Cyclic ethers and epoxide naming Video Lecture

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.