ABSTRACT
The thermodynamic functions, including total energy(TE), enthalpy(H°), entropy(S°), free energy(G°), zero point vibrational energy(ZPE), constant volume molar heat capacity(C v°) and thermal energy correction(E th) for 76 polychlorinated naphthalenes(PCNs), were predicted by fully optimized calculation at the B3LYP/6-31G* level. The standard heat energy of formation(ΔH f°) and standard formation free energy(ΔG f°) of PCN congeners were obtained by designing isodemic reactions. In addition, the dependences of these thermodynamic parameters on the number and the position of chlorine substitution were discussed, in which the obvious increase of TE, H°, G°, ΔH f° and ΔG f° occur once chlorine substitutions are simultaneously at position 1 and 8(or position 4 and 5). And with increasing number of chlorine atoms in PCN molecule, the values of S° and C v° increase and E th and ZPE decrease. Based on the magnitude of the relative free energy(RΔG f°), the relative stability order of PCN isomers in each congener was theoretically determined. Compared with the four semiempirical methods, AMI, MINDO/3, MNDO and PM3, the magnitude of standard formation heat energy(ΔH f°) of PCNs obtained from B3LYP/6-31G* is the highest, and the differences resulted from these methods become greater with increasing number of chlorine substitutions.
