Keto-enol tautomerization (by Sal)

WEBVTT
Kind: captions
Language: en

00:00:00.460 --> 00:00:03.180
Let's explore another mechanism
that we can have

00:00:03.180 --> 00:00:03.760
with the ketone.

00:00:03.760 --> 00:00:07.180
And actually, an aldehyde can
undergo a very similar or

00:00:07.180 --> 00:00:09.230
actually the same type
of reaction.

00:00:09.230 --> 00:00:13.380
So let's say that I had a ketone
that looked like this.

00:00:13.380 --> 00:00:18.780
Let me draw my carbonyl group,
just like that, and then it is

00:00:18.780 --> 00:00:20.390
bonded to a carbon
that is bonded to

00:00:20.390 --> 00:00:22.680
two other CH3 groups.

00:00:22.680 --> 00:00:25.320
And just to make it clear,
there's three hydrogens off of

00:00:25.320 --> 00:00:26.500
this carbon there implicitly.

00:00:26.500 --> 00:00:28.590
But I'm going to draw the fourth
bond here, which is to

00:00:28.590 --> 00:00:31.180
a hydrogen, because this
hydrogen is going to be

00:00:31.180 --> 00:00:33.630
important for this reaction.

00:00:33.630 --> 00:00:35.490
Now, we know that the
oxygen has two

00:00:35.490 --> 00:00:37.200
lone pairs of electrons.

00:00:37.200 --> 00:00:38.590
Let me draw it up here.

00:00:38.590 --> 00:00:41.270
And let's just imagine it's
floating around in some water,

00:00:41.270 --> 00:00:43.340
and we know that in water
there is some

00:00:43.340 --> 00:00:45.180
concentration of hydronium.

00:00:45.180 --> 00:00:49.540
And let's say that one of the
hydroniums is right over here.

00:00:49.540 --> 00:00:51.400
Hydronium is just positively
charged, so

00:00:51.400 --> 00:00:53.920
this is right here.

00:00:53.920 --> 00:00:55.890
Let me do it in a
different color.

00:00:55.890 --> 00:01:00.320
This is what water looks like.

00:01:00.320 --> 00:01:03.500
And if water gives away an
electron to a proton,

00:01:03.500 --> 00:01:05.790
it looks like this.

00:01:05.790 --> 00:01:08.430
It is hydronium, and then
it only has one

00:01:08.430 --> 00:01:10.330
lone pair of electrons.

00:01:10.330 --> 00:01:13.890
It gave away one of the other
electrons in its other lone

00:01:13.890 --> 00:01:15.670
pair to a proton.

00:01:15.670 --> 00:01:18.010
So you can imagine a reality,
where it's like, hey, I could

00:01:18.010 --> 00:01:20.810
grab that proton from this
hydronium, and then this will

00:01:20.810 --> 00:01:23.280
turn back into water, and in
that situation, the mechanism

00:01:23.280 --> 00:01:25.485
would look like this.

00:01:25.485 --> 00:01:27.360
Let me do it in a
different color.

00:01:27.360 --> 00:01:33.060
This blue electron gets given
to this proton, if they just

00:01:33.060 --> 00:01:36.930
bump into each other just right,
and then the hydrogen's

00:01:36.930 --> 00:01:40.650
electron gets taken
back by what will

00:01:40.650 --> 00:01:42.540
become a water molecule.

00:01:42.540 --> 00:01:46.410
So if that happens, what do our
molecules now look like?

00:01:46.410 --> 00:01:50.650
So now, what was a ketone looks
a little bit different

00:01:50.650 --> 00:01:52.350
than a ketone.

00:01:52.350 --> 00:01:53.910
It looks like this.

00:01:53.910 --> 00:01:57.400
I changed it to a slightly
lighter color of green, so it

00:01:57.400 --> 00:01:58.660
looks like that.

00:01:58.660 --> 00:02:01.390
We have our lone pair over here,
but we no longer have

00:02:01.390 --> 00:02:02.570
this lone pair.

00:02:02.570 --> 00:02:05.990
At this end, we still have this
magenta electron, but now

00:02:05.990 --> 00:02:08.889
it is in a covalent bond with
the blue electron, which was

00:02:08.889 --> 00:02:11.490
now given to the hydrogen
proton.

00:02:11.490 --> 00:02:12.525
Let me scroll up a little bit.

00:02:12.525 --> 00:02:17.230
It was given to this hydrogen
proton up here.

00:02:21.010 --> 00:02:23.860
And then this hydronium
molecule, it took back an

00:02:23.860 --> 00:02:26.280
electron, and now it is
just neutral water.

00:02:30.000 --> 00:02:33.360
It took back that magenta
electron, so now it has two

00:02:33.360 --> 00:02:38.350
lone pairs again, so it
is just neutral water.

00:02:38.350 --> 00:02:41.730
Since this oxygen up here in the
carbonyl group gave away

00:02:41.730 --> 00:02:44.165
an electron, it now has
a positive charge.

00:02:46.920 --> 00:02:51.680
But this is actually resonance
stabilized.

00:02:51.680 --> 00:02:55.670
You could maybe see that this
would be in resonance, or

00:02:55.670 --> 00:02:59.760
another resonance form of this
would be-- if this guy's

00:02:59.760 --> 00:03:03.290
positive, so he wants to gain an
electron, so maybe he takes

00:03:03.290 --> 00:03:06.830
an electron from this carbon,
the carbon in the carbonyl

00:03:06.830 --> 00:03:07.810
group right over there.

00:03:07.810 --> 00:03:11.420
So if you takes that electron,
then the other resonance form

00:03:11.420 --> 00:03:13.370
would look like this.

00:03:13.370 --> 00:03:15.460
Let me doing it in
the same colors.

00:03:15.460 --> 00:03:20.150
You have now only a single bond
with this oxygen up here.

00:03:20.150 --> 00:03:23.430
This carbon down here is still
bonded to the same carbons,

00:03:23.430 --> 00:03:25.480
and then this carbon over here,
we could call this an

00:03:25.480 --> 00:03:26.600
alpha carbon.

00:03:26.600 --> 00:03:29.110
This is an alpha carbon
to the carbonyl group.

00:03:29.110 --> 00:03:32.290
It still has a hydrogen on
it right over there.

00:03:32.290 --> 00:03:37.010
And this oxygen, since it gained
this magenta electron,

00:03:37.010 --> 00:03:38.260
now it has two lone pairs.

00:03:38.260 --> 00:03:41.660
It has this pair over there,
and then it gained this

00:03:41.660 --> 00:03:44.200
electron and this electron, so
it has another lone pair.

00:03:44.200 --> 00:03:48.510
And, of course, it has the
bond to the hydrogen.

00:03:48.510 --> 00:03:51.660
Since it gained an electron,
it is now neutral.

00:03:51.660 --> 00:03:55.710
This carbon lost an electron,
so now it is positive.

00:03:55.710 --> 00:04:01.040
So now this carbon right over
here is positive, and these

00:04:01.040 --> 00:04:03.020
two are two different resonance
forms, so they help

00:04:03.020 --> 00:04:03.970
stabilize each other.

00:04:03.970 --> 00:04:06.480
And the reality is actually
someplace in between.

00:04:06.480 --> 00:04:08.950
I could actually draw it in
brackets to show that these

00:04:08.950 --> 00:04:12.500
are two resonance structures.

00:04:12.500 --> 00:04:15.320
Now, you can imagine, just as
likely-- and actually, I

00:04:15.320 --> 00:04:17.920
shouldn't just draw this as a
one-way arrow, because this

00:04:17.920 --> 00:04:21.200
guy could take a hydrogen from
this hydronium, or a water

00:04:21.200 --> 00:04:23.470
could take a hydrogen from this
guy, so this actually

00:04:23.470 --> 00:04:25.680
could go in both directions.

00:04:25.680 --> 00:04:26.620
So let me make that clear.

00:04:26.620 --> 00:04:29.835
This could go in both
directions.

00:04:29.835 --> 00:04:32.890
You could say that they're in
equilibrium with each other.

00:04:32.890 --> 00:04:34.740
You're just as likely to go in
that direction as you really,

00:04:34.740 --> 00:04:37.070
for the most part, are to go
on the other direction.

00:04:37.070 --> 00:04:41.060
But you can now imagine, this
has now turned from a carbonyl

00:04:41.060 --> 00:04:44.740
group, this has now an OH group,
this has now turned

00:04:44.740 --> 00:04:47.520
into an alcohol, although we
have this carbocation here,

00:04:47.520 --> 00:04:49.920
that this does not like
being positive.

00:04:49.920 --> 00:04:54.690
And so you could imagine where
this electron right here on

00:04:54.690 --> 00:04:58.760
this hydrogen nucleus might want
to go really bad to this

00:04:58.760 --> 00:05:01.720
carbocation, and it just needs
something to nab the proton

00:05:01.720 --> 00:05:03.240
off for it to go there.

00:05:03.240 --> 00:05:04.970
And the perfect candidate
for that would

00:05:04.970 --> 00:05:06.240
just be a water molecule.

00:05:06.240 --> 00:05:08.550
We have this water floating
around, so let me draw another

00:05:08.550 --> 00:05:11.680
water molecule, just
like this.

00:05:11.680 --> 00:05:14.440
It has two lone pairs.

00:05:14.440 --> 00:05:16.290
It can act as a weak base.

00:05:16.290 --> 00:05:18.930
It can give one of
its electrons to

00:05:18.930 --> 00:05:20.240
this hydrogen proton.

00:05:20.240 --> 00:05:22.830
If it does that at the exact
same time, bumps into it in

00:05:22.830 --> 00:05:27.860
the exact same way, this
electron can then go to the

00:05:27.860 --> 00:05:28.960
carbocation.

00:05:28.960 --> 00:05:33.980
And if that happened, you could
go in either direction.

00:05:33.980 --> 00:05:36.130
This reaction is just as
likely to happen as the

00:05:36.130 --> 00:05:38.150
reverse reaction, so we could
put this in equilibrium.

00:05:40.710 --> 00:05:43.990
But if that were to happen, then
what started off as our

00:05:43.990 --> 00:05:47.510
ketone now looks like this.

00:05:47.510 --> 00:05:53.970
We have a bond to an OH group
just like this, and over

00:05:53.970 --> 00:05:56.770
here-- actually, let me
draw the rest of it.

00:05:56.770 --> 00:05:59.130
We had our molecule that looked
like that, but now,

00:05:59.130 --> 00:06:01.860
this electron gets giving back
to this carbocation.

00:06:01.860 --> 00:06:07.940
We now have a double bond here
between what was a carbonyl

00:06:07.940 --> 00:06:09.780
carbon and our alpha carbon.

00:06:09.780 --> 00:06:13.130
So now we have this double
bond right over here.

00:06:16.320 --> 00:06:19.320
That hydrogen has been
taken by the water,

00:06:19.320 --> 00:06:20.680
and now that is hydronium.

00:06:20.680 --> 00:06:23.990
So let me draw the water
or the hydronium.

00:06:23.990 --> 00:06:27.270
So that water, it had that one
lone pair, and then the other

00:06:27.270 --> 00:06:29.570
lone pair got broken up, because
it gave one of the

00:06:29.570 --> 00:06:33.270
electrons to this hydrogen right
over here, and it went

00:06:33.270 --> 00:06:34.850
back to being hydronium.

00:06:34.850 --> 00:06:35.700
So what happened here?

00:06:35.700 --> 00:06:42.270
We started with a ketone, and
they sometimes will call this

00:06:42.270 --> 00:06:46.040
the keto form of the molecule,
and then we ended up with

00:06:46.040 --> 00:06:48.050
something called
the enol form.

00:06:51.620 --> 00:06:59.690
An enol comes from the fact that
it is an alkene that is

00:06:59.690 --> 00:07:00.545
also an alcohol.

00:07:00.545 --> 00:07:02.110
You could even call
it an alkenol.

00:07:02.110 --> 00:07:04.960
It has a double bond, and on one
of the carbons that has a

00:07:04.960 --> 00:07:07.960
double bond, it has
an OH group.

