The semi-empirical method AM1 was used to study the reaction pathway of the thermal isomerization of a homoazulene (1, 5-methano[10] annulene). The conclusion that there is a ground-state di-π-methane radical rearrangement in the reaction pathway is obtained. The geometry, energies of each stationary point in the reaction pathway and the activation energies of each step in the reaction pathway are also calculated.

Key words: INTERMEDIATE, REARRANGEMENT REACTION, ISOMERIZATION REACTION, ACTIVATION ENERGY, ANNULENE, TRANSITION STATE, IRC, FREE RADICALS, AM1