Benchmark Thermochemistry of Polycyclic Aromatic Hydrocarbons

Abstract

The DLPNO-CCSD(T1)/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.

Thermochemistry of Furan and Its Derivatives: A High-Level Ab Initio Study

“…The isodesmic-type reactions with different reference species and the same number of molecules on both sides of the equation were used in the present calculations taking into account previously obtained results for different organic molecules. − The accurate Δ f H 298 ° (g) values for small reference molecules were taken from the Active Thermochemical Tables (ATcT). , For several reference molecules ( tert -butylbenzene, tetrahydrofuran, tetrahydrofurfuryl alcohol, benzaldehyde, benzoic acid, nitromethane, nitrobenzene, 2-butanone oxime, and cyclohexanone oxime), the experimental data from the original papers were used; their accuracy was confirmed by preliminary quantum-chemical calculations. In addition to these reference species, furan and 11 of its derivatives were also used in isodesmic reactions.…”

“…In this study, the domain localized pair natural orbital coupled cluster method with improved iterative triples, DLPNO–CCSD­(T 1 ), − was used in conjunction with isodesmic-type reactions to assess the accuracy of experimental data for 43 furan derivatives. Although this method was developed fairly recently, it is now quite widely used for accurate prediction of gas-phase enthalpies of formation. ,− In our previous works, − we have shown the advantage of this method in comparison with the composite G4 method, which is especially pronounced for cyclic compounds. The purpose of this study was also to determine a set of furan compounds whose experimental gas-phase enthalpies of formation can be used as benchmark values in thermochemical calculations based on the isodesmic reaction approach.…”