WEBVTT

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I think we're ready now to
tackle some more or even more

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complicated examples.

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So let's draw something
crazy here.

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So let's see, let
me draw a chain.

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Let me draw it like that.

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And so like we've done in all
of the examples, you want to

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find the longest chain.

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We could count from here.

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One, two, three, four, five,
six, seven, eight, or maybe

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it's one, two, three, four,
five, six, seven.

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No.

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Or maybe it's one, two, three,
four, five, six, seven,

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eight, nine, ten.

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That is our longest chain.

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Let me make that in green.

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So our longest chain
here is in green.

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So this decane-- sorry,
this backbone has

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ten carbons in it.

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The prefix for ten is dec-.

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It is an alkane since it has
all single bonds, so we can

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write decane for the backbone.

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And then it has a group right
here and this group consists

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of one, two carbons attached
to the backbone.

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The prefix for two carbons
is eth-, so

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this is an ethyl group.

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The -yl is because it's a group
attached to the main

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alkane chain, so we call
this ethyldecane.

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But we have to specify where the
ethyl group is attached.

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And we want to give it as low of
a number as possible, so we

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start counting on the
side closest to it.

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So it's one, two, three,
four, five, so this is

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5-ethyldecane.

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Now let's complicate this
a little bit more.

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So let me just to copy
and paste this.

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So I have pasted it there.

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And let me complicate this
molecule a little bit more.

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Let me add another ethyl
group to it.

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So let's say we have another
ethyl group over there.

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Now, what is this going to be?

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Well, the longest chain is still
going to be that thing

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in green, so it's still
going to be a decane.

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But now we have two ethyl
groups, one on the five

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carbon, one, two, three,
four, five, and then

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one on the six carbon.

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So we write here-- you might
be tempted to write

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5-ethyl-6-ethyldecane, which
really wouldn't be wrong, but

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it would just be maybe
more letters

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than you want to write.

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Instead you write
5,6-diethyldecane.

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The 5,6- tells us the two
carbons on the main backbone

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that the ethyl groups are
attached to, and the di- says

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that we have two ethanes.

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Or two ethyl groups, I should
say, not ethane groups.

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Two ethyl groups, one over here
and one right over here.

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Now, let's make it even
more complex.

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Let's take our thing and let's
make it even more complex.

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So let's copy it and let
us paste it, edit,

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paste, just like that.

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Let's paste it.

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Let me make it a little
bit lower over here.

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So the exact same thing we just
dealt with, but let's add

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one more group to it.

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Let's say it looks something
like this.

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Let's say on that five carbon--
let's say on that six

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carbon right there, I have
a group that looks

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something like this.

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What is this is going
to be called?

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And here we probably want to
break it down a little bit.

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We still have the backbone,
so it's still

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going to be a decane.

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But let's just do
it step by step.

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So we know that this right here,
this is an ethyl group.

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It's on the five carbon,
so that is a 5-ethyl.

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This is another ethyl group
on the six carbon,

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so that is a 6-ethyl.

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Now, we have this
group over here.

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So how many carbons
are on this group?

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Well, we have one, two,
three carbons on it.

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We have three carbons on it, so
we might want to just call

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it a propyl group, but
notice something.

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We are attached to the carbon,
and then it later

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branches off into two.

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It actually immediately
branches off into two.

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So we could actually call this
either sec-propyl, so this

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right here, we can either call
it sec-propyl, or because it

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is connected away from the-- I
guess it's connected directly

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to the branch the way a
propyl group works.

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You could connect it and it
immediately branches, because

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you only have three carbons.

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So just to clarify things,
it's sec- because we're

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attached to two carbons
right there.

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But sec-propyl isn't what
people normally call it.

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They normally call
it isopropyl.

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And the iso- root comes from
anything of the form.

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So if I have a group that looks
like this, this would be

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isobutyl, because we have one,
two, three, four carbons, and

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we are attached right here, so
this is where we would attach

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to the main backbone.

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If I have a group that
looks like this,

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this would be isopentyl.

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I have one, two, three,
four, five carbons.

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I'm attached away
from the branch.

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But if we go one step closer,
so we're attached just like

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this, we're attached
to the original

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group, this is isopropyl.

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One, two, three carbons.

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Let me write-- isopropyl,
isobutyl, isopentyl.

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Notice what the isos-- the isos
are like Y's, I guess is

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the best way of thinking of it,
and you're attached to the

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base of the Y.

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In this case, you're almost
attached to the base of a V,

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but, hopefully, you
get the idea.

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So the common name for this
group would be isopropyl, or

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if we wanted to use the
systematic naming, we could

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just start at one as being-- let
me do this in a good color

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--as the carbon we are attached
to, and then we only

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have two carbons right
over there.

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So if we have two carbons,
we're dealing

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with an ethyl group.

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And then you could say that
you have a methyl group

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attached to the first carbon, so
it would be 1-methylethyl.

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So this could either be called
an isopropyl group, or a

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1-methylethyl group.

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And in either case-- let me
put that in parentheses.

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In either case, it's attached
to the six carbon.

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So the prefixes are going to
be on the six carbon on our

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main-- we have a 1-methylethyl,
where the

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methyl is attached to the first
carbon on the ethyl

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chain, or we could call this a
6-isopropyl group attached to

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the six carbon.

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Now, when we decide how to write
it, how do we know--

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we're going to have to
write essentially the

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ethyl and the isopropyl.

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We're going to have to
write all of that in

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front of the decane.

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How do we decide whether
to write the eth-

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or the propyl- first?

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Well, here you just do it
in alphabetical order.

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And actually these
little prefixes

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in front don't matter.

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So you compare the P to the E.

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Eth-, E comes first in
alphabetical order, so this

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would be 5,6-diethyl.

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So even though D-- well, D comes
even before E, but you

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don't even count that prefix.

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The E is what matters.

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Diethyl, and then
we could say,

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diethyl-6-isopropyldecane.

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This is the common name:
6-isopropyldecane.

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This would be the common
name for it.

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If we want to use the systematic
name, we would

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replace the 6-isopropyl
with 6,1-methylethyl.

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So let me write that down.

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So let me just copy this part.

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So copy and paste right there.

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And then I can copy and
paste this right here.

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Copy and paste.

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So it becomes
5,6-diethyl-6-1-methylethyl.

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I know it's very confusing when
you see it, but when you

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break it down, you really
could-- you would be able to

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draw this from the structure.

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And then finally you finish
with a decane.

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So hopefully, these examples
don't confuse you too much.

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In the next few videos, we'll
do more and more examples.

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Because I think with the
nomenclature on the organic

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chemistry, the more examples
you see, the better.

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This is really core, so in the
future you don't get confused

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when people throw out
something like,

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5,6-diethyl-6-(1
-methylethyl)decane.

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