NMR determination of the microscopic constants of diprotonated diamines in aqueous solution.

The microscopic acidity constants of the diprotonated asymmetric N-methyl-substituted ethylenediamines and N-methylpiperazine were determined by using the change of the chemical shift of the methyl protons with varying acidity. The determination was carried out at 25 degrees in aqueous solution and in an ionic medium of 1M KNO(3). The basicity of the amino-functions follows the expected sequence: secondary > primary 2 > tertiary. The influence of the substituent on the basicity of the end-group is primary > secondary 2 > tertiary.