00:07:07.960 --> 00:07:09.870
And the whole reason I show you
this mechanism is, one,

00:07:09.870 --> 00:07:11.870
just to show you a mechanism
that could happen with an

00:07:11.870 --> 00:07:13.260
aldehyde or a ketone.

00:07:13.260 --> 00:07:15.590
This was a ketone, but if this
was a hydrogen right here,

00:07:15.590 --> 00:07:18.570
this would have been occurring
with an aldehyde.

00:07:18.570 --> 00:07:21.380
But even more, this is a pretty
common mechanism that

00:07:21.380 --> 00:07:22.950
you'll see in organic chemistry
classes, and

00:07:22.950 --> 00:07:24.430
actually has a lot of functions

00:07:24.430 --> 00:07:26.260
in biology, in general.

00:07:26.260 --> 00:07:31.670
And these two molecules, this
ketone and this enol form,

00:07:31.670 --> 00:07:32.920
these are called tautomers.

00:07:38.740 --> 00:07:42.400
And the keto form is actually
the much more stable form.

00:07:42.400 --> 00:07:45.800
In a solution, you won't see
much of the enol form, but

00:07:45.800 --> 00:07:46.575
these can occur.

00:07:46.575 --> 00:07:50.440
It can spontaneously through
equilibrium get to

00:07:50.440 --> 00:07:52.320
the actual enol form.

00:07:52.320 --> 00:07:54.870
And so you could imagine, these
are tautomers, so this

00:07:54.870 --> 00:07:58.210
mechanism is actually called a
tautomerization, and these are

00:07:58.210 --> 00:08:01.620
the keto and enol forms
of the tautomers.


Amine naming introduction

WEBVTT
Kind: captions
Language: en

00:00:00.560 --> 00:00:03.830
Let's see if we can handle some
slightly more difficult

00:00:03.830 --> 00:00:05.210
amine naming examples.

00:00:05.210 --> 00:00:08.210
So if we look at this blue
molecule right here, we always

00:00:08.210 --> 00:00:11.170
want to start off by finding
the longest carbon chain.

00:00:11.170 --> 00:00:13.480
It looks like it's this chain
at the bottom where we have

00:00:13.480 --> 00:00:19.870
one, two, three, four, five,
six, seven, eight carbons.

00:00:19.870 --> 00:00:22.530
So it's going to be octan.

00:00:22.530 --> 00:00:24.640
We don't want to just call it
octane because we have these

00:00:24.640 --> 00:00:27.340
functional groups up here, and
maybe one of them's going to

00:00:27.340 --> 00:00:29.290
take higher priority
than just the fact

00:00:29.290 --> 00:00:30.000
that this is an alkane.

00:00:30.000 --> 00:00:31.610
And, in fact, one
of them will.

00:00:31.610 --> 00:00:32.850
So let's look at them.

00:00:32.850 --> 00:00:35.340
So over here we an
amino group.

00:00:35.340 --> 00:00:37.310
That would make this
molecule an amine.

00:00:37.310 --> 00:00:40.170
So this is an amino
group right here.

00:00:40.170 --> 00:00:44.500
Then we have this
benzene ring.

00:00:44.500 --> 00:00:46.540
And when benzene is a functional
group, we call it a

00:00:46.540 --> 00:00:47.790
phenyl group.

00:00:50.680 --> 00:00:53.600
And that's derived from I think
it's either the Greek or

00:00:53.600 --> 00:00:57.170
the Latin word for light because
benzene was first

00:00:57.170 --> 00:01:00.430
isolated from, I guess, the
air around lanterns or

00:01:00.430 --> 00:01:02.360
something, so this is called
a phenyl group.

00:01:02.360 --> 00:01:04.670
And then finally we have this
OH, which would make this

00:01:04.670 --> 00:01:07.590
whole thing an alcohol, or we
could call that a hydroxy

00:01:07.590 --> 00:01:12.600
group, so this right here
is a hydroxy group.

00:01:12.600 --> 00:01:15.550
Now, this is just something
that you need to know.

00:01:15.550 --> 00:01:17.560
There's no way to kind
of deduce it.

00:01:17.560 --> 00:01:20.025
The people who've decided how
to name things just decided

00:01:20.025 --> 00:01:22.990
that certain groups take higher
priority over others.

00:01:22.990 --> 00:01:26.170
And out of these three groups,
the hydroxy group, the thing

00:01:26.170 --> 00:01:29.470
that's making this whole thing
an alcohol, takes the highest

00:01:29.470 --> 00:01:32.790
priority, so this is what's
going to define the suffix.

00:01:32.790 --> 00:01:35.145
So if we start numbering, we
want to start numbering this

00:01:35.145 --> 00:01:37.870
chain closest to the highest
priority group.

00:01:37.870 --> 00:01:39.310
So we'll start numbering
at this end.

00:01:39.310 --> 00:01:47.250
So it's one, two, three, four,
five, six, seven, eight.

00:01:47.250 --> 00:01:50.570
So we have a hydroxy group on
the three carbon, so this is

00:01:50.570 --> 00:01:51.820
octan-3-ol.

00:01:56.860 --> 00:01:58.960
If this was not a high priority,
we would put a

00:01:58.960 --> 00:02:00.790
hydroxy in the front, but since
this is the highest

00:02:00.790 --> 00:02:03.720
prioritiy, its defining this
as an alcohol, octanol.

00:02:03.720 --> 00:02:06.290
But we put the 3 there to say
it's on the three carbon.

00:02:06.290 --> 00:02:09.120
And then, of course, this
would be 5-phenyl.

00:02:09.120 --> 00:02:10.930
This right here is 5-phenyl.

00:02:14.420 --> 00:02:18.470
And this right here
is 8-amino.

00:02:18.470 --> 00:02:21.470
And amino comes before phenyl in
alphabetical order, so this

00:02:21.470 --> 00:02:24.230
whole molecule is going to
be-- let me write it over

00:02:24.230 --> 00:02:25.480
here-- it's going to be
8-amino-5-phenyl-octan-3-ol.

00:02:36.780 --> 00:02:38.030
And we're done.

00:02:45.920 --> 00:02:49.540
So this is an aromatic compound
because of the

00:02:49.540 --> 00:02:50.300
benzene ring.

00:02:50.300 --> 00:02:52.730
It's an amine because
of the amino group.

00:02:52.730 --> 00:02:56.890
And it's an alcohol because
of the hydroxy group.

00:02:56.890 --> 00:02:58.810
Now let's look at this molecule
here in green.

00:02:58.810 --> 00:03:00.500
And actually, I forgot
to draw part of it.

00:03:00.500 --> 00:03:02.160
This is supposed to
be a benzene ring.

00:03:02.160 --> 00:03:03.720
So let me make clear.

00:03:03.720 --> 00:03:05.975
That is a benzene ring.

00:03:05.975 --> 00:03:07.740
So let's think about
the different

00:03:07.740 --> 00:03:08.800
functional groups here.

00:03:08.800 --> 00:03:10.750
And we'll start with the one
that you've probably never

00:03:10.750 --> 00:03:12.000
seen before.

00:03:12.000 --> 00:03:18.240
This is a nitro group, and
it's highly explosive.

00:03:18.240 --> 00:03:20.800
Maybe in a future video, I'll
show you some nitroglycerin

00:03:20.800 --> 00:03:24.860
and some TNT, as you know, which
are highly explosive,

00:03:24.860 --> 00:03:26.720
but they have nitro
groups on them.

00:03:26.720 --> 00:03:31.040
So this right here
is a nitro group.

00:03:31.040 --> 00:03:33.750
It takes very low precedence in
the whole scheme of things.

00:03:33.750 --> 00:03:39.480
So this will never be the cause
of naming the suffix.

00:03:39.480 --> 00:03:41.970
We just know that this is a
nitro group right here.

00:03:41.970 --> 00:03:44.970
We, of course, have
a bromo group that

00:03:44.970 --> 00:03:46.820
we've seen many times.

00:03:46.820 --> 00:03:48.980
That is a bromo group.

00:03:48.980 --> 00:03:53.230
And then we have an amino
group right here.

00:03:53.230 --> 00:03:54.760
So this is going to be--
let me do this

00:03:54.760 --> 00:03:56.110
in a different color.

00:03:56.110 --> 00:04:00.220
This is definitely an amine.

00:04:00.220 --> 00:04:03.440
This is an amino group
right there.

00:04:06.890 --> 00:04:09.315
And out of these three groups,
the amino group is definitely

00:04:09.315 --> 00:04:10.600
of the highest priority.

00:04:10.600 --> 00:04:13.552
So you might be tempted to name
this 1-amino-2,3-brom

00:04:13.552 --> 00:04:21.540
o-4-nitrobenzene, but when a
benzene ring is attached to an

00:04:21.540 --> 00:04:25.080
amino group, this one also has
one of those special names.

00:04:25.080 --> 00:04:26.930
And let me just do it on
the side right here.

00:04:26.930 --> 00:04:35.650
So if I just have a benzene
ring attached to an amino

00:04:35.650 --> 00:04:40.330
group, so that's an NH2 right
there, we call this molecule

00:04:40.330 --> 00:04:42.515
right here, and this is just
the common name for it and

00:04:42.515 --> 00:04:45.910
it's something to put in your
toolkit, this is aniline.

00:04:49.910 --> 00:04:51.710
So that will be the base name.

00:04:51.710 --> 00:04:57.800
This whole thing right
here we call aniline.

00:04:57.800 --> 00:04:58.900
Let me write it over here.

00:04:58.900 --> 00:05:00.440
So this is aniline.

00:05:03.030 --> 00:05:05.280
And then we always want to start
numbering at the group

00:05:05.280 --> 00:05:07.400
that's really defining the
molecules, so we start

00:05:07.400 --> 00:05:08.260
numbering here.

00:05:08.260 --> 00:05:10.110
And you want to go in the order
where you're going to

00:05:10.110 --> 00:05:14.220
bump into something first. So,
one, two, three, four.

00:05:14.220 --> 00:05:17.610
So this is going to be-- if we
look at them, and bromo comes

00:05:17.610 --> 00:05:20.320
alphabetically before nitro,
so it's going to be

00:05:20.320 --> 00:05:21.570
3-bromo-4-nitroaniline.

00:05:40.040 --> 00:05:41.950
And we are done!


Naming benzene derivatives introduction

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:04.910
I mentioned in the last video
that 99% of the aromatic

00:00:04.910 --> 00:00:08.330
compounds that you'll see in a
chemistry or organic chemistry

00:00:08.330 --> 00:00:12.240
class is either going to be
benzene or a molecule derived

00:00:12.240 --> 00:00:13.490
from benzene.

00:00:16.250 --> 00:00:19.370
So what I want to do in this
video is just familiarize you

00:00:19.370 --> 00:00:22.350
with some of these molecules
and how to name them.

00:00:22.350 --> 00:00:23.810
So you know what you're
looking at.

00:00:23.810 --> 00:00:26.730
Or I guess so you could name
what you're looking at.

00:00:26.730 --> 00:00:28.440
So you've seen this
multiple times.

00:00:28.440 --> 00:00:29.850
Benzene just looks like this.

00:00:29.850 --> 00:00:33.300
It's a six carbon ring with
three double bonds.

00:00:33.300 --> 00:00:34.900
These three double
bonds like that.

00:00:34.900 --> 00:00:37.260
And that's not it's only
configuration.

00:00:37.260 --> 00:00:41.000
Sometimes it's shown to
be in resonance with

00:00:41.000 --> 00:00:43.060
this form right here.

00:00:43.060 --> 00:00:47.030
So the double bonds all flip
around the circle, like that.

00:00:47.030 --> 00:00:48.960
Or sometimes it's simply
drawn like this.

00:00:48.960 --> 00:00:50.870
And I talked about this
in the last video.

00:00:50.870 --> 00:00:53.290
Just to show that really
neither of these

00:00:53.290 --> 00:00:55.200
configurations is
exactly right.

00:00:55.200 --> 00:00:59.690
That these pi electrons, they're
just moving around the

00:00:59.690 --> 00:01:01.670
entire ring.

