Cyclodextrins as chiral nuclear magnetic resonance shift reagents

Abstract

Although chemical shift non-equivalence between enantiotopic groups in n.m.r. spectra has often been observed employing optically active solvents or chiral lanthanide shift reagents, or when a substrate is complexed to a chiral crown compound, such methods are normally critically dependent upon suitable substrate functionality. We now report that guest binding within the chiral cavity of β-cyclodextrin in D2O provides a method for inducing 19F n.m.r. chemical shifts between the prochiral CF3 groups of compounds 1 [1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol] and 2 [1,1,1,3,3,3-hexafluoro-2-(p-tolyl)propane], it being particularly noteworthy that the latter molecule lacks the type of functional group usually required for such chiral effects.