Stopped-flow multidimensional gas chromatography: A new method for the determination of enantiomerization barriers

With the stopped-flow multidimensional gas chromatographic technique enantiomerization barriers of Delta G#(T) = 70-200 kJ/mol can easily be determined. First, the racemic mixture is separated by gas chromatography on a chiral stationary phase, then one enantiomer is transferred into a heated empty reactor column where enantiomerization is performed on-line in an achiral environment in the gas phase, and finally the enantiomerized fraction is separated in a second chiral column. The enantiomerization barrier ac (T) can be calculated from the enantiomerization time, the observed enantiomeric ratio, and the enantiomerization temperature. Moreover, by calculating Delta G#(T) at different temperatures, Delta H# and Delta S# are accessible. With this method atropisomeric polychlorinated biphenyls, a chiral allene, and a chiral aziridine were investigated. (C) 1999 John Wiley & Sons, Inc.