The Relationship Between the Heats of Formation and the Molecular Electrostatic Potentials of Polyazaarenes

In order to characterize the explosive properties of high-nitrogen, energetic compounds, the heats of formation, either in the gas or the solid state, are often used as preliminary data. Their relationship to the number of nitrogen atoms involved is usually known, so exploring it cannot furnish any new information. However, the very promising, quantitative structure property relationship (QSPR) approach utilizes the molecular surface electrostatic potential V(r). We have therefore performed calculations for 12 azines and 10 azoles by the DFT B3PW91/cc-pVTZ method, and constructed their gas phase heats of formation Δf H°(298,g) by means of the isodesmic reaction approach. The acquired gas phase heats of formation Δf H°(298,g) were correlated with the molecular surface electrostatic potentials VS,max, VS,min, and VS(ring), which were calculated by the B3LYP/6-31G(d,p)//B3PW91/cc-pVTZ method. It is shown that the VS(ring) electrostatic potential describes very precisely the structures of high-nitrogen N-heteroaromatics, with both consecutive and isolated nitrogen atoms, and their thermodynamic properties.