Configurational Biasing of Tertiary Amide Ionophores by Alkali Metal Chelation^1,2

Configurational analysis can be used as a probe for association constants for chelation of amides with alkali metals. Carbon-13 NMR spectroscopy indicates that tertiary amides 1, 2, and 3, each bearing a triethylene oxide substituent at nitrogen, exist as a mixture of E and Z isomers. Addition of alkali metal cation (KSCN) increases the concentration of species with the Z configuration since this configuration can chelate potassium ion. High-field 1H NMR spectra have been used to determine the chelation constants for amides 1-6 in the presence of KSCN. It has been determined that (a) the carbonyl oxygen is involved in chelation and (b) the number of ether oxygens on the substituent at nitrogen is the significant factor in the chelating ability of these ionophores.