INVESTIGATION INTO THE GC SEPARATION OF ENANTIOMERS ON A TRIFLUOROACETYLATED CYCLODEXTRIN .2. EFFECT OF DERIVATIZATION ON STEREOSELECTIVITYTOWARDS ALCOHOLS

Two acyl and three fluoroacyl derivatives of 32 chiral alcohols have b een chromatographed on a GC column coated with -n-pentyl-3-O-trifluoro acetyl)-gamma-cyclodextrin. Significant differences were observed betw een the stereoselectivity obtained for the derivatives and that for th e underivatized alcohols. Of the derivatives, only the fluoroacylated compounds were separated into enantiomers. Derivatization with fluoroa cyl groups reversed the elution order for at least some of the analyte s. Stereoselectivity towards simple 2- and 3-hydroxy alkanes and their fluoroacyl derivatives was highest tor those alcohols with a four-car bon chain attached to the stereogenic center. For longer-chain fluoroa cyl derivative groups stereoselectivity was higher for the 2- and 3-hy droxy alkanes. Differences in stereoselectivity towards alcohols with a methyl-branched alkane chain and their fluoroacyl derivatives was re lated to the distance between the methyl group and the hydroxyl or flu oroacyl groups. Different degrees of saturation in the carbon chain re sulted in differences in stereoselectivity. Thermodynamic data calcula ted for a number of analytes suggest that the alcohols and trifluoroac etate derivatives are interacting with the stationary phase by similar mechanisms. The stereospecific interaction appears to have a hydrogen bonding or dipole-dipole contribution and some form of steric compone nt, depending upon the shape and/or size of the solute.