A New Method for Obtaining Isotopic Fractionation Data at Multiple Sites in Rapidly Exchanging Systems

Article abstract of DOI:10.1021/ja00295a017

A new method for rapidly and conveniently obtaining isotopic fractionation factors in dilute aqueous solutions of compounds containing rapidly exchanging OH, NH, and SH groups is described.Shifts in the positions of NMR peaks for spectroscopically observable nuclei induced by isotopic substitution are the basis of this procedure which has the unique capability of separately measuring the isotopic exchange constants simultaneously for several different groups in the same molecule.The results for a series of alcohols, amines, thiols, phenols, acids, and amides with use of 13C NMR spectroscopy are reported.Atypically low values of K_frac are observed in several cases, indicating that there are strong internal hydrogen bonds in competition with those to water, yielding conformational information.