Within the framework of the simple Hckel molecular orbital model we present a "topological" generalization of the standard Hckel-Mbius rule concerning cycles of sizes 4 and 4 n + 2. This generalization says that the number of non-bonding orbitals as well as the balance between bonding and anti-bonding orbitals is preserved under a prescribed two-site "reductive" structural transformation, which for the special case of a single cycle (annulene) reduces in essence to the conventional Hckel-Mbius rule. 1992.
