Homodesmotic reactions for the assessment of stabilization energies in benzenoid and other conjugated cyclic hydrocarbons

Abstract

New homodesmotic reactions are designed that provide and alternative basis for evaluating stabilization energies of benzenoid and other conjugated cyclic hydrocarbons. As in previous cases, carbon–carbon bonds are matched in the sense of having equal numbers of C_sp²–C_sp², C_sp² C_sp², C_sp²–C_sp³, etc. bonds in reactants and products, while simultaneously the various carbon–hydrogen bonds are matched as closely as possible. By minimizing extraneous energy contributions to the reaction heat arising from changes in hybridization and C–H binding, such reactions single out those structural features resulting in stabilization. These new reactions have the advantage that experimental ΔH_f° data is currently available for the necessary reactant molecules, thus allowing an explict evaluation of the homodesmotic stablization energy to be made, which is compared to quantum theoretical calculations wherever possible.