Evaluation of entropies of fusion of polychlorinated naphthalenes by model congeners: A DSC study

Abstract

Thirteen congeners of polychlorinated naphthalenes (PCN) were synthesized and studied by differential scanning calorimetry (DSC). Melting points ( T m) were obtained for all thirteen, and enthalpies of fusion (Δ H f) were obtained for nine congeners. Melting points of other PCNs, except for five, were found in literature. In addition, experimental Δ H f values determined by DSC were found only for 1- and 2-mono-chloronaphthalenes in the literature. The missing or uncertain values of the eight melting points and 64 enthalpies of fusion were estimated by multiple linear regressions using a set of thirteen molecular descriptors as candidates for independent variables. The stepwise model of regression (SMLR) appeared to be most effective. The perfect linearity for melting points was reached with three variables: solubility parameter (DB), ionization potential (IP) and dipole moment ( μ). Similarly, SMLR produced linear result for Δ H f values with descriptors μ, S (polarizability), and L (the logarithm of the gas–hexadecane partition coefficient). The individual entropy of fusion values (Δ S f) were calculated for all 75 PCNs as ratio of Δ H f and melting point (in Kelvin).