Side arm participation in lariat ether carboxylate-alkali metal cation complexes in solution

Lariat ether carboxylic acids of structure CECH2OCH2C6H4–2-CO2H with crown ether (CE) ring sizes of 12-crown-4, 15-crown-5 and 18-crown-6 are prepared and converted into alkali metal–lariat ether carboxylate complexes. Absorptions for the diastereotopic benzylic protons in the 1H NMR spectra of the complexes in CDCl3 are utilized to probe the extent of side arm interaction with the crown ether-complexed metal ion as a function of the crown ether ring size and identity of the alkali metal cation.