Cyclodextrin derivatives in GC separation of racemates with different volatilities. Part XIX: Thermodynamic aspects of enantioselective GC separation of some volatiles with γ-cyclodextrins 2,3-substituted with methyl and acetyl groups



The thermodynamic parameters involved in the enantiomer separation of two homologous series of γ-lactones (C6–C8 and C10–C12) and a group of structurally related monoterpenoids with a p-menthane skeleton (menthol, i-menthol, neo-menthol, neo-i-menthol, menthone, i-menthone, and 3-oxo-1,8-cineole) are determined to investigate how inverted substitution in positions 2 and 3 of the cyclodextrin ring with methyl and acetyl groups influences the enantioselectivity of 2-O-methyl-3-O-acetyl-6-O-t-hexyldimethylsilyl-γ-cyclodextrin and 2-O-acetyl-3-O-methyl-6-O-t-hexyl-dimethylsilyl-γ-cyclodextrin. The thermodynamic results show that the methyl and acyl groups, in positions 2 and 3 respectively, act complementarily to increase enantioselectivity and that the relative configuration of the stereogenic centres in the selectands influences enantiomer separation.