Epoxides IUPAC system

A second method for naming epoxides in the IUPAC system is described in Section 16.1. 

Although epoxides are always considered to have their oxygen atom as part of a three-membered ring, the prefix epoxy in the IUPAC system of nomenclature can be used to denote a cyclic ether of various sizes. Thus... 

Substitutive IUPAC nomenclature names epoxides as epoxy derivatives of alkanes. According to this system, ethylene oxide becomes epoxyethane, and propylene oxide becomes 1,2-epoxypropane. The prefix epoxy- always immediately precedes the alkane ending it is not listed in alphabetical order like other substituents. 

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