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 enantionner separation of two homologous series Of gamma-lactones (C-6-C-8 and C-10-C-12) 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-gamma-cyclodextrin and 2-O-acetyl-3-O-methyl-6-O-t-hexyl-dimethylsilyl-gamma-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.