Enantiomeric Recognition of Organic Ammonium Salts by Chiral Dialkyl-, Dialkenyl- and Tetramethyl-Substituted Pyridino-18-Crown-6 Ligands
BRIGHAM YOUNG UNIV PROVO UT DEPT OF CHEMISTRY
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Complexation of the enantiomeric forms of various organic ammonium salts by chiral pyridino-18-crown-6 ligands 1-8 has been studied by the temperature dependent Hydrogen 1 NMR technique. At low temperatures, the peaks in the 1H NMR spectra of the complexes attributable to the hydrogen atoms on the CH2 groups attached to the pyridine rings or the methyl hydrogens in the cases of 7 and 8, 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 as reported. Table I shows the coalescence temperatures Tc and Delta GC for the dissociation of the complexes of 1-8 with various chiral organic ammonium salts. The majority of the data are for complexes of these chiral ligands with the hydrogen perchlorate salts of R- and S-alpha-1- napthylethylamine A. It is evident from these differences in the Delta GC values in Table I that these chiral ligands exhibit enantiomeric recognition for chiral-forms of various organic ammonium salts.
- Organic Chemistry