The ring-enlarged crown ethers, 16-and 17-crown-5 and 19-to 22-crown-6, were synthesized and their cat-ion-binding abilities were evaluated by solvent extraction of aqueous alkali metal picrates. The cation-binding abilities of less symmetrical crown ethers, 3a-e and 4a, b, were generally lower than those of the common symmetrical crown ethers 15- crown-5 (5a) and 18-crown-6 (Fib), for which the less symmetrical arrangement of the ...