Dynamic ¹H nuclear magnetic resonance spectroscopic studies of complexes formed between substituted ammonium cations and two chiral diaza-crown ethers incorporating asymmetric carbohydrate units

Two diaza-18-crown-6 derivatives (1) and (2), incorporating methyl 4,6-O-benzylidene- and methyl 4,6-O-[(S)-phenylethylidene]-x-D-mannopyranosidic residues, have been shown, by variabletemperature high-field ¹H n.m.r. spectroscopy, to form strong anisometric 1:1 complexes with substituted ammonium cations in CD₂CI₂ solutions. Although there are a few examples of almost equally populated anisometric complexes, in most cases the major complex is associated with the β-face of the macrocyclic ring. Relevant thermodynamic data have been obtained from integration of appropriate signals in the low-temperature spectra. Approximate kinetic data have been evaluated using appropriate equations for site exchange between unequally populated sites.