Complexing of polyols with cations

Polyols containing three O atoms in a suitable steric arrangement form complexes with cations in aqueous solution. Suitable steric arrangements are (i) three syn-axial oxygen atoms on a 6-membered ring, and (ii) three O atoms on three consecutive C atoms constituting a clockwise and an anti-clockwise gauche arrangement. Complex formation is detected by paper electrophoresis and by NMR spectroscopy. Complex formation with diamagnetic cations causes small downfield shifts in the NMR spectra. Paramagnetic cations cause large shifts which are interpreted as being due to diamagnetic, pseudocontact, and contact interactions. The contact effect appears to be stereospecific: it requires planarity of the resonating nucleus, the metal, and the intervening bonds.