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The study continues the previous development [MATCH, 72 (2014) 39-73] of theperturbative approach to relative stabilities of pi-electron systems ofconjugated hydrocarbons modeled as sets of weakly-interacting initially-double(C=C) bonds. Distinct isomers of acyclic hydrocarbons (polyenes) are now underfocus. The relevant total pi-electron energies (E) are expressed in the form ofpower series containing members (E_(k)) of even orders (k=0,2,4,...) withrespect to the averaged resonance parameter of initially-single (C-C) bonds.Terms to within the sixth order (k=6) inclusive are shown to be of importancefor discrimination between similar isomers. In this connection, missingexpressions for corrections E_(6) are originally derived. Conjugated paths ofvarious lengths (i.e. linear chains consisting of C=C and C-C bondsalternately) are shown to be the most important (but not the only) fragmentscontributing to stabilization of any acyclic pi-electron system. Again, newtypes of fragments (substructures) are revealed (viz. the so-called compositeconjugated paths) that contribute to destabilization of the system concerned.As a result, formation of the total energy of an acyclic pi-electron system isconcluded to be governed by an interplay between stabilizing and destabilizingfactors. Accordingly, the perturbative approach applied offers us an extensionof the concept of conjugated paths. Particular isomers containing four, fiveand six C=C bonds are considered in a detail as examples.

On Relative Stabilities of Distinct Polyenes. An Extension of the Concept of Conjugated Paths