Molecular Structure Parameters and Predictions of Enthalpies of Formation for Catacondensed and Pericondensed Polycyclic Aromatic Hydrocarbons.

Simple procedures that combine calculated ab initio theoretical energies with empirical structural parameters to correlate experimental enthalpies of formation for polycyclic aromatic hydrocarbons are evaluated for predictive potential. The analyzed data set consists of every benzenoid PAH with an experimentally determined DeltaH(f) degrees (g), i.e., nine catacondensed and three pericondensed aromatic compounds. The tested levels of theory use optimized STO-3G, 3-21G, and 6-31G calculated HF electronic energies, and energies determined at the correlated, optimized DFT B3LYP/6-31G and single point MP2/6-31G//HF/6-31G levels. The highest precision correlations of the DeltaH(f) degrees (g) data combine computed electronic energies with three types of parametrized carbon structure descriptors and a CH parameter. The predictive accuracy of this protocol is assessed using a statistical cross-validation procedure.