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Individual Kekule valence structures of biphenylene and related hydrocarbonsare comparatively studied in respect of their total pi-electron energies andthereby relative stabilities. These structures are modeled as sets ofweakly-interacting initially-double (C=C) bonds. The relevant total energiesare represented in the form of power series, wherein the averaged resonanceparameter of initially-single (C-C) bonds underlies the expansion. Torationalize the resulting distinctions in total energies, interrelations aresought between separate members of the series, on the one hand, and presence ofdefinite substructures in the given Kekule valence structure, on the otherhand. It is shown that monocycles S_1 and S_2 correspondingly containing twoand four exocyclic methylene groups (like 3,4-dimethylene cyclobutene and[4]radialene) participate in the formation of energy corrections of therelevant Kekule valence structures along with the usual conjugated circuits ofthe 4n+2 and 4n series (R_n and Q_n, n=1,2,3...). Thus, the cycles S_1 and S_2are deductively predicted to play the role of supplementary conjugated circuitsfor biphenylene-like hydrocarbons. Moreover, the S_2- and S_1- containingstructures are shown to be the most stable ones among all Kekule valencestructures of the given hydrocarbon. Meanwhile, the lowest stability ispredicted for structures in which either the neighboring hexagonal rings areconnected by two C=C bonds or two exocyclic C=C bonds are attached to the samehexagonal ring.

Supplementary Conjugated Circuits for Biphenylene and related hydrocarbons