Crown ethers are cyclic
chemical compounds that consist of a ring containing several
ether groups. The most common crown ethers are
oligomers of
ethylene oxide, the repeating unit being ethyleneoxy, i.e., -CH
2CH
2O-. Important members of this series are the tetramer (n = 4), the pentamer (n = 5), and the hexamer (n = 6). 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. 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. Crown ethers are much broader than the
oligomers of ethylene oxide; an important group are derived from
catechol.