Enthalpy of Formation of Polycyclic Aromatic Hydrocarbons and Heterocyclic Aromatic Compounds

The standard enthalpy of formation is an important indicator of the heat involved in a chemical reaction. In this work, benchmark calculations with quasi-isodesmic type reactions have been performed on 8 different polycyclic aromatic hydrocarbons (PAHs) with 9 different methodologies. All geometry optimizations were carried out at the B2PLYP-D3, B3LYP-D3, CAM-B3LYP-D3, LC-WPBE-D3, M05-2X-D3, M06-2X-D3, WB97XD, DSDPBEP86, and PBE0DH levels in conjunction with the cc-pVTZ basis set. The DSDPBEP86-optimized isodesmic reactions yield remarkably good agreement with the experimental data for most of the compounds. For the heterocyclic aromatic compounds, quasi-isodesmic reactions are carried out successfully using the cost-effective B2PLYP-D3/cc-pVTZ and B3LYP-D3/cc-pVTZ methodologies. In the case of alkyl-substituted thiophene derivatives, quasi-isodesmic reactions and the connectivity-based hierarchy (CBH) methods have yielded enthalpies of formation close to those from experiments with B2PLYP-D3/cc-pVTZ.