On the influence of spiroconjugation and electron-withdrawing effects on the Frontier orbital energies of 5-substituted cyclopentadienes

Abstract

Ab initio calculations reveal that the influence of spiroconjugation on the HOMO of 5-substituted cyclopentadienes is weak relative to electron withdrawing effects and that both the HOMO and LUMO energy levels can be lower than in cyclopentadiene contrary to the predictions of qualitative perturbation theory. In accord with these theoretical results, the reaction of 5,5-dicyanocyclopentadiene with cyclopentadiene yields only heterodimers.