Influence of the molecular surface characteristics of the diastereoisomers of a quartet molecule on their physicochemical properties:: A linear solvation free-energy study

The influence of the molecular surface characteristics on the ability of a molecule, the quartet 2,4,6-trichroro-alpha,alpha,alpha',alpha',alpha ",alpha "-hexaquis(pentachrorophenyl)mesitylene (1), to interact with the neighboring solvent molecules is studied. As physicochemical properties for this study we chose the influence of the surrounding medium on the differential chromatographic retention of two atropisomeric forms of 1, the diastereomers with C-2 and D-3 symmetries, the isomerization equilibrium between these two diastereomers, and their tumbling processes in solid or viscous amorphous matrices, as observed by ESR spectroscopy. In these studies we have employed linear solvation free energy relationships (LSER), considering as the most important solute/solvent interactions the cavitational effect, the dipolarity/polarizability, and the hydrogen-bonding ability of the solvent. In order to use such an LSER approach efficiently, a general classification of classical organic solvents in eleven different categories has been carried out. The results of this study demonstrate that the shape and roughness (fractality) of the diastereomers of quartet 1 are among their most important molecular characteristics in relation to their ability to interact with the surrounding media. These molecular parameters modify the studied properties mainly as a result of cavitational effects. In contrast, when the cavitational effects are not important, as occurs with the tumbling of the isomers inside the preformed cavities of the solvent, the unique molecular parameter that discriminates the behavior of both stereoisomers seems to be the dipolarity/polarizability. From this study we can conclude that the intrinsic surface characteristics of this molecule plays an influential role in many of its physicochemical properties.