Benchmark Thermochemistry of Polycyclic Aromatic Hydrocarbons.

The DLPNO-CCSD(T)/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.

Low-temperature heat capacity and pseudorotation in 2-methyltetrahydrofuran.

The heat capacity and phase transitions of 2-methyltetrahydrofuran in the temperature range from 7 to 350 K were measured using adiabatic calorimetry. The smoothed molar thermodynamic functions in the condensed state were determined on the basis of these measurements. The thermodynamic functions of the formation were also calculated.

Enthalpy formation of fluorene: a challenging problem for theory or experiment?

The large discrepancy between the experimental enthalpy of formation of fluorene and theoretical value calculated by the G3(MP2) method was revealed more than ten years ago. Three years later, a new experimental study of this compound was undertaken to ascertain whether there is any significant error in the thermochemical data. However, after this research, the agreement between theory and experiment was improved only slightly.

Accurate prediction of norbornadiene cycle enthalpies by DLPNO-CCSD(T )/CBS method.

The DLPNO-CCSD(T )/CBS method combined with simple reactions containing small reference species leads to an improvement in the accuracy of theoretically evaluated enthalpies of formation of medium-sized polyalicyclic hydrocarbons when compared with the widely used composite approach. The efficiency of the DLPNO-CCSD(T )/CBS method is most vividly demonstrated by comparing with the results of G4 calculations for adamantane. The most important factor in choosing appropriate working reaction is the same number of species on both sides of the equation.