The compensation effect of the partition enthalpy and the entropy, and the relationships between the molecular surface area and the enthalpy for the position isomers of chlorinated biphenyls.

Abstract

The capillary gas chromatograph column retention time under isothermal conditions was observed for 46 pentachlorobiphenyls. Relative changes of the partition enthalpy (Δ(ΔH)) and the entropy (Δ(ΔS)) were calculated from the plots of natural logarithm of the ration of capacity factor and the inverse of temperature, so called as van't Hoff plots. Although a linear relationship between Δ(ΔH) and Δ(ΔS) was observed, we judged the compensation effect was "classical type". Because the intersection points of the van't Hoff plots did not become a single point. To elucidate the dependence of Δ(ΔH) on the molecular surface area (SA), two classification parameters, the number of chlorine atoms substituted at 2, 2', 6, and 6' positions (Nor-Cl) and the number of a pair of proximitive chlorine atoms (Npx-Cl), were used. Δ(ΔH) was markedly classified on the basis on Nor-Cl, but little dependence on the SA was found. On the other hand, the classification on the basis of Npx-Cl revealed a marked linear dependence of Δ(ΔH) on SA.