Extending the phenyl-cyclopentadienyl rule Abstract: By examining the energy effect of cyclic conjugation in individual rings of acenaphthylene- and fluoranthene-type polycyclic conjugated molecules, a peculiar pegularity – named the “PCP rule” – was recently discovered [Gutman I, Đurđević J & Balaban AT, Polycycl Arom Comp, 29 (2009) 3]. According to the PCP rule, a six-membered ring which is connected to the five-membered ring by a single carbon-carbon bond increases the cyclic conjugation in the five-membered ring. An analogous regularity also exist in polycyclic conjugated species possessing an odd-membered ring of size greater than five. 2009 https://phaidrabg.bg.ac.rs/o:34073 cobiss:1541785066 ISSN: 0376-4710 application/pdf 301247 bytes Keywords: Theoretcal chemistry, Graph theory, PCP rule, Energy effects, Cyclic conjugation, Polycyclic conjugation Indian Journal of Chemistry vol. 48 br. 5 str. 658-662 eng All rights reserved info:eu-repo/semantics/article Gutman, Ivan Jeremić, Svetlana Petrović, Vladimir