Influence of the molecular surface characteristics of the diastereoisomersof 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 ",alp ha "-hexaquis(pentachrorophenyl)mesitylene (1), to interact with the neighb oring 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 diastereomer s with C-2 and D-3 symmetries, the isomerization equilibrium between these two diastereomers, and their tumbling processes in solid or viscous amorpho us matrices, as observed by ESR spectroscopy. In these studies we have empl oyed linear solvation free energy relationships (LSER), considering as the most important solute/solvent interactions the cavitational effect, the dip olarity/polarizability, and the hydrogen-bonding ability of the solvent. In order to use such an LSER approach efficiently, a general classification o f classical organic solvents in eleven different categories has been carrie d out. The results of this study demonstrate that the shape and roughness ( fractality) of the diastereomers of quartet 1 are among their most importan t molecular characteristics in relation to their ability to interact with t he surrounding media. These molecular parameters modify the studied propert ies mainly as a result of cavitational effects. In contrast, when the cavit ational effects are not important, as occurs with the tumbling of the isome rs inside the preformed cavities of the solvent, the unique molecular param eter that discriminates the behavior of both stereoisomers seems to be the dipolarity/polarizability. From this study we can conclude that the intrins ic surface characteristics of this molecule plays an influential role in ma ny of its physicochemical properties.