Thermodynamic Property and Relative Stability of 76 Polybrominated Naphthalenes by Density Functional Theory

Abstract

The fully optimized calculation of naphthalene and 75 polybrominated naphthalenes (PBNs) in the ideal gas phase were carried out at the B3LYP/6-31G* level. The corresponding thermodynamic parameters, including standard enthalpy, standard Gibbs energy, standard entropy, standard heat capacity at constant volume, and standard thermal energy (i.e., the sum of zero-point energy and thermal energy corrections for molecular translation, rotation, and vibration), were calculated according to temperature correction. In addition, the dependences of some thermodynamic parameters on the number and the position of bromine substituent are discussed. With each additional bromine atom being introduced to the PBNs, the increments of standard entropy and standard heat capacity at constant volume are about 41 J·mol-1·K-1 and 17 J·mol-1·K-1, respectively, and the decrease of standard thermal energy is about 48 kJ·mol-1. By designing isodesmic reactions, the standard enthalpy of formation and the standard Gibbs energy of formation were obtained. On the basis of the magnitude of the relative standard Gibbs energy of formation, the relative stability of PBN isomers was theoretically proposed in this work. Furthermore, comparison of the standard formation enthalpies values, obtained from the B3LYP/6-31G* method as well as four semiempirical methods (AM1, MNDO-d, MNDO, and PM3), was made for PBNs.