Illustrated Glossary of Organic Chemistry

Crown ether: A series of cyclic ethers, featuring several oxygen atoms each separated by two carbon atoms. Called 'crown' ethers because their three-dimensional shape resembles a crown. Named as X-crown-Y, where X is the total number of atoms in the ring and Y is the total number of oxygen atoms. Crown ethers are notable because the exhibit selective cation binding (i.e., molecular recognition). For example, 12-crown-4 binds Li+ more strongly than K+, whereas 18-crown-6 binds K+ more strongly than Li+.






12-Crown-4
  
18-Crown-6
  
Dibenzo-18-crown-6
Some crown ethers.