Study of stability and thermodynamic properties for polychlorinated dihydrophezines by density functional theory

The thermodynamic properties of 76 polychlorinated dihydrophezines (PCDPs) in the gaseous state at 298.15 K and 101.325 kPa, have been calculated using the density functional theory (the BHANDHLYP/6‐31G*) with Gaussian 03 program. Based on these data, the isodesmic reactions were designed to calculate the standard formation heat (Δ f H θ ), standard Gibbs free energy of formation (Δ f G θ ) of PCDPs in the gaseous state. The relations of these thermodynamic parameters with the number and position of chlorine substituents ( N PCS ) were discussed, and it was found that there exist good correlation between thermodynamic parameters, including heat capacity at constant volume $(C_{\rm v}^\theta )$ , entropy ( S θ ), enthalpy ( H θ ), free energy ( G θ ), Δ f H θ , Δ f G θ , and N PCS . The relative stability order of PCDP congeners was theoretically proposed based on the relative magnitude of their Δ f G θ . In addition, the values of molar heat capacity at constant pressure ( C p,m ) for PCDP congeners have been calculated.