CONFORMATIONAL MOBILITY IN CHEMICALLY-MODIFIED CYCLODEXTRINS

The observation that per-2,6-O-methyl-3-O-benzoyl-alpha-cyclodextrin ( 1) displays some unusual conformational behaviour in solution has led to a detailed investigation by (dynamic) NMR spectroscopy of the equil ibration process that occurs in solutions of per-2,3-O-benzoyl-alpha-c yclodextrin (3) and some related compounds (7-9) between conformationa l isomers with averaged C6 and C3 molecular symmetries in certain orga nic solvents such as benzene, dichloromethane, and chloroform. The sol vent dependence of the conformational equilibrium is also reflected in a spread of values for the specific optical rotations for 3 from +9-d egrees in 1,1,2,2-tetrachloroethane, where there is a degenerate equil ibrium between species with C3 molecular symmetry, to +92-degrees in a cetone where a species with averaged C6 symmetry is present.