Comparison of the Temperature Dependent 1H NMR and Empirical Force FieldTechniques in Determining Enantiomeric Recognition of Organic Ammonium Salts by

摘要

Complexation of the (R)- and (S)- forms of alpha-(1-naphthyl)ethylammoniumperchlorate by chiral pyridino-18-crown-6 ligands 1-6 has been studied by the temperature dependent 1H NMR technique. At low temperatures, the peaks in the H NMR spectra of the complexes attributable to the hydrogen atoms on the CH2 groups attached to the pyridine rings (centered at about sigma 4.5), or the methyl hydrogens in the cases of 5 and 6, separated into two peaks of equal intensities. The low temperature peak separations were 40-140 Hz. At high temperatures, the appearance of a single peak is caused by a fast intermolecular or intramolecular face to face guest exchange. The kinetic parameters for the dissociation of these complexes were calculated reported. (jes)