CONCERTED AND NONCONCERTED REACTION-PATH - THERMOLYSIS OF DISPIRO[2.2.2.2]DECA-4,9-DIENE

The enthalpy profile for the equilibrium 1 reversible arrow 2 reversib le arrow 3 has been determined by oxygen trapping. From the oxygen dep endence at low (0.0005-0.2 bar) and high pressure (1-180 bar) between 130 and 190 degrees C the enthalpy wells of the diradicals 3 and 2 hav e been derived (3 17.1, 2 3.7 kcal . mol(-1)). The observation of a no nconcerted path for the equilibrium 1 reversible arrow 3 is important with respect to the understanding of the controlling factor of the con certed and nonconcerted path of a reaction. The existence of a favoura ble potential energy path obviously is not of prime importance.