Stability order of isomeric benzenoid hydrocarbons and Kekulé structure count

Abstract

The commonly accepted opinion that the thermodynamic stability of isomeric benzenoid hydrocarbons (assessed by their total π-electron energy and various resonance energies) increases with increasing number of Kekulé structures is shown to be violated in numerous cases. The smallest examples of such anomalous behavior are two hexacyclic pericondensed benzenoids of formula C24H14 and several pairs of heptacyclic catacondensed benzenoids of formula C30H18.

Keywords

• total π-electron energy
• Kekulé structures
• benzenoid hydrocarbons