00:01:01.670 --> 00:01:04.930
So and sometimes you'll just
have the hexagon with a circle

00:01:04.930 --> 00:01:07.720
on the inside to show that the
pi electrons are just floating

00:01:07.720 --> 00:01:09.710
around the entire ring.

00:01:09.710 --> 00:01:13.360
Now if I were to add something
to the benzene ring, it's

00:01:13.360 --> 00:01:14.810
pretty straightforward
to name it.

00:01:14.810 --> 00:01:17.000
So say I have this molecule
right here.

00:01:19.860 --> 00:01:20.880
So let's see I have that.

00:01:20.880 --> 00:01:22.120
That's benzene.

00:01:22.120 --> 00:01:24.250
But let's say this carbon
over here, it has

00:01:24.250 --> 00:01:25.810
one, two, three bonds.

00:01:25.810 --> 00:01:27.810
If I didn't draw anything else,
you'd just assume that

00:01:27.810 --> 00:01:29.340
there's also a hydrogen here.

00:01:29.340 --> 00:01:32.380
But maybe there's no
hydrogen there.

00:01:32.380 --> 00:01:34.340
Let me do this in a
different color.

00:01:34.340 --> 00:01:37.550
Maybe you have a
chlorine there.

00:01:37.550 --> 00:01:43.630
Well this is just
chlorobenzene.

00:01:46.590 --> 00:01:49.410
If that was a bromine, it
would be bromobenzene.

00:01:49.410 --> 00:01:52.320
So pretty straightforward.

00:01:52.320 --> 00:01:53.230
Let me draw it.

00:01:53.230 --> 00:01:56.340
Let me actually change
it a little bit.

00:01:56.340 --> 00:01:57.950
Let's say you had
a chloro there.

00:01:57.950 --> 00:02:00.980
And let's say you had,
oh I don't know.

00:02:00.980 --> 00:02:05.140
Let's say you had a
bromo over here.

00:02:05.140 --> 00:02:08.610
Let's say you have a
bromo over there.

00:02:08.610 --> 00:02:09.860
Draw the bromo.

00:02:12.140 --> 00:02:14.000
So you can just start
numbering.

00:02:14.000 --> 00:02:16.090
You can actually start numbering
in either place.

00:02:16.090 --> 00:02:17.750
Let's start with the bromine.

00:02:17.750 --> 00:02:19.400
It's alphabetically in front.

00:02:19.400 --> 00:02:27.170
So this would be 1-bromo,
2-chlorobenzene.

00:02:30.860 --> 00:02:32.200
Pretty straightforward.

00:02:32.200 --> 00:02:33.640
Now it gets a little
bit more involved.

00:02:33.640 --> 00:02:37.950
The IUPAC, which we know is kind
of the group that named

00:02:37.950 --> 00:02:39.200
most things.

00:02:41.390 --> 00:02:43.710
Everything else we've seen so
far, they came up with a

00:02:43.710 --> 00:02:46.090
separate naming mechanism
from the common names.

00:02:46.090 --> 00:02:49.930
But benzene, it's so ingrained
in the organic chemistry

00:02:49.930 --> 00:02:53.190
community, that all of the
benzene or benzene derivative

00:02:53.190 --> 00:02:55.160
molecules, they just kind of
said, well you know what,

00:02:55.160 --> 00:02:57.630
we're just going to use the
names that everyone uses.

00:02:57.630 --> 00:03:01.170
So here's a couple of common
benzene derivatives.

00:03:01.170 --> 00:03:04.470
So if you have this molecule
right here.

00:03:04.470 --> 00:03:08.120
Let me-- if you have this
molecule right here-- I'll

00:03:08.120 --> 00:03:10.510
actually draw the pi electrons
as a circle.

00:03:10.510 --> 00:03:12.550
Actually I'll draw it with
the double bonds.

00:03:12.550 --> 00:03:14.530
So let's say you have this
molecule right here.

00:03:14.530 --> 00:03:18.470
And over here you have an OH.

00:03:18.470 --> 00:03:20.300
You have an OH right there.

00:03:20.300 --> 00:03:21.550
This is called a phenol.

00:03:24.630 --> 00:03:26.980
So it's not called a
benzene anymore.

00:03:26.980 --> 00:03:33.700
And if you had a molecule
that looked like this,

00:03:33.700 --> 00:03:36.010
so just like a phenol.

00:03:36.010 --> 00:03:39.130
So essentially it is a phenol.

00:03:39.130 --> 00:03:43.140
But let's say you have a
bromine right there.

00:03:43.140 --> 00:03:46.670
What you do is you start
numbering at the group that's

00:03:46.670 --> 00:03:47.940
making this is a phenol.

00:03:47.940 --> 00:03:49.050
So you start numbering there.

00:03:49.050 --> 00:03:51.380
One and then you
get to the two.

00:03:51.380 --> 00:03:53.140
So this is 2-bromo.

00:03:53.140 --> 00:03:54.390
This is 2-bromophenol.

00:04:00.710 --> 00:04:02.970
And unfortunately this is one of
those things that you just

00:04:02.970 --> 00:04:04.810
kind of have to memorize.

00:04:04.810 --> 00:04:09.180
That a phenol is really just a
benzene ring with an OH group.

00:04:09.180 --> 00:04:12.570
Another one that is probably
a good idea to memorize.

00:04:12.570 --> 00:04:15.130
I mean at least for me in
organic chemistry, the most

00:04:15.130 --> 00:04:17.019
confusing thing is when someone
says the name of a

00:04:17.019 --> 00:04:19.490
molecule that sounds like they
expect you to understand.

00:04:19.490 --> 00:04:20.459
But you don't understand it.

00:04:20.459 --> 00:04:22.420
So it's, I guess, a good
idea to understand as

00:04:22.420 --> 00:04:24.270
many names as possible.

00:04:24.270 --> 00:04:27.140
So if you just have a benzene
ring, and you just have a

00:04:27.140 --> 00:04:32.190
methyl group attached to
that benzene ring,

00:04:32.190 --> 00:04:33.780
this is called toluene.

00:04:36.810 --> 00:04:44.550
And once again let's
say you had a

00:04:44.550 --> 00:04:47.070
fluorine right over there.

00:04:47.070 --> 00:04:52.240
This would be one, two,
three fluorotulene.

00:04:52.240 --> 00:04:53.500
I always have trouble
saying that.

00:04:53.500 --> 00:04:55.560
So it's one, two, three.

00:04:55.560 --> 00:04:56.940
You start at the group
that's kind of

00:04:56.940 --> 00:04:59.170
making this the toluene.

00:04:59.170 --> 00:05:00.610
So let me make it a little
bit clearer.

00:05:00.610 --> 00:05:03.805
So this would be
3-fluorotoluene.

00:05:07.540 --> 00:05:08.560
This would all be in one word.

00:05:08.560 --> 00:05:11.560
I just wrote it up here
to save some space.

00:05:11.560 --> 00:05:13.910
Now a couple of other ones
that you'll see.

00:05:13.910 --> 00:05:17.640
And once again, as you know, if
you watched many, many Khan

00:05:17.640 --> 00:05:20.040
Academy videos, I hate
memorizing things.

00:05:20.040 --> 00:05:21.300
But these are just names.

00:05:21.300 --> 00:05:23.330
And these aren't systematically
derived.

00:05:23.330 --> 00:05:25.540
The chemistry community just
uses them, because that's the

00:05:25.540 --> 00:05:26.340
way they've heard them.

00:05:26.340 --> 00:05:28.750
So it is one of those things you
kind of have to memorize.

00:05:28.750 --> 00:05:37.560
So if you have a benzene ring,
where the functional group

00:05:37.560 --> 00:05:41.060
that is kind of defining the
benzene ring, it's essentially

00:05:41.060 --> 00:05:42.070
becoming an amine.

00:05:42.070 --> 00:05:44.850
We haven't actually covered
videos on amines yet.

00:05:44.850 --> 00:05:46.130
And I'll do that in
a future video.

00:05:46.130 --> 00:05:49.410
But it's essentially, it's
replaced one of the hydrogens

00:05:49.410 --> 00:05:51.660
in ammonia.

00:05:51.660 --> 00:05:52.690
Let me draw ammonia.

00:05:52.690 --> 00:05:58.630
Ammonia has three hydrogens
and one lone pair.

00:05:58.630 --> 00:06:01.250
Here we've replaced one
of the hydrogens.

00:06:01.250 --> 00:06:02.640
Actually there's two
hydrogens here.

00:06:02.640 --> 00:06:06.090
We've replaced one of the
hydrogens with a benzene ring.

00:06:06.090 --> 00:06:07.700
This type of thing you
call an aniline.

00:06:13.480 --> 00:06:13.950
Right there.

00:06:13.950 --> 00:06:14.860
And the same idea.

00:06:14.860 --> 00:06:19.400
If I put a fluoro here, this
would be 2-fluoroaniline.

00:06:19.400 --> 00:06:22.970
So you use whatever the base
molecule is, and then you just

00:06:22.970 --> 00:06:26.020
name it, really the way we've
named a lot of things before.

00:06:26.020 --> 00:06:28.530
And I'll just introduce you to
two more, just so that you

00:06:28.530 --> 00:06:29.560
have them under your belt.

00:06:29.560 --> 00:06:32.290
So that you'll have seen them
before if anyone introduces

00:06:32.290 --> 00:06:33.210
them to you.

00:06:33.210 --> 00:06:35.160
And they're really introducing
groups that we'll study in

00:06:35.160 --> 00:06:36.310
more detail in the future.

00:06:36.310 --> 00:06:39.650
But if you have a benzene
ring once again.

00:06:39.650 --> 00:06:42.180
So we have a benzene ring.

00:06:42.180 --> 00:06:44.730
And then you have a
carboxyl group.

00:06:44.730 --> 00:06:47.900
And we'll talk more about
carboxyl groups in the future.

00:06:47.900 --> 00:06:50.010
But it creates carboxylic
acid.

00:06:50.010 --> 00:06:52.490
This thing right here, this
hydrogen, it can actually be

00:06:52.490 --> 00:06:53.560
released quite easily.

00:06:53.560 --> 00:06:55.480
And we'll talk about
that in the future.

00:06:55.480 --> 00:06:58.305
This right here is called
benzoic acid.

00:07:01.230 --> 00:07:04.380
And this name, actually
there is a little bit

00:07:04.380 --> 00:07:05.430
more logic to this.

00:07:05.430 --> 00:07:08.330
You have the benz part
for the benzene.

00:07:08.330 --> 00:07:09.880
So let me make this in
different colors.

00:07:09.880 --> 00:07:13.400
The benzene part, that gives
us the benz right there.

00:07:13.400 --> 00:07:19.130
And then in general, whenever
you have a carboxyl group like

00:07:19.130 --> 00:07:21.680
this, it becomes a
carboxylic acid.

00:07:21.680 --> 00:07:24.600
And you tend to add the
-oic acid to the end.

00:07:24.600 --> 00:07:28.750
So this actually has some
logical naming to it.

00:07:28.750 --> 00:07:30.620
Now the last one I'll introduce
you to is very

00:07:30.620 --> 00:07:31.120
similar to this.

00:07:31.120 --> 00:07:35.100
Instead of having an OH right
here, we just have a hydrogen.

00:07:35.100 --> 00:07:36.590
It would be an aldehyde.

00:07:36.590 --> 00:07:37.590
So let me draw that.

00:07:37.590 --> 00:07:38.930
And you could almost
imagine what

00:07:38.930 --> 00:07:39.600
that's going to be called.

00:07:39.600 --> 00:07:40.920
It's benzaldehyde.

00:07:40.920 --> 00:07:42.150
So let me draw it.

00:07:42.150 --> 00:07:43.650
So you have your benzene ring.

00:07:46.760 --> 00:07:50.400
And then instead of this
carboxyl group, you have an

00:07:50.400 --> 00:07:52.990
aldehyde group.

00:07:52.990 --> 00:07:53.810
You have your carbon.

00:07:53.810 --> 00:07:55.200
There's implicitly
a carbon here.

00:07:55.200 --> 00:07:57.230
Let me make that, just in
case it's the first time

00:07:57.230 --> 00:07:58.090
you're seeing it.

00:07:58.090 --> 00:07:58.930
You have a carbon there.

