Structure/Enthalpy of Formation Relationships for Hydrocarbons Containing Benzene Rings

Abstract

Abstract Simple protocols to convert molecular mechanics (MMX/PCMODEL), semiempirical PM3, and HF ab initio energies to accurate heats of formation for hydrocarbons with benzene rings are described. The data set consists of every hydrocarbon benzene derivative with an experimentally determined ΔHfo (g), and the ΔHfo (g)'s cover a range of -140 to +410 kJ/mol. The molecular structures are comprised of numerous structural types. Hierarchical sets of molecular structure parameters are defined to describe these molecules. The independent variables include atom types (level 1), group and ring terms (level 2), nonbonded atom interactions (level 3), and the calculated MMX, PM3 or ab initio HF energies, which contribute a final level 4 parameter for rectification of the ΔHfo (g) data. The additivity, level 1-3 parameters give an excellent correlation of the experimental ΔHfo (g)'s, average error = 3.4 kJ, and maximum error = 12.1 kJ. However, the correlations are further enhanced by addition of any level 4 parame...