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Ether naming and introduction | Organic chemistry | Khan Academy - YouTube
Channel: Khan Academy
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We've already touched on ethers
in several videos.
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They've been our useful aprotic
solvent in several of
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our reactions.
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But I thought it was about time
that we actually devoted
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a video or two to ethers.
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And like all things that we've
done in organic chemistry, a
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good way to familiarize
ourselves with the molecules
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and how they look, is to
actually name them.
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So let's do a couple.
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And the first few you've
seen already.
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So let's say we have this
molecule right here.
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What I'm going to do is I'm
going to teach you two
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ways to name it.
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The common name, and that's
probably the more important
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one, especially with ethers.
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Because, as you could imagine,
that is the more common name.
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That is what people say.
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And then I'll also show
you how to name it
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using the IUPAC name.
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So let me write this down.
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IUPAC name, which is the
International Union of Pure
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and Applied Chemistry.
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And they've come up with kind
of the official naming
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protocols for all of these
organic molecules.
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This is actually the convention
that we used
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earlier when we did the alkanes
and the alkenes.
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But in the case of ethers, the
common name is more common.
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So the common name for this
molecule right here.
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You look at the two carbon
groups here.
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So let's see.
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You have this one right here.
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That is an ethyl group.
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That's an ethyl group
right there.
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You have one, two carbons.
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And then you look at the other
carbon group right over there.
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That's also an ethyl group.
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You have one, two carbons.
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So you call this-- let me just
write this down-- that is also
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an ethyl group.
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So the common name for this
is just diethyl ether.
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And the ether tells you, this
part tells you, that you have
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an oxygen in between your
two ethyl groups.
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This is the common name.
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Now the International Union of
Pure and Applied Chemistry
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official name for it.
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You kind of do something similar
to how we named other
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things before.
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You look for the
longest chain.
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Let me redraw it.
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So maybe on the left hand side
I'll do the common names.
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On the right hand side I'll
do the IUPAC names.
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So let me redraw what
the common name
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of the diethyl ether.
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You look for the
longest chain.
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In this case, there's
two longest chains.
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There's this one that has
one, two carbons.
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And then you have this one,
that has one, two carbons.
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So you can pick either one.
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I'll just pick this one as the
main chain right over there.
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It has two carbons,
no double bonds.
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It is an ethane.
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And then you say, OK, I have
this alkoxy group.
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We put the oxy at the end of it
because it has this oxygen
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right here.
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But it's the alk part of it
has two carbons, one, two.
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So we call this right here,
we call this ethoxy.
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So one other way to name this,
we have this ethoxy group
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attached to the one carbon.
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We're just going to start
numbering on this side of the
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ethane, just because that's
where the group is, attached
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to the one carbon.
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So we call this 1-ethoxyethane.
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You'll almost never see it
actually named this way, even
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though this is the
official name.
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You're much more likely to see
this as diethyl ether.
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And at least in my brain, this
resonates a lot more.
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You just say what are
the two groups.
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And you throw the
ether at end.
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You know that there's an
oxygen in between.
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Let's do a couple
more of these.
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So let's say I have this
molecule right here.
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I have this molecule
right over here.
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The common way is you look at
the two groups on either side
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of the oxygen.
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So this right here-- let me do
this in a different color--
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this group on the left
right here, we have
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one, two, three carbons.
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It's a propyl group,
but we're attached
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to that middle carbon.
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So this is an isopropyl group.
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And on the right hand
side right here, we
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just have one carbon.
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So this is right here-- I keep
using that blue-- this right
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here, this is a methyl group.
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So the common way of naming
it, you just list both of
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these groups and then
you write ether.
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And you list them in
alphabetical order.
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I comes before m.
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So this is, the common name
is isopropyl methyl ether.
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Now if we were to do the IUPAC
naming, we look for the
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longest carbon chain.
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Let me redraw the
molecule itself.
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So let me redraw the same
thing right there.
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So what's the longest
carbon chain here?
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Well we have one, two, three
carbons right there.
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We only have one carbon
right there.
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So this thing right here is
our longest carbon chain.
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It has three carbons on it, and
it had no double bonds.
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So eth, meth, prop, propyl,
or it's actually propane.
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So this is our longest. So we
write propane right there,
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because we're using the IUPAC
naming mechanism.
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And then we look at this methoxy
group right here.
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And I call this a methoxy group,
because I have the o.
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That gives us the oxy.
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And I just have a methyl
group right here.
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So this is methoxy.
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You remember that meth is the
prefix for just having only
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one carbon.
