-
-
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.
-