This is the molecule I know as epoxypropane:
In my neck of the woods (example), this molecule is used as one of the standard examples of small chiral molecules. The name 'epoxypropane' makes a heck of a lot of sense to me $-$ an epoxy bridge spanning a single bond of what would otherwise be propane.
It seems, however, that most everyone thinks that a better name for this is propylene oxide, from Wikipedia upwards. Now, I'm an atomic physicist, so bear with me:
- I can see how the name 'propylene oxide' fits that structure. You've taken propylene and you've oxidized it.
However, I cannot see why the name 'propylene oxide' doesn't also apply to other ways to oxidize propylene, say, sticking that oxygen over at one end or in the middle,
none of which is chiral.
Now, I imagine that IUPAC has all sorts of rules to suss these things out, so:
- why is 'propylene oxide' the preferred name for epoxypropane? and
- why is epoxypropane the only isomer encompassed by the designation 'propylene oxide'?