00:07:58.930 --> 00:08:03.030
Instead of an OH group, you
have just a hydrogen.

00:08:03.030 --> 00:08:06.240
And so once again you
have a benzene.

00:08:06.240 --> 00:08:09.780
So it actually makes sense to
put the benz over there.

00:08:09.780 --> 00:08:11.900
And then you have the
aldehyde group.

00:08:11.900 --> 00:08:14.730
Then you have an aldehyde
group right over here.

00:08:14.730 --> 00:08:18.205
So this is called a
benzaldehyde, or this molecule

00:08:18.205 --> 00:08:21.470
is called benzaldehyde.

00:08:21.470 --> 00:08:27.940
And we'll study amines and
aldehydes and carboxylic acids

00:08:27.940 --> 00:08:30.540
in much more detail in future
videos, and actually see

00:08:30.540 --> 00:08:31.710
reactions that involve them.

00:08:31.710 --> 00:08:33.770
But I just wanted to
expose you to this.

00:08:33.770 --> 00:08:36.929
And so when you see these kinds
of names, you don't

00:08:36.929 --> 00:08:38.179
become intimidated.


Aromatic Compounds and Huckel's Rule

WEBVTT
Kind: captions
Language: en

00:00:00.520 --> 00:00:03.545
We touched on this in the video
on resonance, but I want

00:00:03.545 --> 00:00:06.666
to devote an entire video
to aromatic compounds.

00:00:13.180 --> 00:00:17.440
And one of the big mysteries in
chemistry is why they were

00:00:17.440 --> 00:00:19.170
named aromatic compounds.

00:00:19.170 --> 00:00:21.820
Because you know it clearly
comes from the word aroma.

00:00:21.820 --> 00:00:25.370
So one would think maybe all of
these compounds smell good,

00:00:25.370 --> 00:00:27.150
or smell bad, or don't
smell at all.

00:00:27.150 --> 00:00:29.060
But actually it turns out
that a lot of them don't

00:00:29.060 --> 00:00:30.130
even smell at all.

00:00:30.130 --> 00:00:31.260
So it's a little bit
of a mystery.

00:00:31.260 --> 00:00:33.800
Some people think that they
have some relation, the

00:00:33.800 --> 00:00:36.590
gentleman who named them, saw
that they had some chemical

00:00:36.590 --> 00:00:39.210
relation to things that did
smell, so that he named them

00:00:39.210 --> 00:00:40.250
aromatic compounds.

00:00:40.250 --> 00:00:42.210
So it is a bit of a mystery.

00:00:42.210 --> 00:00:45.520
In general, the most common
aromatic compound-- and really

00:00:45.520 --> 00:00:48.210
this is like 99% of the time
what you're going to see in

00:00:48.210 --> 00:00:52.150
chemistry class as an aromatic
compound-- is either benzene

00:00:52.150 --> 00:00:54.580
or a molecule derived
from benzene.

00:00:54.580 --> 00:00:56.720
Let me draw benzene
right here.

00:00:56.720 --> 00:01:01.510
So benzene is normally
drawn like this.

00:01:01.510 --> 00:01:03.640
So it's a six carbon ring.

00:01:03.640 --> 00:01:05.710
And it has three double bonds.

00:01:05.710 --> 00:01:08.490
It has three double
bonds like that.

00:01:08.490 --> 00:01:11.170
And we learned in the resonance
video, that this

00:01:11.170 --> 00:01:15.170
isn't actually the only
configuration for benzene.

00:01:15.170 --> 00:01:18.130
It could just as likely be
in this configuration.

00:01:18.130 --> 00:01:21.300
That this electron up here, this
electron up here, might

00:01:21.300 --> 00:01:21.940
move there.

00:01:21.940 --> 00:01:23.680
This electron might
move over there.

00:01:23.680 --> 00:01:26.190
And then this electron might
move over there.

00:01:26.190 --> 00:01:29.670
Let me clear that up, so you
don't make it too confusing.

00:01:29.670 --> 00:01:33.140
So it could just as likely
be in this configuration.

00:01:33.140 --> 00:01:37.490
It could just as likely be in
this configuration right here,

00:01:37.490 --> 00:01:41.690
where the double bonds are on
the other bonds that aren't

00:01:41.690 --> 00:01:43.170
double bonded over here.

00:01:43.170 --> 00:01:45.260
So it could just as easily
be over there.

00:01:45.260 --> 00:01:46.470
And we learned in the resonance
video that the

00:01:46.470 --> 00:01:49.040
reality is that it's actually
in between.

00:01:49.040 --> 00:01:50.600
And sometimes it's
drawn like this.

00:01:50.600 --> 00:01:53.240
It's going back and forth
between these configurations.

00:01:53.240 --> 00:01:56.620
But the reality-- and
you'll sometimes see

00:01:56.620 --> 00:01:58.850
it drawn like this.

00:01:58.850 --> 00:02:02.930
You'll sometimes see it drawn
like this, with just a circle

00:02:02.930 --> 00:02:07.450
in between, in the middle of the
hexane ring, I guess you

00:02:07.450 --> 00:02:10.020
could say, or the
benzene ring.

00:02:10.020 --> 00:02:13.350
Which is showing that the
electrons, those pi electrons,

00:02:13.350 --> 00:02:15.880
those electrons that form the
double bond are actually just,

00:02:15.880 --> 00:02:17.300
they're going back and
forth between this.

00:02:17.300 --> 00:02:19.630
They're just spreading around
the entire ring.

00:02:19.630 --> 00:02:23.350
And what makes aromatic
compounds interesting is

00:02:23.350 --> 00:02:28.340
because these pi electrons can
spread around the entire ring,

00:02:28.340 --> 00:02:31.750
it's actually a much more stable
configuration, or a

00:02:31.750 --> 00:02:34.460
much more stable molecule, than
what you would predict if

00:02:34.460 --> 00:02:38.800
you just looked at one of these
two configurations.

00:02:38.800 --> 00:02:40.670
Another way that it's
often drawn looks

00:02:40.670 --> 00:02:42.600
something like this.

00:02:42.600 --> 00:02:44.490
And I'm just doing it in yellow,
just to have something

00:02:44.490 --> 00:02:45.640
in a different color.

00:02:45.640 --> 00:02:47.830
Sometimes you'll just see
this, that you know, is

00:02:47.830 --> 00:02:49.160
someplace in between
that and that.

00:02:49.160 --> 00:02:52.050
So you'll have a dotted line
there, dotted line, dotted

00:02:52.050 --> 00:02:55.210
line, dotted line, dotted
line, dotted line.

00:02:55.210 --> 00:02:59.740
This is the most common kind of
short hand for showing both

00:02:59.740 --> 00:03:02.770
benzene and for showing that
it's experiencing this

00:03:02.770 --> 00:03:04.860
resonance, that you have
this conjugated

00:03:04.860 --> 00:03:06.540
system of pi electrons.

00:03:06.540 --> 00:03:08.540
And I'll help you visualize
that in a second.

00:03:08.540 --> 00:03:10.990
But you also might see
something like this.

00:03:10.990 --> 00:03:13.640
It can go back and forth, and
everything in between, between

00:03:13.640 --> 00:03:15.220
these two configurations.

00:03:15.220 --> 00:03:17.330
Now just to visualize
what's going on.

00:03:17.330 --> 00:03:19.970
Because you'll sometimes hear
people talk about conjugated

00:03:19.970 --> 00:03:21.470
system of pi electrons.

00:03:21.470 --> 00:03:25.080
I want to actually think about,
help a little bit more

00:03:25.080 --> 00:03:28.010
visualizing what the molecule
might look like in three

00:03:28.010 --> 00:03:29.260
dimensions.

00:03:31.980 --> 00:03:35.410
So that is the six carbon
ring right there.

00:03:35.410 --> 00:03:38.500
So it's carbon, carbon, carbon,

00:03:38.500 --> 00:03:41.760
carbon, carbon, carbon.

00:03:41.760 --> 00:03:45.780
And then each of these carbons
is bonded to three other

00:03:45.780 --> 00:03:48.850
atoms. It's bonded
to 1, 2 carbons.

00:03:48.850 --> 00:03:50.710
And it's also bonded
to a hydrogen.

00:03:50.710 --> 00:03:52.220
So let me draw the
hydrogens here.

00:03:52.220 --> 00:03:53.750
They're also bonded
to hydrogen.

00:03:53.750 --> 00:03:55.940
So this one will have a
hydrogen over here.

00:03:55.940 --> 00:03:57.850
This will have a hydrogen
over here.

00:03:57.850 --> 00:03:59.910
That will have a hydrogen
over there.

00:03:59.910 --> 00:04:02.000
That one has a hydrogen
over there.

00:04:02.000 --> 00:04:06.110
Hydrogen and hydrogen
right over there.

00:04:06.110 --> 00:04:09.990
So if we talk about
hybridization, we have three

00:04:09.990 --> 00:04:11.630
hybridized orbitals.

00:04:11.630 --> 00:04:14.910
This is sp2 hybridization.

00:04:14.910 --> 00:04:18.709
And each of these have a
leftover pi orbital that has

00:04:18.709 --> 00:04:19.709
not been hybridized.

00:04:19.709 --> 00:04:23.070
It's not directly bound to, or
that does not have a sigma

00:04:23.070 --> 00:04:25.720
bond to another atom.

00:04:25.720 --> 00:04:27.270
So you have these pi orbitals.

00:04:27.270 --> 00:04:30.070
You know, these pi orbitals
look like these dumbbells.

00:04:30.070 --> 00:04:32.280
So you have a pi orbital
over here.

00:04:32.280 --> 00:04:34.600
You have a pi orbital here.

00:04:34.600 --> 00:04:36.750
Pi orbital over here.

00:04:36.750 --> 00:04:39.570
Pi orbital over there.

00:04:39.570 --> 00:04:41.950
You have another pi orbital
over there.

00:04:41.950 --> 00:04:44.000
Pi orbital and pi orbital.

00:04:44.000 --> 00:04:45.850
And you know, pi orbital, I drew
them like this, because

00:04:45.850 --> 00:04:47.030
if I drew them bigger
than that, the

00:04:47.030 --> 00:04:48.430
diagram would get messy.

00:04:48.430 --> 00:04:51.830
But in general, whenever you
have double bonds, like this

00:04:51.830 --> 00:04:52.360
double bond.

00:04:52.360 --> 00:04:55.070
Let's say that this carbon--
let me change colors, so we

00:04:55.070 --> 00:04:56.000
know what we're focused on.

00:04:56.000 --> 00:04:58.450
So let's say this sigma bond
right over there, let's say

00:04:58.450 --> 00:05:02.110
that sigma bond right over
there, is this sigma bond.

00:05:02.110 --> 00:05:03.360
Actually let me do another
one, just so

00:05:03.360 --> 00:05:04.810
it's easier to see.

00:05:04.810 --> 00:05:09.000
Let's say that this sigma bond
right over here is this sigma

00:05:09.000 --> 00:05:11.790
bond, between these
two carbons.

00:05:11.790 --> 00:05:16.290
This double bond, the double
bond in blue, this one, or in

00:05:16.290 --> 00:05:19.020
purple right over there,
that's due to these

00:05:19.020 --> 00:05:21.180
overlapping pi orbitals.

00:05:21.180 --> 00:05:24.750
That carbon's pi orbitals and
that carbon's pi orbitals

00:05:24.750 --> 00:05:25.470
overlapping.

00:05:25.470 --> 00:05:27.580
I haven't drawn them
overlapping, but-- well,

00:05:27.580 --> 00:05:28.980
actually an electron
can really show up.

00:05:28.980 --> 00:05:30.310
It's all probabilistic anyway.

00:05:30.310 --> 00:05:32.390
But I could draw them big
enough, they would overlap,

00:05:32.390 --> 00:05:36.640
and these electrons would
form that extra pi bond.

00:05:36.640 --> 00:05:40.090
What happens in a conjugated
system of pi electrons.

00:05:40.090 --> 00:05:40.940
Let me write that down.

00:05:40.940 --> 00:05:42.770
It's just a very fancy word.

