DIRECT DETERMINATION OF ENANTIOMERIC EXCESS OF CARBOCYCLIC ESTERS BY CHIRAL CAPILLARY GAS-CHROMATOGRAPHY

Enantiomer separations of monocyclic and bicyclic esters (methyl and ethyl esters) were carried out directly by capillary gas chromatography (GC) using a chiral gamma-cyclodextrin fused-silica capillary GC column. The direct determination of enantioselectivity of an asymmetric alkylation reaction was achieved. Larger enantiomer separations were found for the bicyclic esters (alpha = 1.038-1.079) compared to the monocyclic esters (alpha = 1.013-1.022). Molecular dimensions, derived from MM2 energy-minimized structures of a monocyclic ester and a bicyclic ester, correlate well with thermodynamic data and are consistent with more than one mechanism of enantio-differentiation.