A novel method for the determination of ionization sites in polyfunctional acids and bases by NMR relaxation rate measurements

Abstract

A method which enables one to determine the site of ionization in polyfunctional acids and bases is presented. The method is based on the changes in NMR longitudinal relaxation time (T₁) of all the nuclei potentially involved, because addition or removal of a proton from a given nuclear site will affect its T₁ in a predictable way. This approach is shown to be effective even under conditions of fast exchange of the acidic proton on a range of monofunctional models (Me₃N and MeNH₂, studied by ¹⁴N and ¹⁵N NMR spectroscopy) and some polyfunctional bases (MeCONMe₂, MeCSNMe₂, 4-aminopyridine, by ¹⁴N and ¹⁷O NMR spectroscopy).