00:05:42.770 --> 00:05:54.598
Conjugated system
of pi electrons.

00:05:59.490 --> 00:06:01.350
These guys, at we see,
they could be

00:06:01.350 --> 00:06:02.710
bonded with each other.

00:06:02.710 --> 00:06:04.910
These guys could overlap.

00:06:04.910 --> 00:06:07.720
So there could be an overlap
going on over here.

00:06:07.720 --> 00:06:10.120
Or we could flip into this
configuration, where this guy

00:06:10.120 --> 00:06:12.280
would overlap with this
guy over here.

00:06:12.280 --> 00:06:15.610
And the reality is that these pi
electrons will actually be

00:06:15.610 --> 00:06:17.300
able to float around the ring.

00:06:17.300 --> 00:06:20.210
They'd actually be able to float
around all of these pi

00:06:20.210 --> 00:06:21.270
orbitals right over there.

00:06:21.270 --> 00:06:23.980
They'd actually be able to
float around the ring.

00:06:23.980 --> 00:06:26.300
So that's what people are really
talking about when they

00:06:26.300 --> 00:06:30.480
talk about aromatic compounds,
or aromaticity.

00:06:30.480 --> 00:06:34.070
That because of this, this is
a more stable compound.

00:06:34.070 --> 00:06:35.920
The most typical one that you're
going to see is a six

00:06:35.920 --> 00:06:39.470
carbon chain with three double
bonds, benzene, or things

00:06:39.470 --> 00:06:40.670
derived from them.

00:06:40.670 --> 00:06:42.490
But there actually are
more general ones.

00:06:42.490 --> 00:06:46.080
In general, you're going to see
anything that has 4n plus

00:06:46.080 --> 00:06:57.120
2 pi electrons in a cycle is
going to have aromaticity.

00:06:57.120 --> 00:07:03.190
Or is going to be an
aromatic compound.

00:07:03.190 --> 00:07:07.190
Let's just confirm this
actually makes it.

00:07:07.190 --> 00:07:10.140
Each of these guys over here
have one pi electron, even

00:07:10.140 --> 00:07:11.880
though this looks
like two bonds.

00:07:11.880 --> 00:07:15.750
Remember, this is one pi orbital
right over here.

00:07:15.750 --> 00:07:18.410
And you have one electron that's
going to be in this

00:07:18.410 --> 00:07:19.430
entire pi orbital.

00:07:19.430 --> 00:07:23.350
So this has one pi electron,
two, three, four, five, six.

00:07:23.350 --> 00:07:25.940
Another way to think about it,
each of these double bonds

00:07:25.940 --> 00:07:27.620
involves two pi electrons.

00:07:27.620 --> 00:07:32.190
So one, two, three,
four, five, six.

00:07:32.190 --> 00:07:35.450
So that follows what is
called Huckel's rule.

00:07:41.110 --> 00:07:43.070
I think there's two
dots above the u.

00:07:43.070 --> 00:07:44.880
Huckel's rule, maybe.

00:07:44.880 --> 00:07:46.600
That follows Huckel's rule.

00:07:46.600 --> 00:07:49.750
Because if you said n is
equal to 1, 4 times 1

00:07:49.750 --> 00:07:51.390
is 4 plus 2 is 6.

00:07:51.390 --> 00:07:53.210
So 6 pi electrons work.

00:07:53.210 --> 00:07:57.190
If n was 2, you'd have 4 times
2 plus 2, which is 10.

00:07:57.190 --> 00:07:59.650
So if you had 10 pi electrons,
it would also work.

00:07:59.650 --> 00:08:02.660
So a molecule that looks
like this-- let me see

00:08:02.660 --> 00:08:03.310
if I can draw it.

00:08:03.310 --> 00:08:05.920
A molecule that looks like
this would also work.

00:08:05.920 --> 00:08:13.750
So if you have one, two, three,
four, five, six, seven,

00:08:13.750 --> 00:08:19.640
eight, nine, ten, ten carbons.

00:08:19.640 --> 00:08:21.275
And then you had five
double bonds.

00:08:21.275 --> 00:08:27.760
So, one, two, three,
four, five.

00:08:27.760 --> 00:08:28.350
Just like that.

00:08:28.350 --> 00:08:30.290
You could imagine, these
guys could flip around.

00:08:30.290 --> 00:08:32.840
But this would also be
an aromatic compound.

00:08:32.840 --> 00:08:34.770
This has 10 pi electrons.

00:08:34.770 --> 00:08:36.870
Each of the carbons have
a pi electron.

00:08:36.870 --> 00:08:38.730
Or you could count the
pi electrons on each

00:08:38.730 --> 00:08:39.909
end of these pi bonds.

00:08:39.909 --> 00:08:47.800
One, two, three, four, five,
six, seven, eight, nine, ten.

00:08:47.800 --> 00:08:49.980
Now this is one thing that
I always wonder.

00:08:49.980 --> 00:08:51.470
It's like OK, it worked
with six.

00:08:51.470 --> 00:08:52.030
It worked with 10.

00:08:52.030 --> 00:08:52.750
But what about eight?

00:08:52.750 --> 00:08:55.760
It seems like with eight, maybe
these electrons, these

00:08:55.760 --> 00:08:58.210
double bonds, could flip
around just as easily.

00:08:58.210 --> 00:09:01.540
So what if I had, what if
I had-- or even four.

00:09:01.540 --> 00:09:03.860
What if I had a molecule
that looked like this?

00:09:03.860 --> 00:09:06.410
What if I had a molecule
that looked like this?

00:09:06.410 --> 00:09:09.770
Or a molecule that looked like
a stop sign-- so one, two,

00:09:09.770 --> 00:09:14.280
three, four, five, six, seven,
eight-- that had double bonds

00:09:14.280 --> 00:09:16.270
that alternated like this.

00:09:16.270 --> 00:09:18.230
You might say, hey,
maybe those also

00:09:18.230 --> 00:09:20.300
are aromatic compounds.

00:09:20.300 --> 00:09:22.500
Those also experience
aromaticity.

00:09:22.500 --> 00:09:25.010
Because couldn't this guy jump
around here, then that guy

00:09:25.010 --> 00:09:27.420
over there, and the electrons
cycle around.

00:09:27.420 --> 00:09:30.200
Or this guy jump over, these
electrons move there.

00:09:30.200 --> 00:09:31.010
Those move there.

00:09:31.010 --> 00:09:31.830
Those move there.

00:09:31.830 --> 00:09:33.210
And those move there.

00:09:33.210 --> 00:09:39.290
And it turns out that in these
compounds, the electrons do

00:09:39.290 --> 00:09:42.780
not, the pi electrons do not
stabilize the system.

00:09:42.780 --> 00:09:44.860
But this is actually less
stable than if it

00:09:44.860 --> 00:09:46.360
was not in a cycle.

00:09:46.360 --> 00:09:49.210
So actually this is-- these
right here, that don't follow

00:09:49.210 --> 00:09:50.310
the 4n plus 2.

00:09:50.310 --> 00:09:55.360
So 4n plus 2, you're talking
about 6, 10, 14 pi electrons.

00:09:55.360 --> 00:09:57.270
Which usually means
14 carbons, or 10

00:09:57.270 --> 00:09:59.290
carbons, or six carbons.

00:09:59.290 --> 00:10:02.090
The ones that don't follow them
but are still cyclical,

00:10:02.090 --> 00:10:04.150
and still have these alternating
bonds, these are

00:10:04.150 --> 00:10:05.400
called anti-aromatic.

00:10:11.380 --> 00:10:13.630
And are actually
very unstable.

00:10:13.630 --> 00:10:18.240
These are very, very unstable
and are more likely to break

00:10:18.240 --> 00:10:20.690
into a non-cycle.

00:10:20.690 --> 00:10:23.490
Anyway, hopefully you found
that vaguely useful.


Ether naming and introduction

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:03.240
We've already touched on ethers
in several videos.

00:00:03.240 --> 00:00:07.080
They've been our useful aprotic
solvent in several of

00:00:07.080 --> 00:00:07.800
our reactions.

00:00:07.800 --> 00:00:10.130
But I thought it was about time
that we actually devoted

00:00:10.130 --> 00:00:12.460
a video or two to ethers.

00:00:12.460 --> 00:00:14.820
And like all things that we've
done in organic chemistry, a

00:00:14.820 --> 00:00:17.950
good way to familiarize
ourselves with the molecules

00:00:17.950 --> 00:00:20.210
and how they look, is to
actually name them.

00:00:20.210 --> 00:00:21.130
So let's do a couple.

00:00:21.130 --> 00:00:23.280
And the first few you've
seen already.

00:00:23.280 --> 00:00:28.210
So let's say we have this
molecule right here.

00:00:28.210 --> 00:00:29.640
What I'm going to do is I'm
going to teach you two

00:00:29.640 --> 00:00:30.430
ways to name it.

00:00:30.430 --> 00:00:32.740
The common name, and that's
probably the more important

00:00:32.740 --> 00:00:34.270
one, especially with ethers.

00:00:34.270 --> 00:00:36.860
Because, as you could imagine,
that is the more common name.

00:00:36.860 --> 00:00:38.050
That is what people say.

00:00:38.050 --> 00:00:39.940
And then I'll also show
you how to name it

00:00:39.940 --> 00:00:42.350
using the IUPAC name.

00:00:42.350 --> 00:00:44.140
So let me write this down.

00:00:44.140 --> 00:00:50.950
IUPAC name, which is the
International Union of Pure

00:00:50.950 --> 00:00:52.490
and Applied Chemistry.

00:00:52.490 --> 00:00:55.420
And they've come up with kind
of the official naming

00:00:55.420 --> 00:00:58.410
protocols for all of these
organic molecules.

00:00:58.410 --> 00:01:00.070
This is actually the convention
that we used

00:01:00.070 --> 00:01:03.260
earlier when we did the alkanes
and the alkenes.

00:01:03.260 --> 00:01:06.420
But in the case of ethers, the
common name is more common.

00:01:06.420 --> 00:01:09.280
So the common name for this
molecule right here.

00:01:09.280 --> 00:01:11.350
You look at the two carbon
groups here.

00:01:11.350 --> 00:01:11.770
So let's see.

00:01:11.770 --> 00:01:13.630
You have this one right here.

00:01:13.630 --> 00:01:15.900
That is an ethyl group.

00:01:15.900 --> 00:01:17.190
That's an ethyl group
right there.

00:01:17.190 --> 00:01:19.010
You have one, two carbons.

00:01:19.010 --> 00:01:21.910
And then you look at the other
carbon group right over there.

00:01:21.910 --> 00:01:23.280
That's also an ethyl group.

00:01:23.280 --> 00:01:25.340
You have one, two carbons.

00:01:25.340 --> 00:01:28.250
So you call this-- let me just
write this down-- that is also

00:01:28.250 --> 00:01:29.000
an ethyl group.

00:01:29.000 --> 00:01:34.075
So the common name for this
is just diethyl ether.

00:01:38.820 --> 00:01:41.610
And the ether tells you, this
part tells you, that you have

00:01:41.610 --> 00:01:44.600
an oxygen in between your
two ethyl groups.

00:01:44.600 --> 00:01:46.085
This is the common name.

00:01:50.460 --> 00:01:54.710
Now the International Union of
Pure and Applied Chemistry

00:01:54.710 --> 00:01:56.290
official name for it.

00:01:56.290 --> 00:01:58.870
You kind of do something similar
to how we named other

00:01:58.870 --> 00:01:59.450
things before.

00:01:59.450 --> 00:02:01.260
You look for the
longest chain.

00:02:01.260 --> 00:02:02.940
Let me redraw it.

00:02:02.940 --> 00:02:05.280
So maybe on the left hand side
I'll do the common names.

00:02:05.280 --> 00:02:08.669
On the right hand side I'll
do the IUPAC names.

00:02:08.669 --> 00:02:11.630
So let me redraw what
the common name

00:02:11.630 --> 00:02:13.010
of the diethyl ether.

00:02:13.010 --> 00:02:14.520
You look for the
longest chain.

00:02:14.520 --> 00:02:16.580
In this case, there's
two longest chains.

