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- In the last video, we named some fairly simple ethers.
- In this video, we're going to think about slightly more
- complicated ones.
- In particular, what happens if, in the process of having
- an ether, we actually have a ring as opposed
- to just a long chain?
- So you can imagine a molecule that looks
- something like this.
- You have your oxygen.
- On this side of the oxygen, you have this carbon chain
- right here.
- You have a carbon chain like this.
- But then that chain bonds back to the oxygen.
- So we have a ring here.
- It's not obvious how to name this.
- You can't just look it this side and call it methyl.
- And then that side, and call it a methyl as well.
- It's the same side.
- It connects back to itself.
- How do you name this type of ether?
- What you do is, you just number it.
- You number the longest carbon chain, like we've always done
- in the case of an alkane.
- We can start numbering here.
- 1, 2, 3, 4.
- If we just think about the carbon chain by itself.
- We know if it's one carbon, the prefix is meth-.
- Two, it's eth-.
- Three, it's prop-.
- Four, it's but-.
- So if this was just a carbon chain, we
- would call this butane.
- If we only looked at this carbon chain right here, you
- would call this butane.
- But obviously this isn't butane.
- We have this oxygen that's bonding to the 1 and 4 carbons
- of the butane.
- To make that clear, we call this-- Let me color code this
- part right here, this oxygen right there.
- It's bonded to the 1 and the 4 carbon.
- So we call this 1 comma 4.
- And this is our new word that we're going to
- learn in this video.
- 1,4-epoxybutane.
- And it doesn't just apply when the ether forms a large ring.
- It can actually form a little subset ring
- on a regular chain.
- So you could imagine something like this.
- Let me draw a chain of carbons.
- Let's say we have five carbons.
- 1, 2, 3, 4, 5, just like that.
- Let's say that between this carbon and this carbon,
- instead of having a double bond, this carbon actually
- bonds to an oxygen, which then bonds to
- this carbon over here.
- Obviously, every carbon has four bonds, the ones that
- we're not drawing, those are hydrogens.
- How do we name this?
- Well, same exact process.
- We actually start numbering the chain closer to where the
- oxygen is bonded.
- So we start numbering at this end over here.
- 1, 2, 3, 4, 5.
- So this is pentane.
- The oxygen is bonded to the 1 and the 2 carbons.
- So we call this 1,2-epoxypentane.
- 1 comma 2-epoxypentane.
- Now, in the last video, I told you that, in general, ethers
- are fairly nonreactive.
- They actually make for good solvents.
- But, what I've just drawn here is a special case of ethers
- called epoxides.
- When you just have this three atom chain right here, where
- it's two carbons and an oxygen.
- This is a special case of an ether called an epoxide.
- This is called an epoxide.
- And this, unlike most ethers, is very reactive.
- Another way you could think about it, it's very unstable.
- This is very reactive.
- Sometimes people consider these separate from ethers.
- The reason why they're very reactive, is this three member
- ring right here.
- There's a lot of strain on these bonds.
- These electrons, these bonds don't like to be that close to
- each other.
- If you actually tried to make it with an actual model set
- with molecules, you would have trouble making it bend enough
- to actually make this bond.
- So this is highly, highly, highly unstable.
- There's actually an alternate way to name epoxides.
- The alternate way, so this is a completely legitimate way.
- You could name it just like an ether with a ring.
- This is 1,2-epoxypentane.
- But the alternate way is to pretend like you had
- a double bond here.
- That instead of this oxygen here, you had a double bond.
- If you had a double bond here, this thing would be called,
- depending how you want to name it, it
- could be called 1-pentene.
- That's if there was not this oxygen here, but if there was
- a double bond here.
- 1-pentene would look like this.
- 1, 2, 3, 4, 5.
- This is the 1 carbon.
- So, 1, 2, 3, 4, 5.
- This is what 1-petene looks like.
- We've learned that many, many, many videos ago.
- Sometimes it's called pent-1-ene, depending on which
- convention.
- This is the more common one.
- We have this oxygen here, instead of this double bond.
- Instead of calling it just 1-pentene, we call it
- 1-pentene oxide.
- Just like that.
- So both of these are the names for the same exact molecule.
- This makes it clear that it's an epoxide.
- That's kind of the special ether that is more reactive.
- This is just the general way that we name any type of
- cyclic ether.
- So let's just do one more just to make the point clear.
- Let's have a cycle branching off of a cycle.
- Let's have an epoxide off of another ring.
- Just to make the point clear.
- These aren't too hard to name.
- But the first time you seen them, a little daunting.
- Let's say we have a cyclohexane ring right here.
- So this is cyclohexane.
- But let's say we have a little epoxy branching off of it,
- just like this.
- We have that going on.
- If we wanted to make it clear that this is an epoxide, we
- would essentially pretend.
- First pretend that this is just a double bond.
- If this was just a double bond, this would be
- cyclohexene.
- If this oxygen wasn't there, and instead we just had a
- double bond here.
- You actually don't have to specify the number when you
- only have one double bonded cyclohexene.
- Because it could have been anywhere, and it would have
- essentially been the same molecule.
- But since we have this oxygen here, instead of a double bond
- that's bonding to both of these carbons, we call this
- cyclohexene oxide.
- This part, right here, makes us name
- this cyclohexene oxide.
- Or if we wanted to just name this as a traditional ether,
- we would just name this cyclohexane and put the epoxy
- in front of it.
- Either of these are valid.
- Once again, you don't have to number it.
- Because you could call it, 1,2-epoxycyclohexane, if you
- made this the 1 or the 2 carbon.
- But you know it's going to be on adjacent carbons.
- And it could have really been on any of these two.
- It could have been on the 3 and the 4, and it would have
- essentially been the same molecule.
- So this actually makes it clear exactly what the
- molecular structure of the molecule is.
- So anyway, I thought you would enjoy that.
- And in the next video, I told you that
- epoxides are reactive.
- So I'll actually show you a reaction
- dealing with epoxides.