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We add the oxy because
that oxygen is there.
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And it's attached to the two
carbons on the propane chain,
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no matter what direction you
start naming from, or
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numbering from.
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One, two, three.
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So this is 2-methoxypropane.
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Let's do another one.
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Let's do one more.
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And I think you'll get the
gist of at least the
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reasonably simple
ethers to name.
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So let's put a ring
over there.
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And then that's attached
to an oxygen.
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And then we have another carbon
chain right here.
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And then we have another carbon
chain right there.
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Let me just copy and paste
that so that I don't
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have to redraw it.
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So let me copy and paste.
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All right.
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So let's do the common name
first. That always tends to be
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a little bit more fun.
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So on this side, we have one,
two, three, four, five, six
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carbons in a cycle.
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This right here on the
left hand side is
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a cyclohexyl group.
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This on the right hand side,
we have one, two, three.
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This is just a straight-up
propyl group.
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And so when you name the ether,
you just put these two
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groups in alphabetical
order, and you add an
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ether at the end.
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So it's cyclohexyl.
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C comes before p.
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So it's cyclohexyl propyl.
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Let me get that shade
of yellow right.
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Cyclohexyl propyl ether.
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Now let's do the IUPAC
way to name it.
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So you look for the longest
carbon chain here.
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In this case, it's going to be
the cyclohexane right here.
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We have one, two, three, four,
five, six carbons there.
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We only have one, two,
three there.
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So this is kind of
our backbone.
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So we write down cyclohexane.
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No double bonds, so
it's a hexane.
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So that's the cyclohexane
right there.
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If you just had these three
carbons, it would be a propyl.
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But this is not just
three carbons.
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It's three carbons and
then an oxygen.
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So we would call it a propoxy.
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So this is propoxy group.
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And you don't have to number
it because it can just be
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attached to any of
these carbons.
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It would essentially be
the same molecule.
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So you can just call this
propoxy cyclohexane.
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Let me make it a little bit
closer to the cyclohexane.
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Propoxy cyclohexane.
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But once again the common
name is what you're
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more likely to see.
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Now that we've named a few of
them, let's think a little bit
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about their properties.
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What we've seen already is
that-- and we've used it
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several times, especially in our
Sn2 reactions and things
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like that-- places where
we didn't want
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protons floating around.
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We used actually
diethyl ether.
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And in general ethers do
make for good solvents.
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They tend to be fairly
unreactive.
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So good solvents.
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Especially when you're looking
for an aprotic solvent.
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Remember, aprotic means you
don't have hydrogens that can
[532]
kind of lose their electron to
maybe an electronegative atom
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like an oxygen.
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And then the proton just floats
around, and then can go
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and react with other things.
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This does not have any hydrogens
directly bonded to
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an oxygen in any
of these cases.
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So it is an aprotic solvent.
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And because it doesn't have any
hydrogens bonded to the
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oxygen, you also have
no hydrogen bonding.
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And just as a bit of a review,
you know that in water you
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have the situation-- let me draw
some water molecules-- in
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water you have the situation
where the
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oxygen hogs the electrons.
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So it has a partial
negative charge.
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Hydrogen gets its electrons
hogged or taken away, or it
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spends less time with them.
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So it has a partial
positive charge.
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So this oxygen will have a
partial negative charge.
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And so the hydrogens with the
partial positive charge are
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attracted to the oxygens with
the partial negative charge.
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And you have this hydrogen
bonding.
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And this hydrogen bonding
makes water.
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It pulls the molecules
together.
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So you need to put more energy
into it for it to either melt,
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or for it to actually boil.
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And for the molecules to
kind of get ripped
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away from each other.
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And that's also true
with alcohols.
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Alcohols only have one hydrogen
to each oxygen, but
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they still have the hydrogen
bonding going on.
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In the case of ethers, there
is no hydrogen bonding.
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I'll represent each of
the carbon chains
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with an R and an R.
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I'll write R prime right here
to show that it could be a
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different carbon chain
than this right here.
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And the R stands for radical.
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Not to be confused with
free radical.
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Completely different things.
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This R just means really
a carbon chain
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attached to this oxygen.
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But here there's no hydrogen
getting its electrons hogged
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by oxygens with partial
positive and
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partial negative charges.
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So you're not going to have that
type of hydrogen bonding.
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And because of that, ethers have
much lower melting and
[649]
boiling points.
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It's much easier.
[650]
You have to put less heat into
the system for these molecules
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to break away from each other,
because they aren't attracted
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to each other as much.
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