Diradical wells, X - Thermochemistry of 7,7-difluoro-2,7-toluenediyl

From the oxygen and temperature dependence of the trapping rate of 7,7-difl uorobenzocyclopropene (1) in the range 180-240 degrees C, the energy profil e of the equilibrium 1 reversible arrow 2 has been obtained. From the heat of hydrogenation of 1, its heat of formation is derived (Delta H-f(0) = +3. 8 kcal . mol(-1)), as a result of which the heat of formation of the single t state of the diradical 2 is estimated as 25.7 kcal . mol(-1). Whereas the trapping experiments demonstrate unambiguously a tripler ground state for 2, only a lower limit for the singlet-triplet splitting (> 6 kcal . mol(-1) ) can be given.