DFT Calculation on 76 Polybromophenazines: Their Thermodynamic Function and Stability

Abstract

The thermodynamic functions, including enthalpy (HΘ), entropy (SΘ), and Gibbs free energy (GΘ) for 76 polybromophenazines (PBPZs) in the gaseous state at 298.15 K and 101.325 kPa, have been calculated using the density functional theory (the B3LYP/6-31G*) with the Gaussian 03 program. On the basis of these data, the isodesmic reactions were designed to calculate the standard formation heat (ΔfHΘ) and standard Gibbs energy of formation (ΔfGΘ) of PBPZs. In addition, the dependences of these thermodynamic parameters on the number and positions of bromine substitutes (NPBS) were discussed. It is suggested that ΔfHΘ and ΔfGΘ of PBPZs vary greatly with the substituent positions of bromine, with the influence order being position α > position β, while the SΘ value is increased by 10 J·mol−1·K−1 by increasing each bromine atom to PBPZs. It was found that when two bromines substitute in the same aromatic ring the ΔfHΘ and ΔfGΘ increase effect is ortho > meta > para. The relative stability order of PBPZ congeners was theoretically proposed based on the relative magnitude of their ΔfGΘ. In addition, the values of molar heat capacity at constant pressure (Cp,m) for PBPZ congeners have been calculated.