According to the recently discovered PCP rule, the intensity of cyclic conjugation in the fivemembered
rings of polycyclic conjugated hydrocarbons related to acenaphthylene and fluoranthene increases
with the number of phenyl-cyclopentadienyl (PCP) fragments present in the molecule. The validity
of this regularity was first observed by studying the energy effects of cyclic conjugation in the fivemembered
rings of these systems. In order to show that the PCP rule is not an artifact of the method employed,
it is necessary to confirm its validity by other approaches. We now show that the PCP rule is in perfect agreement with calculated topological π-electron ring-currents, ostensibly an independent, quantitative, theoretical – albeit, it is here argued, likewise also graph-theoretical – measure of cyclic conjugation
in the individual rings of polycyclic π-electron systems. In addition, we show that the molecularstructure
dependency of the ring currents in acenaphthylene and fluoranthene congeners also agrees with
other, earlier-established, regularities for cyclic conjugation
