Ab initio heats of formation of medium-sized hydrocarbons. 11. The benzenoid aromatics

Ab initio calculations have been performed at the SCF level in the STO-3G, 3-21G, and 6-31G* basis sets on a variety of benzenoid and nonbenzenoid aromatic hydrocarbons, ranging from benzene to coronene. It is shown that (1) the enthalpy changes for homodesmic reactions involving only benzenoid aromatics can be computed accurately in all three bases and (2) there exist group equivalents for each basis set that enable conversion of ab initio total SCF energies to accurate heats of formation. Several examples demonstrate the extension of the method to substituted benzenes. The implications of these results concerning the correlation energies of aromatic hydrocarbons and the relationship of finite planar aromatics to the infinite graphitic sheet are discussed.