00:02:16.580 --> 00:02:18.980
There's this one that has
one, two carbons.

00:02:18.980 --> 00:02:21.260
And then you have this one,
that has one, two carbons.

00:02:21.260 --> 00:02:22.590
So you can pick either one.

00:02:22.590 --> 00:02:27.450
I'll just pick this one as the
main chain right over there.

00:02:27.450 --> 00:02:31.180
It has two carbons,
no double bonds.

00:02:31.180 --> 00:02:32.430
It is an ethane.

00:02:35.640 --> 00:02:41.870
And then you say, OK, I have
this alkoxy group.

00:02:41.870 --> 00:02:44.820
We put the oxy at the end of it
because it has this oxygen

00:02:44.820 --> 00:02:45.530
right here.

00:02:45.530 --> 00:02:50.330
But it's the alk part of it
has two carbons, one, two.

00:02:50.330 --> 00:02:53.360
So we call this right here,
we call this ethoxy.

00:02:55.940 --> 00:02:59.190
So one other way to name this,
we have this ethoxy group

00:02:59.190 --> 00:03:01.390
attached to the one carbon.

00:03:01.390 --> 00:03:03.490
We're just going to start
numbering on this side of the

00:03:03.490 --> 00:03:05.910
ethane, just because that's
where the group is, attached

00:03:05.910 --> 00:03:07.070
to the one carbon.

00:03:07.070 --> 00:03:08.390
So we call this 1-ethoxyethane.

00:03:15.200 --> 00:03:18.120
You'll almost never see it
actually named this way, even

00:03:18.120 --> 00:03:19.860
though this is the
official name.

00:03:19.860 --> 00:03:22.840
You're much more likely to see
this as diethyl ether.

00:03:22.840 --> 00:03:25.140
And at least in my brain, this
resonates a lot more.

00:03:25.140 --> 00:03:26.920
You just say what are
the two groups.

00:03:26.920 --> 00:03:28.080
And you throw the
ether at end.

00:03:28.080 --> 00:03:30.130
You know that there's an
oxygen in between.

00:03:30.130 --> 00:03:31.870
Let's do a couple
more of these.

00:03:31.870 --> 00:03:34.990
So let's say I have this
molecule right here.

00:03:34.990 --> 00:03:38.810
I have this molecule
right over here.

00:03:38.810 --> 00:03:41.490
The common way is you look at
the two groups on either side

00:03:41.490 --> 00:03:43.010
of the oxygen.

00:03:43.010 --> 00:03:47.260
So this right here-- let me do
this in a different color--

00:03:47.260 --> 00:03:49.810
this group on the left
right here, we have

00:03:49.810 --> 00:03:51.830
one, two, three carbons.

00:03:51.830 --> 00:03:53.610
It's a propyl group,
but we're attached

00:03:53.610 --> 00:03:54.580
to that middle carbon.

00:03:54.580 --> 00:03:56.190
So this is an isopropyl group.

00:04:00.550 --> 00:04:02.170
And on the right hand
side right here, we

00:04:02.170 --> 00:04:03.560
just have one carbon.

00:04:03.560 --> 00:04:07.780
So this is right here-- I keep
using that blue-- this right

00:04:07.780 --> 00:04:12.820
here, this is a methyl group.

00:04:12.820 --> 00:04:15.470
So the common way of naming
it, you just list both of

00:04:15.470 --> 00:04:16.880
these groups and then
you write ether.

00:04:16.880 --> 00:04:18.730
And you list them in
alphabetical order.

00:04:18.730 --> 00:04:20.560
I comes before m.

00:04:20.560 --> 00:04:32.703
So this is, the common name
is isopropyl methyl ether.

00:04:36.890 --> 00:04:41.140
Now if we were to do the IUPAC
naming, we look for the

00:04:41.140 --> 00:04:42.310
longest carbon chain.

00:04:42.310 --> 00:04:45.110
Let me redraw the
molecule itself.

00:04:45.110 --> 00:04:48.380
So let me redraw the same
thing right there.

00:04:48.380 --> 00:04:50.880
So what's the longest
carbon chain here?

00:04:50.880 --> 00:04:53.660
Well we have one, two, three
carbons right there.

00:04:53.660 --> 00:04:55.300
We only have one carbon
right there.

00:04:55.300 --> 00:04:59.020
So this thing right here is
our longest carbon chain.

00:04:59.020 --> 00:05:02.950
It has three carbons on it, and
it had no double bonds.

00:05:02.950 --> 00:05:06.610
So eth, meth, prop, propyl,
or it's actually propane.

00:05:06.610 --> 00:05:10.120
So this is our longest. So we
write propane right there,

00:05:10.120 --> 00:05:13.130
because we're using the IUPAC
naming mechanism.

00:05:13.130 --> 00:05:17.110
And then we look at this methoxy
group right here.

00:05:17.110 --> 00:05:19.740
And I call this a methoxy group,
because I have the o.

00:05:19.740 --> 00:05:20.860
That gives us the oxy.

00:05:20.860 --> 00:05:23.200
And I just have a methyl
group right here.

00:05:23.200 --> 00:05:24.450
So this is methoxy.

00:05:26.530 --> 00:05:30.090
You remember that meth is the
prefix for just having only

00:05:30.090 --> 00:05:30.920
one carbon.

00:05:30.920 --> 00:05:32.950
We add the oxy because
that oxygen is there.

00:05:32.950 --> 00:05:37.010
And it's attached to the two
carbons on the propane chain,

00:05:37.010 --> 00:05:39.190
no matter what direction you
start naming from, or

00:05:39.190 --> 00:05:39.870
numbering from.

00:05:39.870 --> 00:05:42.390
One, two, three.

00:05:42.390 --> 00:05:43.640
So this is 2-methoxypropane.

00:05:51.300 --> 00:05:52.120
Let's do another one.

00:05:52.120 --> 00:05:52.940
Let's do one more.

00:05:52.940 --> 00:05:55.620
And I think you'll get the
gist of at least the

00:05:55.620 --> 00:05:59.070
reasonably simple
ethers to name.

00:05:59.070 --> 00:06:05.090
So let's put a ring
over there.

00:06:05.090 --> 00:06:07.620
And then that's attached
to an oxygen.

00:06:07.620 --> 00:06:10.640
And then we have another carbon
chain right here.

00:06:10.640 --> 00:06:12.610
And then we have another carbon
chain right there.

00:06:12.610 --> 00:06:14.360
Let me just copy and paste
that so that I don't

00:06:14.360 --> 00:06:16.110
have to redraw it.

00:06:16.110 --> 00:06:19.080
So let me copy and paste.

00:06:19.080 --> 00:06:20.090
All right.

00:06:20.090 --> 00:06:23.050
So let's do the common name
first. That always tends to be

00:06:23.050 --> 00:06:25.220
a little bit more fun.

00:06:25.220 --> 00:06:29.780
So on this side, we have one,
two, three, four, five, six

00:06:29.780 --> 00:06:31.850
carbons in a cycle.

00:06:31.850 --> 00:06:34.620
This right here on the
left hand side is

00:06:34.620 --> 00:06:36.190
a cyclohexyl group.

00:06:40.080 --> 00:06:44.910
This on the right hand side,
we have one, two, three.

00:06:44.910 --> 00:06:47.380
This is just a straight-up
propyl group.

00:06:50.960 --> 00:06:52.970
And so when you name the ether,
you just put these two

00:06:52.970 --> 00:06:55.050
groups in alphabetical
order, and you add an

00:06:55.050 --> 00:06:55.990
ether at the end.

00:06:55.990 --> 00:06:57.470
So it's cyclohexyl.

00:06:57.470 --> 00:06:59.570
C comes before p.

00:06:59.570 --> 00:07:04.670
So it's cyclohexyl propyl.

00:07:04.670 --> 00:07:06.860
Let me get that shade
of yellow right.

00:07:06.860 --> 00:07:09.750
Cyclohexyl propyl ether.

00:07:13.580 --> 00:07:16.670
Now let's do the IUPAC
way to name it.

00:07:16.670 --> 00:07:18.870
So you look for the longest
carbon chain here.

00:07:18.870 --> 00:07:22.090
In this case, it's going to be
the cyclohexane right here.

00:07:22.090 --> 00:07:26.540
We have one, two, three, four,
five, six carbons there.

00:07:26.540 --> 00:07:29.310
We only have one, two,
three there.

00:07:29.310 --> 00:07:32.020
So this is kind of
our backbone.

00:07:32.020 --> 00:07:33.370
So we write down cyclohexane.

00:07:36.950 --> 00:07:39.080
No double bonds, so
it's a hexane.

00:07:39.080 --> 00:07:41.410
So that's the cyclohexane
right there.

00:07:41.410 --> 00:07:46.920
If you just had these three
carbons, it would be a propyl.

00:07:46.920 --> 00:07:49.170
But this is not just
three carbons.

00:07:49.170 --> 00:07:51.020
It's three carbons and
then an oxygen.

00:07:51.020 --> 00:07:54.200
So we would call it a propoxy.

00:07:54.200 --> 00:07:55.920
So this is propoxy group.

00:07:58.890 --> 00:08:00.710
And you don't have to number
it because it can just be

00:08:00.710 --> 00:08:02.080
attached to any of
these carbons.

00:08:02.080 --> 00:08:03.670
It would essentially be
the same molecule.

00:08:03.670 --> 00:08:05.930
So you can just call this
propoxy cyclohexane.

00:08:09.790 --> 00:08:13.160
Let me make it a little bit
closer to the cyclohexane.

00:08:13.160 --> 00:08:18.750
Propoxy cyclohexane.

00:08:18.750 --> 00:08:21.020
But once again the common
name is what you're

00:08:21.020 --> 00:08:21.980
more likely to see.

00:08:21.980 --> 00:08:23.990
Now that we've named a few of
them, let's think a little bit

00:08:23.990 --> 00:08:25.660
about their properties.

00:08:25.660 --> 00:08:28.680
What we've seen already is
that-- and we've used it

00:08:28.680 --> 00:08:31.180
several times, especially in our
Sn2 reactions and things

00:08:31.180 --> 00:08:33.960
like that-- places where
we didn't want

00:08:33.960 --> 00:08:35.120
protons floating around.

00:08:35.120 --> 00:08:37.559
We used actually
diethyl ether.

00:08:37.559 --> 00:08:40.760
And in general ethers do
make for good solvents.

00:08:40.760 --> 00:08:43.409
They tend to be fairly
unreactive.

00:08:43.409 --> 00:08:46.140
So good solvents.

00:08:46.140 --> 00:08:49.160
Especially when you're looking
for an aprotic solvent.

00:08:49.160 --> 00:08:52.060
Remember, aprotic means you
don't have hydrogens that can

00:08:52.060 --> 00:08:56.710
kind of lose their electron to
maybe an electronegative atom

00:08:56.710 --> 00:08:57.640
like an oxygen.

00:08:57.640 --> 00:09:00.395
And then the proton just floats
around, and then can go

00:09:00.395 --> 00:09:02.450
and react with other things.

00:09:02.450 --> 00:09:04.865
This does not have any hydrogens
directly bonded to

00:09:04.865 --> 00:09:06.980
an oxygen in any
of these cases.

00:09:06.980 --> 00:09:09.500
So it is an aprotic solvent.

00:09:09.500 --> 00:09:11.930
And because it doesn't have any
hydrogens bonded to the

00:09:11.930 --> 00:09:14.670
oxygen, you also have
no hydrogen bonding.

00:09:14.670 --> 00:09:17.970
And just as a bit of a review,
you know that in water you

00:09:17.970 --> 00:09:21.740
have the situation-- let me draw
some water molecules-- in

00:09:21.740 --> 00:09:25.400
water you have the situation
where the

00:09:25.400 --> 00:09:26.610
oxygen hogs the electrons.

00:09:26.610 --> 00:09:28.630
So it has a partial
negative charge.

00:09:28.630 --> 00:09:33.830
Hydrogen gets its electrons
hogged or taken away, or it

00:09:33.830 --> 00:09:34.860
spends less time with them.

00:09:34.860 --> 00:09:36.550
So it has a partial
positive charge.

