For example, 18-crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation, and 12-crown-4 for lithium cation.
The denticity of the polyether influences the affinity of the crown ether for various cations. The resulting cations often form salts that are soluble in nonpolar solvents, and for this reason crown ethers are useful in phase transfer catalysis. The oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of the ring is hydrophobic. Crown ethers are much broader than the oligomers of ethylene oxide an important group are derived from catechol.Ĭrown ethers strongly bind certain cations, forming complexes. The first number in a crown ether's name refers to the number of atoms in the cycle, and the second number refers to the number of those atoms that are oxygen. The term 'crown' refers to the resemblance between the structure of a crown ether bound to a cation, and a crown sitting on a person's head. Important members of this series are the tetramer ( n = 4), the pentamer ( n = 5), and the hexamer ( n = 6). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., −CH 2CH 2O−. In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups ( R−O−R’). Ring molecules with several ether (–O–) groups 18-crown-6 coordinating a potassium ion
