STABILIZATION IN GROUND-STATE TROPILIDINE AND TROPONE

Thermochemical and structural evidence indicates that stabilization by 1,6-electronic interaction in ground-state 1,3,5-cycloheptatriene (tr opilidine) is more important than presently thought. We believe that a stabilization energy of about 6 kcal/mol is due in significant part t o homoaromatic delocalization across the sp3 carbon. The stabilization energy of tropone is nearly twice as large as the stabilization energ y of tropilidine. Comparisons are made with the larger stabilization e nergy of benzene and with the negligible stabilization energy of cyclo octatetraene, using experimental enthalpies of formation and enthalpie s of formation calculated via homodesmic and thermoneutral reactions.