Abstract
The aromaticity, anti-aromaticity, and two new types of behaviour of pi-hydrocarbons with one or more CmHm rings attached by polyene bridges and with or without several polyene side chains are readily obtainable “on the blackboard” directly from the structural formulae using the general pictorial method recently presented. The HOMO-LUMO types, number of non-bonding MOs, and qualitative stability are also deduced. The single pi-rings fall into four homolog classes characterized by their first members C3H3, C4H4, C5H5, and C6H6 rather than the two previous Huckel 4n, 4n + 2 types. A general rule for finding the number of NBMOs for bridged combinations of such ring types is given.
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