THE ENERGY WELL OF DIRADICALS .5. 1,3,5-CYCLOHEXATRIENE-1,4-DIYL AND 2,4-CYCLOHEXADIENE-1,4-DIYL

The energy profile of the Bergman rearrangement of (2)-3-hexene-1,5-diyne (4) has been established from the NO and oxygen dependance of the trapping rate of the intermediate diradical 1 which leads to a heat of formation for 1,4-didehydrobenzene (1) of Delta H-f(0) = 138.0 +/- 1.0 kcal mol(-1). By the same technique the heat of formation of 1,2,4-cyclohexatriene (2), generated by thermolysis of (Z)-1,3-hexadien-5-yne (10), gives Delta H-f(0) = 105.1 +/- 1.0 kcal mol(-1) which indicates high diradical character for 2.