NONCONCERTED COPE-REARRANGEMENT - 1,2,6,7-CYCLODECATETRAENE THERMOLYSIS

From the pressure and oxygen dependence of the trapping rate a two-step mechanism for the Cope rearrangement of the title compound is deduced, its energy profile established, and the heat of formation of the intermediate diradical 3 determined. In contrast to the meso compound the rearrangement of the rac isomer proceeds by two competing processes, a concerted and a nonconcerted pathway. The different behavior of the meso and rac compound can be correlated to the boat and chair geometry of the respective transition states.