RESONANCE ENERGY OF DIRADICALS - 1,8-NAPH THOQUINODIMETHANE

From the racemization of 19c and the temperature and NO dependence of the trapping rate of 20b between 218 and 288 degrees C the energy prof ile for the equilibrium 19b reversible arrow 20b is derived. The singl et-triplet splitting of the diradical is 2.5 kcal . mol(-1) with the t riplet being the ground state. By comparison of the experimental react ion enthalpy with the analogous value for 25, 26 or a hypothetical mod el reaction with non-interacting radicals it is shown that the stabili zing interaction of the radicals in the singlet state of 20b is neglig ible making the stabilization of the triplet equivalent to the singlet -triplet splitting. By using literature data it is shown by an analogo us analysis that the interaction of the radicals in the bisallyl dirad ical 28 and in the triplet state of the trimethylenmethane derivative 29 is also negligible whereas in the singlet state of 29 the interacti on is strongly destabilizing.