Evaluation of a Direct 1H NMR Method for Determining LOG K and Change in H Values for Crown Ether-Alkylammonium Cation Complexation.

摘要

A direct Hydrogen 1 NMR method for determining log K values for crown ether-ammonium cation complexations using only milligram quantities of the expensive crown has been tested and evaluated for accuracy and precision by comparing the results with those obtained using the calorimetric titration method. Log K values for interactions of non-chiral crown ether, diketopyridino-18-crown-6 (1), with 1-(1-naphthyl)ethylammonium (NapEt) perchlorate in 50%CDC13-50%CD3OD and 10%Chloroform-90% Hydroxymethane at 25 C were determined by the direct 1H NMR method. Log K values for the interactions of a chiral crown ether, dimethyldiketopyridino-18-crown-6 (2) with the (R) and (S) enantiomers of NapEt in pure CD3OD at 25.0 C were also determined by the NMR method. In Table I, the results are compared with those determined by a calorimetric method. The log K values determined by the two methods are in excellent agreement. This agreement suggests that reliable complexation data can be obtained in a variety of polar and non-polar solvents by the NMR method using only milligram quantities of the hard to obtain macrocyclic ligands. (AW)