Nomenclature of Ethers and Epoxides
In IUPAC nomenclature ethers are always named as substituents,
even when the ether is the only functional group present in the compound. To name ethers in IUPAC:
- Identify the longest chain or largest ring (R1 or R2
as the parent compound.
- Number the parent carbon skeleton to give the carbon connected to the ether Oxygen the lower possible number.
- Name the OR substituent group as "alkoxy" = alkyl -ky + oxy. Thus, methoxy is CH3O- ; ethoxy is CH3CH2O- ; propoxy is CH3CH2CH2O- , and so on.
Common Names for simple ethers are constructed by naming the alkyl groups bonded to the ether:
are cyclic three-atom ring ethers. They are the analogs of cyclopropane in which one CH2 has been replaced by Oxygen.
In IUPAC nomenclature, this ring structure has the proper name "oxirane." The oxygen atom has the number 1 position, and then other substituents are
numbered so as to arrive at the lower set of numbers.
because the numbering 2,2,3 is a lower combination than 2,3,3.
The bromine is not given preference because of its alphabetical order unless
there are two equivalent ways to number around the ring:
It may be necessary to specify the stereochemistry of groups about the ring:
Common Names for Epoxides are based upon the alkene from which
the cyclic ether is made:
the common name of the epoxide in the last example is cis -2-hexene epoxide.