I think we're ready now to tackle some more or even more
complicated examples.
So let's draw something crazy here.
So let's see, let me draw a chain.
Let me draw it like that.
And so like we've done in all of the examples, you want to
find the longest chain.
We could count from here.
One, two, three, four, five, six, seven, eight, or maybe
it's one, two, three, four, five, six, seven.
No.
Or maybe it's one, two, three, four, five, six, seven,
eight, nine, ten.
That is our longest chain.
Let me make that in green.
So our longest chain here is in green.
So this decane-- sorry, this backbone has
ten carbons in it.
The prefix for ten is dec-.
It is an alkane since it has all single bonds, so we can
write decane for the backbone.
And then it has a group right here and this group consists
of one, two carbons attached to the backbone.
The prefix for two carbons is eth-, so
this is an ethyl group.
The -yl is because it's a group attached to the main
alkane chain, so we call this ethyldecane.
But we have to specify where the ethyl group is attached.
And we want to give it as low of a number as possible, so we
start counting on the side closest to it.
So it's one, two, three, four, five, so this is
5-ethyldecane.
Now let's complicate this a little bit more.
So let me just to copy and paste this.
So I have pasted it there.
And let me complicate this molecule a little bit more.
Let me add another ethyl group to it.
So let's say we have another ethyl group over there.
Now, what is this going to be?
Well, the longest chain is still going to be that thing
in green, so it's still going to be a decane.
But now we have two ethyl groups, one on the five
carbon, one, two, three, four, five, and then
one on the six carbon.
So we write here-- you might be tempted to write
5-ethyl-6-ethyldecane, which really wouldn't be wrong, but
it would just be maybe more letters
than you want to write.
Instead you write 5,6-diethyldecane.
The 5,6- tells us the two carbons on the main backbone
that the ethyl groups are attached to, and the di- says
that we have two ethanes.
Or two ethyl groups, I should say, not ethane groups.
Two ethyl groups, one over here and one right over here.
Now, let's make it even more complex.
Let's take our thing and let's make it even more complex.
So let's copy it and let us paste it, edit,
paste, just like that.
Let's paste it.
Let me make it a little bit lower over here.
So the exact same thing we just dealt with, but let's add
one more group to it.
Let's say it looks something like this.
Let's say on that five carbon-- let's say on that six
carbon right there, I have a group that looks
something like this.
What is this is going to be called?
And here we probably want to break it down a little bit.
We still have the backbone, so it's still
going to be a decane.
But let's just do it step by step.
So we know that this right here, this is an ethyl group.
It's on the five carbon, so that is a 5-ethyl.
This is another ethyl group on the six carbon,
so that is a 6-ethyl.
Now, we have this group over here.
So how many carbons are on this group?
Well, we have one, two, three carbons on it.
We have three carbons on it, so we might want to just call
it a propyl group, but notice something.
We are attached to the carbon, and then it later
branches off into two.
It actually immediately branches off into two.
So we could actually call this either sec-propyl, so this
right here, we can either call it sec-propyl, or because it
is connected away from the-- I guess it's connected directly
to the branch the way a propyl group works.
You could connect it and it immediately branches, because
you only have three carbons.
So just to clarify things, it's sec- because we're
attached to two carbons right there.
But sec-propyl isn't what people normally call it.
They normally call it isopropyl.
And the iso- root comes from anything of the form.
So if I have a group that looks like this, this would be
isobutyl, because we have one, two, three, four carbons, and
we are attached right here, so this is where we would attach
to the main backbone.
If I have a group that looks like this,
this would be isopentyl.
I have one, two, three, four, five carbons.
I'm attached away from the branch.
But if we go one step closer, so we're attached just like
this, we're attached to the original
group, this is isopropyl.
One, two, three carbons.
Let me write-- isopropyl, isobutyl, isopentyl.
Notice what the isos-- the isos are like Y's, I guess is
the best way of thinking of it, and you're attached to the
base of the Y.
In this case, you're almost attached to the base of a V,
but, hopefully, you get the idea.
So the common name for this group would be isopropyl, or
if we wanted to use the systematic naming, we could
just start at one as being-- let me do this in a good color
--as the carbon we are attached to, and then we only
have two carbons right over there.
So if we have two carbons, we're dealing
with an ethyl group.
And then you could say that you have a methyl group
attached to the first carbon, so it would be 1-methylethyl.
So this could either be called an isopropyl group, or a
1-methylethyl group.
And in either case-- let me put that in parentheses.
In either case, it's attached to the six carbon.
So the prefixes are going to be on the six carbon on our
main-- we have a 1-methylethyl, where the
methyl is attached to the first carbon on the ethyl
chain, or we could call this a 6-isopropyl group attached to
the six carbon.
Now, when we decide how to write it, how do we know--
we're going to have to write essentially the
ethyl and the isopropyl.
We're going to have to write all of that in
front of the decane.
How do we decide whether to write the eth-
or the propyl- first?
Well, here you just do it in alphabetical order.
And actually these little prefixes
in front don't matter.
So you compare the P to the E.
Eth-, E comes first in alphabetical order, so this
would be 5,6-diethyl.
So even though D-- well, D comes even before E, but you
don't even count that prefix.
The E is what matters.
Diethyl, and then we could say,
diethyl-6-isopropyldecane.
This is the common name: 6-isopropyldecane.
This would be the common name for it.
If we want to use the systematic name, we would
replace the 6-isopropyl with 6,1-methylethyl.
So let me write that down.
So let me just copy this part.
So copy and paste right there.
And then I can copy and paste this right here.
Copy and paste.
So it becomes 5,6-diethyl-6-1-methylethyl.
I know it's very confusing when you see it, but when you
break it down, you really could-- you would be able to
draw this from the structure.
And then finally you finish with a decane.
So hopefully, these examples don't confuse you too much.
In the next few videos, we'll do more and more examples.
Because I think with the nomenclature on the organic
chemistry, the more examples you see, the better.
This is really core, so in the future you don't get confused
when people throw out something like,
5,6-diethyl-6-(1 -methylethyl)decane.