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.