00:09:36.550 --> 00:09:39.130
So this oxygen will have a
partial negative charge.

00:09:39.130 --> 00:09:42.520
And so the hydrogens with the
partial positive charge are

00:09:42.520 --> 00:09:45.260
attracted to the oxygens with
the partial negative charge.

00:09:45.260 --> 00:09:47.000
And you have this hydrogen
bonding.

00:09:47.000 --> 00:09:51.220
And this hydrogen bonding
makes water.

00:09:51.220 --> 00:09:52.710
It pulls the molecules
together.

00:09:52.710 --> 00:09:57.080
So you need to put more energy
into it for it to either melt,

00:09:57.080 --> 00:09:59.015
or for it to actually boil.

00:09:59.015 --> 00:10:01.260
And for the molecules to
kind of get ripped

00:10:01.260 --> 00:10:02.440
away from each other.

00:10:02.440 --> 00:10:04.120
And that's also true
with alcohols.

00:10:04.120 --> 00:10:06.990
Alcohols only have one hydrogen
to each oxygen, but

00:10:06.990 --> 00:10:10.640
they still have the hydrogen
bonding going on.

00:10:10.640 --> 00:10:14.390
In the case of ethers, there
is no hydrogen bonding.

00:10:14.390 --> 00:10:16.060
I'll represent each of
the carbon chains

00:10:16.060 --> 00:10:17.740
with an R and an R.

00:10:17.740 --> 00:10:20.820
I'll write R prime right here
to show that it could be a

00:10:20.820 --> 00:10:23.680
different carbon chain
than this right here.

00:10:23.680 --> 00:10:25.400
And the R stands for radical.

00:10:25.400 --> 00:10:27.410
Not to be confused with
free radical.

00:10:27.410 --> 00:10:29.090
Completely different things.

00:10:29.090 --> 00:10:31.470
This R just means really
a carbon chain

00:10:31.470 --> 00:10:32.535
attached to this oxygen.

00:10:32.535 --> 00:10:37.890
But here there's no hydrogen
getting its electrons hogged

00:10:37.890 --> 00:10:39.730
by oxygens with partial
positive and

00:10:39.730 --> 00:10:41.060
partial negative charges.

00:10:41.060 --> 00:10:44.570
So you're not going to have that
type of hydrogen bonding.

00:10:44.570 --> 00:10:49.380
And because of that, ethers have
much lower melting and

00:10:49.380 --> 00:10:50.170
boiling points.

00:10:50.170 --> 00:10:50.960
It's much easier.

00:10:50.960 --> 00:10:53.430
You have to put less heat into
the system for these molecules

00:10:53.430 --> 00:10:56.260
to break away from each other,
because they aren't attracted

00:10:56.260 --> 00:10:57.510
to each other as much.


Resonance

WEBVTT
Kind: captions
Language: en

00:00:00.710 --> 00:00:03.530
I'm going to draw a molecule
of benzene.

00:00:03.530 --> 00:00:06.340
And then we're going to think
about if anything interesting

00:00:06.340 --> 00:00:07.550
might happen with
that molecule.

00:00:07.550 --> 00:00:09.140
So let me draw it.

00:00:09.140 --> 00:00:12.680
So we have 6 carbons
in a ring.

00:00:12.680 --> 00:00:22.290
1, 2, 3, 4, 5 and 6
carbons in a ring.

00:00:22.290 --> 00:00:25.030
What's interesting about
benzene, why it's different

00:00:25.030 --> 00:00:28.320
than cyclohexane, is that
it has these 3 double

00:00:28.320 --> 00:00:29.520
bonds in the ring.

00:00:29.520 --> 00:00:32.400
So let's say we have these two
carbons are double bonded to

00:00:32.400 --> 00:00:36.150
each other, these two carbons
are double bonded, and then

00:00:36.150 --> 00:00:39.630
these two carbons over here
are double bonded.

00:00:39.630 --> 00:00:41.550
Actually, I'll draw the
hydrogens here just so that we

00:00:41.550 --> 00:00:43.050
remember that they're there.

00:00:43.050 --> 00:00:44.930
But I'll it in a subtle color.

00:00:44.930 --> 00:00:46.960
So this carbon right
here is going to be

00:00:46.960 --> 00:00:48.320
bonded to how many hydrogens?

00:00:48.320 --> 00:00:51.880
It has 1, 2, 3 valence electrons
already used up.

00:00:51.880 --> 00:00:55.390
So it's going to have one
bonded to one hydrogen.

00:00:55.390 --> 00:00:57.080
This one right here,
same thing.

00:00:57.080 --> 00:00:59.050
Bonded to one hydrogen.

00:00:59.050 --> 00:01:01.400
So it has 4 valence electrons.

00:01:01.400 --> 00:01:02.380
This one, same thing.

00:01:02.380 --> 00:01:03.350
I think you see the pattern.

00:01:03.350 --> 00:01:07.180
That each of these are-- they
have three bonds to carbons,

00:01:07.180 --> 00:01:09.770
one single bond to two carbons,
and then one extra

00:01:09.770 --> 00:01:10.390
double bond.

00:01:10.390 --> 00:01:11.890
And then the fourth bond
is to hydrogen.

00:01:11.890 --> 00:01:14.040
So let me just draw all
of the hydrogens here.

00:01:14.040 --> 00:01:16.420
I'm doing it in this dark color
so we don't have to pay

00:01:16.420 --> 00:01:17.950
too much attention to it.

00:01:17.950 --> 00:01:19.770
Now this right here,
this is benzine.

00:01:19.770 --> 00:01:23.310
And you're going to see a lot
about benzine in the future.

00:01:23.310 --> 00:01:26.910
But in this video, we're going
to study or try to understand

00:01:26.910 --> 00:01:30.110
a particularly interesting
property of benzene, and

00:01:30.110 --> 00:01:31.360
that's resonance.

00:01:35.720 --> 00:01:38.520
And it's not a property of just
benzene, it's a property

00:01:38.520 --> 00:01:40.150
of many organic molecules.

00:01:40.150 --> 00:01:43.350
But benzene is kind of
the most fun version.

00:01:43.350 --> 00:01:45.940
So let's think about what
might happen with this

00:01:45.940 --> 00:01:47.370
molecule right here.

00:01:47.370 --> 00:01:50.980
So I have this electron.

00:01:50.980 --> 00:01:52.870
Let me do that in a
different color.

00:01:52.870 --> 00:01:56.240
I have this-- let me
do it in this blue.

00:01:56.240 --> 00:01:58.570
I have this electron
over here.

00:01:58.570 --> 00:02:03.140
What if this electron moved over
to this carbon over here?

00:02:03.140 --> 00:02:05.110
So this carbon is still going
to have the other

00:02:05.110 --> 00:02:06.110
electron in the bond.

00:02:06.110 --> 00:02:08.270
It's just going to kind of pivot
around a little bit.

00:02:08.270 --> 00:02:10.259
So that electron moves
over there.

00:02:10.259 --> 00:02:14.280
Now this carbon doesn't need 5
electrons, so this electron

00:02:14.280 --> 00:02:17.170
goes to that carbon
right over there.

00:02:17.170 --> 00:02:22.160
Now this carbon doesn't need 5
electrons, so that electron

00:02:22.160 --> 00:02:24.850
goes back to the original
carbon that

00:02:24.850 --> 00:02:26.210
lost that first electron.

00:02:26.210 --> 00:02:28.160
So at the end of the
day, everyone has

00:02:28.160 --> 00:02:30.800
kind of broken even.

00:02:30.800 --> 00:02:36.390
If this happened, we might
end up with a structure

00:02:36.390 --> 00:02:38.140
that looks like this.

00:02:38.140 --> 00:02:42.360
And I'll draw a two-way arrow
because we can actually go in

00:02:42.360 --> 00:02:43.880
both directions.

00:02:43.880 --> 00:02:45.940
So let me draw just
the carbon chain.

00:02:45.940 --> 00:02:53.790
So 1 carbon, 2 carbons, 3
carbons, 4 carbons, 5 carbons

00:02:53.790 --> 00:02:55.620
and 6 carbons.

00:02:55.620 --> 00:02:59.710
And then, over here, we had the
double bond over here, but

00:02:59.710 --> 00:03:00.910
now it's moved over here.

00:03:00.910 --> 00:03:03.380
So now the double bond-- and
actually, let me do it in a

00:03:03.380 --> 00:03:05.070
blue color so we see
the difference.

00:03:05.070 --> 00:03:07.100
So now the double bond
is over here.

00:03:07.100 --> 00:03:09.750
This blue electron has
moved over there.

00:03:09.750 --> 00:03:12.260
This blue electron has
moved up here.

00:03:12.260 --> 00:03:14.040
Actually, let me color code it,
so it makes it very clear.

00:03:14.040 --> 00:03:16.190
So let's say this is
a green electron.

00:03:16.190 --> 00:03:20.100
Now the green electron has moved
from this carbon over to

00:03:20.100 --> 00:03:20.630
that carbon.

00:03:20.630 --> 00:03:22.960
We can imagine that
it's done that.

00:03:22.960 --> 00:03:26.670
Then you would have this magenta
carbon or this magenta

00:03:26.670 --> 00:03:29.290
electron that was with this
carbon, but now it's moved

00:03:29.290 --> 00:03:31.390
over to this carbon over here.

00:03:31.390 --> 00:03:34.540
And now the double bond
has shifted as well.

00:03:34.540 --> 00:03:36.030
That's what this arrow showed.

00:03:38.740 --> 00:03:40.850
We'll stick with the blue
carbon over there.

00:03:40.850 --> 00:03:43.750
That blue carbon has moved down
to the original carbon.

00:03:43.750 --> 00:03:46.015
And now the double bond
has shifted over here.

00:03:48.930 --> 00:03:52.600
So we essentially have a very
similar, really, a very

00:03:52.600 --> 00:03:54.100
similar molecule.

00:03:54.100 --> 00:03:56.160
This is actually just a rotated
version of that.

00:03:56.160 --> 00:03:59.320
But we have these double bonds
that could keep flipping back

00:03:59.320 --> 00:04:02.140
and forth between this position
and that position

00:04:02.140 --> 00:04:02.410
over there.

00:04:02.410 --> 00:04:03.930
They can just keep
on doing it.

00:04:03.930 --> 00:04:06.440
They can just keep flipping
either backwards or forwards.

00:04:06.440 --> 00:04:10.560
And the reality of benzene is
that it's actually never in

00:04:10.560 --> 00:04:13.090
either this structure
or this structure.

00:04:13.090 --> 00:04:17.019
It's always, actually, in
something right in between.

00:04:17.019 --> 00:04:19.110
The reality of benzene
actually looks

00:04:19.110 --> 00:04:21.050
something more like this.

00:04:21.050 --> 00:04:24.160
And I'll just draw it without
drawing all the carbons and

00:04:24.160 --> 00:04:26.800
the hydrogens.

00:04:26.800 --> 00:04:29.100
And obviously, in this case, let
me draw the hydrogens here

00:04:29.100 --> 00:04:30.410
since I drew the hydrogens
up here.

00:04:30.410 --> 00:04:32.700
This had the hydrogens
over here.

00:04:32.700 --> 00:04:33.700
Don't want to forget those.

00:04:33.700 --> 00:04:35.585
If you ever forget them
they're implicit.

00:04:35.585 --> 00:04:37.670
I want to draw the hydrogens.

00:04:37.670 --> 00:04:39.970
But if we just look at the
overall ring, we know that the

00:04:39.970 --> 00:04:41.790
carbons and the hydrogens
are implicit.

00:04:41.790 --> 00:04:44.650
The actual structure of benzene
is actually in between

00:04:44.650 --> 00:04:45.920
that and that.

00:04:45.920 --> 00:04:49.490
In reality, you kind of have a
half double bond between all

00:04:49.490 --> 00:04:50.720
of the carbons.

00:04:50.720 --> 00:04:54.240
So the reality is, is that it
looks something like this.

00:04:54.240 --> 00:04:57.830
So you have half a double bond
there, half a double bond

00:04:57.830 --> 00:05:02.670
there, half a double bond over
here, half a double bond over

00:05:02.670 --> 00:05:06.400
here, and then half a double
bond over here.

