory cyclization of the intermediate diradical compa red to the conrotatory mode. The energy barriers associated with cycli zation of the diradical amount to 2.1 and 0.9 kcal . mol(-1), respecti vely.