Conformational mobility in chemically-modified cyclodextrins

Abstract

The observation that per-2,6-O-methyl-3-O-benzoyl-α-cyclodextrin (1) displays some unusual conformational behaviour in solution has led to a detailed investigation by (dynamic) NMR spectroscopy of the equilibration process that occurs in solutions of per-2,3-O-benzoyl-α-cyclodextrin (3) and some related compounds (7-9) between conformational isomers with averaged C6 and C3 molecular symmetries in certain organic solvents such as benzene, dichloromethane, and chloroform. The solvent dependence of the conformational equilibrium is also reflected in a spread of values for the specific optical rotations for 3 from +9° in 1,1,2,2-tetrachloroethane, where there is a degenerate equilibrium between species with C3 molecular symmetry, to +92° in acetone where a species with averaged C6 symmetry is present. © 1992 Kluwer Academic Publishers.