Theory of the PCP effect and related phenomena

Abstract

Recent studies of cyclic conjugation in the five-membered ring of acenaphthylene and fluoranthene congeners revealed some peculiar regularities, of which the so-called PCP effect attracted the greatest attention. The PCP effect is a significant increase in the magnitude of cyclic conjugation in the five-membered ring caused by the six-membered rings separated from the five-membered ring by a single carbon-carbon bond. We now present the mathematical formalism of a general theory capable of treating cyclic-conjugation phenomena of this kind, of which the PCP effect is just a special case. Namely we calculate the influence of any cycle present in a polycyclic conjugated molecule on the energy effect of cyclic conjugation of any other cycle. © 2009 Springer Science+Business Media, LLC.