Stereoisomerism of Molecular Multipropellers. 1. Static Stereochemistry of Bis- and Tris-triaryl Systems

The static stereoisomerism of bis<i>-</i> and tris<i>-</i>triaryl systems has been analyzed by a systematic stereochemical analysis, and the resulting theoretical predictions have been experimentally confirmed by using reversed-phase HPLC and ESR and <sup>1</sup>H NMR spectroscopies with a family of seven distinct polychlorinated aromatic multipropellers. To analyze the static stereochemistry of these molecules, we have developed a specific procedure that uses a symmetry-adapted symbolic notation, allowing the theoretical prediction of both the number and symmetry of the isomers of the investigated molecules. Due to the steric hindrance introduced by the presence of bulky chlorine substituents, (all) conformational isomers can be characterized experimentally by several independent techniques confirming the theoretical stereochemical predictions. The different propeller moieties that constitute the molecule appear to be nearly independent of each other. Consequently, most of the observed isomers show comparable populations in solution at room temperature.