Studies of Thermodynamic Properties and Relative Stability of Polybrominated Xanthones by Density Functional Theory

The thermodynamic properties of xanthone（XTH） and 135 polybrominated xanthones（PBXTHs） in the standard state have been calculated at the B3LYP/6-31G＊ level using Gaussian 03 program.The isodesmic reactions were designed to calculate the standard enthalpy of formation（△fHθ） and standard free energy of formation（△fGθ） of PBXTH congeners.The relations of these thermodynamic parameters with the number and position of Br atom substitution（NPBS） were discussed,and it was found that there exist high correlation between thermodynamic parameters（entropy（Sθ）,△fHθ and △fGθ） and NPBS.According to the relative magnitude of their △fGθ,the relative stability order of PBXTH congeners was theoretically proposed.The relative rate constants of formation reactions of PBXTH congeners were calculated,Moreover,the values of molar heat capacity at constant pressure（Cp,m） from 200 to 1000 K for PBXTH congeners were also calculated,and the temperature dependence relation of them was obtained,suggesting very good relationships between Cp,m and temperature（T,T^1 and T^2） for almost all PBXTH congeners.

DFT Study on Some Properties of Polybrominated Phenoxathiin 10-Oxides

With the B3LYP calculation method of density functional theory（DFT）and the 6-31G＊ basis set,full optimization calculation was made for phenoxathiin10-oxide（PTO）and 135 polybromine phenoxathiin 10-oxides（PBPTOs）with the Gaussian 03 program and molar heat capacity in constant volume（CVθ）value of each molecule in the standard state was obtained.The relation between CVθ and the substitution position and number of bromine atom（NPBS）was studied,and the results indicated good correlation（R2 = 1.000）between CVθ and NPBS of PBPTO compounds.Based on the output file of Gaussian 03 program,molar heat capacity at constant pressure（Cp,m）of PBPTO compounds from 200 to 1,000 K was calculated with the statistical thermodynamics program,and the correlation equation between Cp,m and temperature（T,T-1 and T-2）was obtained with the least-squares method,and the correlation coefficient of the correlation equation（R2）was 1.000.In addition,based on the partition function of each molecule calculated by vibration analysis,the relative rate constant of formation of each molecule was calculated.

Speed of Sound and Ideal-Gas Heat Capacity at Constant Pressure for HFC-125

The gaseous speed of sound, the ideal gas heat capacity at constant pressure, and the second Virial coefficient were determined for pentafluoroethane (HFC 125). A total of 49 data points of speed of sound for gaseous HFC 125 were measured for temperatures from 273 to 313 K and pressures from 32 to 479 kPa with a cylindrical, variable path acoustic interferometer. The ideal gas heat capacity at constant pressure and the second acoustic Virial coefficient were determined over the temperature range from the speed of sound measurements and were correlated as functions of temperature. An analytical expression for the second Virial coefficient derived using the square well intermolecular potential model was compared with the data.