Leah here from Leah4Sci.com. And in this video, I will show you how to name epoxides. Epoxides
are also known as oxirane and this refers to a molecule that has two carbons bound to
an oxygen forming a heterocyclic compound where hetero implies that you have a non-carbon
atom in your ring.
There are two ways to name epoxides both of which may show up in your organic chemistry
course. And so, I will show you how to use both methods. The first one is to use the
prefix epoxy when the following the IUPAC rule or my puzzle piece approach to naming.
And the second one is to use suffix oxirane at the end of your molecule.
We'll start with a standard epoxide drawing out the two carbon and oxygens in a ring.
Using my puzzle piece approach, we'll start by identifying and highlighting the parent
chain. I have two carbons in my parent chain giving me a first name of eth. I have only
single bonds giving me a last name of ane. And I have the epoxy group showing up attached
to both carbons 1 and 2 and so I get the prefix 1,2-epoxy. Putting the name together, I get
1,2-epoxyethane.
Using the oxirane method, given that there's nothing coming off of this epoxide, we can
simply call this oxirane.
Now, let's look at a substituted epoxide. For the IUPAC rules, I still identify and
highlight my parent chain. In this case, numbering so that the epoxide gets the lowest number
meaning, I start from the right. Having a total of three carbons in my parent chain
gives me a first name of prop. Having only single bonds gives me a last name of ane.
Once again, the oxygen is bound to carbons 1 and 2 giving me 1,2-epoxy. This gives me
a final name of 1,2-epoxypropane.
When using the oxirane method, I identify the entire epoxide as the parent chain and
simply call it oxirane. Since I have a methyl substituent, I simply throw the word methyl
in front of oxirane. Since I only have an option to connect methyl to one or the other
carbon, I don't have to specify which one and give it a final name of methyloxirane.
Let's look at an even more substituted example. Starting with the IUPAC system, I highlight
and identify my longest carbon chain. If I number from the left, I hit epoxide at 2.
If I number from the right, I also hit the epoxide at 2 but that methyl groups gets the
lower number. And so, I number from the right. Four carbons gives me a first name of but.
Only single bonds gives me a last name of ane. The oxygen is fused to carbons 2 and
3 giving me 2,3-epoxy and the methyl and carbon 2 gives me 2-methyl. Since E goes before M,
I have 2,3-epoxy-2-methylbutane.
Now, let's look at the same structure using the oxirane method. In this case, I have multiple
substituents so I do have to number the ring. You have a unique numbering system where oxygen
gets a number 1, number 2 is going to be the more substituted or higher priority substituted
carbon of the oxirane and then 3 is the second carbon in the ring. In this case, I have three
methyl groups, two coming off of carbon 2 and one coming off of carbon 3, that gives
me 2,2,3-trimethyl followed by the suffix oxirane.
When you have a larger molecule with an epoxide, I recommend sticking with the epoxy method.
In this case, I first identify my longest parent chain and recognize that it's the branch
going down rather than just a methyl group because I have more carbons going that way.
I start numbering from the left because that is where I give the lowest number 2 all substituents.
A total of 9 carbons gives me a first name of non. Only single bonds gives me a last
name of ane. I have chlorine on carbon 1 giving me the prefix of 1-chloro. I have an epoxide
on carbons 2 and 3 giving me 2,3-epoxy. And the methyl group on carbon 7 giving me 7-methyl.
Arranging the substituents in alphabetical order, I have C followed by E followed by
M for a final name of 1-chloro-2,3-epoxy-7-methylnonane.
When you're epoxide shows up on a ring, you treat it the same way. In this case, the parent
chain has a six carbon ring. Six gives me a first name of hex. Only single bonds gives
me a last name of ane. And the fact that it's a ring gives me cyclo. When numbering, make
sure that both carbons holding the oxygen have sequential numbers. You can choose to
go clockwise or counterclockwise. The epoxide shows up on carbons 1 and 2 giving me 1,2-epoxy.
However, since there are no other substituents, the numbers are understood and I don't have
to include them. This gives me a final name of epoxycyclohexane.
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