Comparison of various isodesmic and homodesmotic reaction heats with values derived from published ab initio molecular orbital calculations

Abstract

Ab initio theoretical reaction heats, evaluated by using total molecular energies from ten basis sets as reported in the literature, are compared with experiment for nine acyclic C₄ hydrocarbons, seven cyclic C₃ and C₄ hydrocarbons, and five benzenoid hydrocarbons. The closeness of the agreement is examined to assess the effect of the greater matching of structural features in the homodesmotic reactions, and correlated with the type of basis set employed. Extended basis sets are essential for good agreement, other than fortuitous, if one of the reactant or product species is markedly destabilized or stabilized with repect to the rest, as is the case with the small ring structures and the benzenoid hydrocarbons, respectively.