The Bond Alternation Effects for Some Quantum Chemical Quantities of the Conjugated Compound and Its Topological Reference Systems

The topological reference systems of the polycyclic conjugated systems are the hypothetical reference systems for which construction of all substructural details of the systems, except the cycles, should be taken into account. General methods to get propagators under the Hückel approximation are presented for the topological reference systems of the polycyclic conjugated molecules with same atoms and with the bond alternation. This method enables us to discuss the influences of the bond alternation on the energy stabilization and chemical reactivity of the polycyclic conjugated systems. The topological reference systems of the Hückel annulene with same atoms and with bond alternation are examined. Some quantum chemical quantities (such as the total π electron energy, the total π electron density, the bond order, the self-atom polarizability, and the frontier electron density) of the Hückel annulene and its topological reference system are obtained in general formulae.