Crown Ethers

**Definition:** Macrocyclic polyethers with the repeating unit of (-CH2-CH2-O)n where n is greater than 2 and some oxygens may be replaced by nitrogen, sulfur or phosphorus. These compounds are useful for coordinating CATIONS. The nomenclature uses a prefix to indicate the size of the ring and a suffix for the number of heteroatoms.

**Tree numbers:** - D02.355.291.308 - D04.345.051.500 - D04.345.241.308

**Synonyms:** - Crown Ether