Dh. Hochmuth et Wa. Konig, DETERMINATION OF THE ROTATIONAL ENERGY BARRIER OF PLANAR-CHIRAL CYCLOPHANES USING DYNAMIC ENANTIOSELECTIVE GAS-CHROMATOGRAPHY AND COMPUTER-SIMULATION, Liebigs Annalen, (6), 1996, pp. 947-951
We synthesized numerous new monosubstituted dioxa[11]paracyclophanes,
which are planar-chiral atropisomers due to the hindered rotation of t
he bridge about the aromatic plane, and we were able to resolve the en
antiomers of these compounds by enantioselective gas chromatography wi
th selectively modified cyclodextrims as chiral stationary phases in p
olysiloxane solution. As a consequence of the competition between enan
tiomeric resolution and enantiomerization (interconversion) during the
gas chromatographic process, coalescence phenomena or formation of pl
ateaus between peaks of both enantiomers are observable. The combinati
on of these dynamic gas chromatographic investigations with computer s
imulation of elution profiles allows the facile and precise determinat
ion of the energy barrier of the enantiomerization reaction and the el
ucidation of the influence of substituents on the energy barrier.