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

Thirteen congeners of polychlorinated naphthalenes (PCN) were synthesized and studied by differential scanning calorimetry (DSC). Melting points (Tm) were obtained for all thirteen, and enthalpies of fusion (ΔHf) were obtained for nine congeners. Melting points of other PCNs, except for five, were found in literature. In addition, experimental ΔHf 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 ΔHf values with descriptors μ, S (polarizability), and L (the logarithm of the gas–hexadecane partition coefficient). The individual entropy of fusion values (ΔSf) were calculated for all 75 PCNs as ratio of ΔHf and melting point (in Kelvin).