¹H‐NMR study of the complex formation of alditols with multivalent cations in aqueous solution using praseodymium^(III) nitrate as shift reagent

Abstract

Abstract Complexation of ten alditols with praseodymium (III) [isosteric with calcium (II) ] as the model cation has been studied in aqueous solution by 1 H‐NMR. The paramagnetic praseodymium ion shifted the resonances downfield in a regular way and allowed the identification of all the signals and the determination of the coupling constants. The following configurational sequence of tridentate ligands (H‐COH), with respect to complex formation with Pr III has been established: xylo > threo > arabino (lyxo) > glycerol > erythro, ribo . Two major effects appear to be operative: (i) secondary hydroxyl groups show better complexation than primary hydroxyl groups; (ii) gauche butane and 1,3‐dihydroxyl repulsions introduced upon complexation cause a decrease of the complex stability. Conformational data of both the uncomplexed and the complexed state in aqueous solution have been obtained from the vicinal coupling constants.