Benchmark Thermochemistry of Polycyclic Aromatic Hydrocarbons.

The DLPNO-CCSD(T 1 )/CBS method in conjunction with isodesmic-type reactions was used to calculate the enthalpies of formation of 30 polycyclic aromatic hydrocarbons (PAHs). The small reference species with well-determined experimental enthalpies of formation were used in these reactions. From comparison with available experimental data and other recently published high-level quantum chemical calculations, the reference values of the standard enthalpy of formation are recommended for 13 PAHs. The difference between the calculated and experimental values for these compounds does not exceed 2 kJ/mol and their experimental data can be considered as benchmark values for use in calculation of enthalpies of formation of various large PAHs and testing the accuracy of theoretical methods. The use of isodesmic-type reactions involving reference PAHs conserves the structural features of these compounds on both sides of the reaction which leads to a better error compensation. As a result, as shown in the example of coronene, a less-expensive DLPNO-CCSD(T)/CBS method can be used in this case for accurate prediction of enthalpies of formation of large PAHs.