00:05:06.400 --> 00:05:07.900
And then we're almost done.

00:05:07.900 --> 00:05:10.250
And then, half a double
bond over here.

00:05:10.250 --> 00:05:13.900
The reality of benzene is that
these electrons are actually

00:05:13.900 --> 00:05:15.360
spinning around the
whole ring.

00:05:15.360 --> 00:05:16.920
It's not flip-flopping
between this

00:05:16.920 --> 00:05:18.260
structure and this structure.

00:05:18.260 --> 00:05:21.220
The actual structure, the lower
energy state structure,

00:05:21.220 --> 00:05:22.510
is this right here.

00:05:22.510 --> 00:05:25.040
Now these Lewis diagrams or
actually, I haven't drawn all

00:05:25.040 --> 00:05:25.850
of the Lewis electrons.

00:05:25.850 --> 00:05:28.510
But these are considered
contributing structures.

00:05:28.510 --> 00:05:30.650
And you often draw these when
you're doing reaction

00:05:30.650 --> 00:05:33.600
mechanisms. But the reality
is, is that resonance, the

00:05:33.600 --> 00:05:36.450
resonance of these positions
creates-- the reality of

00:05:36.450 --> 00:05:38.120
benzene is that it's actually
sitting in this

00:05:38.120 --> 00:05:40.230
intermediate position.

00:05:40.230 --> 00:05:43.600
Now, this doesn't happen
only with benzene.

00:05:43.600 --> 00:05:45.590
Another example, there's going
to be many examples.

00:05:45.590 --> 00:05:48.840
But just so that we're familiar
with maybe two of the

00:05:48.840 --> 00:05:52.130
best examples, another example
that you'll see a lot in the

00:05:52.130 --> 00:05:55.270
context of resonance is
the carbonate ion.

00:05:55.270 --> 00:05:56.460
So carbonate ion.

00:05:56.460 --> 00:05:59.670
You have a double bond to one
oxygen and then you have

00:05:59.670 --> 00:06:01.980
single bonds to two
other oxygens.

00:06:01.980 --> 00:06:05.240
And those two other oxygens
have extra electrons.

00:06:05.240 --> 00:06:12.070
So if I were to draw this oxygen
over here it has 1, 2,

00:06:12.070 --> 00:06:16.980
3, 4, 5, 6 valence-- or
actually, I should

00:06:16.980 --> 00:06:17.930
say, it has 7 valence.

00:06:17.930 --> 00:06:19.150
Let me make it very clear.

00:06:19.150 --> 00:06:24.800
So it has 1, 2, 3, 4, 5,
6, 7 valence electrons.

00:06:24.800 --> 00:06:29.140
It has one extra electron, so
it has a negative charge.

00:06:29.140 --> 00:06:30.480
And the same is true
for this one.

00:06:30.480 --> 00:06:37.220
It has 1, 2, 3, 4, 5, 6,
7 valence electrons.

00:06:37.220 --> 00:06:37.800
One extra.

00:06:37.800 --> 00:06:40.030
So it has a negative charge.

00:06:40.030 --> 00:06:42.330
If you were to just look at
this, I guess you could call

00:06:42.330 --> 00:06:45.420
it this resonance structure or
this contributing structure,

00:06:45.420 --> 00:06:48.330
you'd say hey, maybe this
oxygen-- and this oxygen here

00:06:48.330 --> 00:06:51.120
is neutral, so it has
6 valence electrons.

00:06:51.120 --> 00:06:56.980
1, 2, 3, 4, 5, 6.

00:06:56.980 --> 00:07:01.230
Maybe, just maybe, one of these
electrons can be given

00:07:01.230 --> 00:07:04.180
to the carbon and then the
carbon would lose an electron

00:07:04.180 --> 00:07:05.740
to this guy on top.

00:07:05.740 --> 00:07:12.290
So maybe you could imagine a
situation where this electron

00:07:12.290 --> 00:07:17.720
right here gets given
to the carbon.

00:07:17.720 --> 00:07:20.430
And when that gets given to
the carbon, the carbon

00:07:20.430 --> 00:07:23.950
releases-- it all happen
simultaneously.

00:07:23.950 --> 00:07:27.460
The carbon releases this
electron and it goes back up

00:07:27.460 --> 00:07:28.910
to that oxygen over there.

00:07:28.910 --> 00:07:30.340
And so what's that going
to look like if

00:07:30.340 --> 00:07:31.630
that were to happen?

00:07:31.630 --> 00:07:34.550
So if that were to happen,
now our structure

00:07:34.550 --> 00:07:35.920
will look like this.

00:07:35.920 --> 00:07:37.200
We have a carbon.

00:07:37.200 --> 00:07:40.820
Now this carbon only has
a single bond up here.

00:07:40.820 --> 00:07:42.520
And then we have our oxygen.

00:07:42.520 --> 00:07:46.090
The oxygen, it had its
6 valence electrons.

00:07:46.090 --> 00:07:52.420
1, 2, 3, 4, 5, 6 valence
electrons.

00:07:52.420 --> 00:07:55.320
But now it got this
extra blue one.

00:07:55.320 --> 00:07:58.590
And now it got this extra blue
one, so now it has 7 valence

00:07:58.590 --> 00:08:02.280
electrons, and it has
a negative charge.

00:08:02.280 --> 00:08:04.230
Now this oxygen over here
gave one of its

00:08:04.230 --> 00:08:05.150
electrons to the carbon.

00:08:05.150 --> 00:08:07.050
Now it is bonded with it.

00:08:07.050 --> 00:08:09.030
So now the carbon has
a double bond.

00:08:09.030 --> 00:08:10.750
I'll actually do it
in that color.

00:08:10.750 --> 00:08:14.320
Has a double bond with this
oxygen down here.

00:08:14.320 --> 00:08:18.230
It gave an electron, so now it
only has 6 valence electrons.

00:08:18.230 --> 00:08:21.940
1, 2, 3, 4, 5, 6.

00:08:21.940 --> 00:08:23.040
And it is now neutral.

00:08:23.040 --> 00:08:25.220
And this oxygen over here,
nothing really

00:08:25.220 --> 00:08:26.280
new happened to it.

00:08:26.280 --> 00:08:28.540
I could just copy
and paste it.

00:08:28.540 --> 00:08:31.020
So let me copy and then
let me paste it.

00:08:31.020 --> 00:08:33.799
So this one is just sitting
right like that.

00:08:33.799 --> 00:08:41.650
But you could imagine a
situation where this oxygen

00:08:41.650 --> 00:08:43.799
right here, then all of a
sudden-- and it could have

00:08:43.799 --> 00:08:46.350
come from this oxygen up here
or it could come from this

00:08:46.350 --> 00:08:47.520
oxygen right here.

00:08:47.520 --> 00:08:49.450
This oxygen says hey, I have
an extra electron.

00:08:49.450 --> 00:08:50.670
Let me give it to the carbon.

00:08:50.670 --> 00:08:53.280
And then the carbon releases a
double bond with one of the

00:08:53.280 --> 00:08:54.210
other oxygens.

00:08:54.210 --> 00:08:57.080
In this case, it would
be this one.

00:08:57.080 --> 00:08:57.940
Let me draw it.

00:08:57.940 --> 00:09:01.810
So maybe this electron right
here gets given to the carbon.

00:09:01.810 --> 00:09:03.150
Forms a double bond.

00:09:03.150 --> 00:09:05.630
Then the carbon can let
go of an electron.

00:09:05.630 --> 00:09:10.260
And so this electron right here
goes back to this oxygen.

00:09:10.260 --> 00:09:11.780
And so what happens?

00:09:11.780 --> 00:09:15.190
So if that were to happen, our
structure looks like this.

00:09:15.190 --> 00:09:20.120
We have a carbon single bonded
to an oxygen up here that has

00:09:20.120 --> 00:09:24.770
1, 2, 3, 4, 5, 6, 7
valence electrons.

00:09:24.770 --> 00:09:27.730
That hasn't changed in-- we
could call it this resonance

00:09:27.730 --> 00:09:29.110
reaction, or however you
want to call it.

00:09:29.110 --> 00:09:31.420
So it still has a
negative charge.

00:09:31.420 --> 00:09:33.100
We have this guy down here.

00:09:33.100 --> 00:09:34.640
He took his electron back.

00:09:34.640 --> 00:09:37.270
So now he has 7 valence
electrons again.

00:09:37.270 --> 00:09:43.970
So 1, 2, 3, 4, 5, 6, 7 valence
electrons again.

00:09:43.970 --> 00:09:45.760
And I can even show the
one that he got back.

00:09:45.760 --> 00:09:47.220
That one's in purple.

00:09:47.220 --> 00:09:48.870
So he now has a negative
charge.

00:09:48.870 --> 00:09:51.540
And this guy now gave an
electron to the carbon.

00:09:51.540 --> 00:09:54.790
So he forms a double bond,
a new double bond.

00:09:54.790 --> 00:09:58.640
So this guy forms a double
bond with the carbon.

00:09:58.640 --> 00:10:04.200
He gave an electron, so he
only has 1, 2, 3, 4, 5, 6

00:10:04.200 --> 00:10:06.420
valence electrons, and
is now neutral.

00:10:06.420 --> 00:10:09.030
Now these can all keep swapping
between each other.

00:10:09.030 --> 00:10:11.160
You can even go from this
structure to that structure.

00:10:11.160 --> 00:10:13.100
You can actually go from any one
of these structures to any

00:10:13.100 --> 00:10:13.990
of the others.

00:10:13.990 --> 00:10:16.990
And the reality of the
carbonate ion, let

00:10:16.990 --> 00:10:18.420
me write this down.

00:10:18.420 --> 00:10:19.670
This is the carbonate ion.

00:10:24.290 --> 00:10:27.710
The reality of it is that its
true structure is some place

00:10:27.710 --> 00:10:29.625
in between all of these.

00:10:32.180 --> 00:10:34.630
So the true structure
of a carbonate ion

00:10:34.630 --> 00:10:35.510
would look like this.

00:10:35.510 --> 00:10:39.330
You would have a carbon and
you'd have three oxygens.

00:10:39.330 --> 00:10:41.750
They have at least one
single bond with each

00:10:41.750 --> 00:10:43.230
of those three oxygens.

00:10:43.230 --> 00:10:47.790
And then you have 1/3 and then
you have-- actually, I should

00:10:47.790 --> 00:10:54.630
say, you have 1/3 of a double
bond with each of them.

00:10:54.630 --> 00:10:56.135
This is a 1/3 of a bond.

00:10:59.480 --> 00:11:03.250
This is not standard notation,
but this is essentially going.

00:11:03.250 --> 00:11:06.100
1/3 of the time, the electron
is on that bond.

00:11:06.100 --> 00:11:08.700
And then the other 2/3 of the
time, each of these oxygens

00:11:08.700 --> 00:11:10.920
have an extra electron.

00:11:10.920 --> 00:11:14.835
You could imagine almost having
a negative 2/3 charge.

00:11:18.160 --> 00:11:20.430
Now, people normally draw one
of these structures because

00:11:20.430 --> 00:11:21.550
this is a nice-- kind of you're

00:11:21.550 --> 00:11:22.530
dealing with whole numbers.

00:11:22.530 --> 00:11:25.900
But the reality of carbonate
ions is that it's experiencing

00:11:25.900 --> 00:11:26.690
this resonance.

00:11:26.690 --> 00:11:29.280
That the electrons are actually
always floating in

00:11:29.280 --> 00:11:31.170
between these forms. Actually
floating across

00:11:31.170 --> 00:11:32.300
all of these bonds.

00:11:32.300 --> 00:11:35.760
And that actually, makes this
molecule more stable.

00:11:35.760 --> 00:11:39.170
This is at a lower energy state
than any of these forms.

00:11:39.170 --> 00:11:41.150
And the same thing is
true with benzene.

00:11:41.150 --> 00:11:43.800
This right here, where we're
in between these two

00:11:43.800 --> 00:11:46.250
structures, is actually at a
lower energy state, a more

00:11:46.250 --> 00:11:49.830
stable state than either
of these forms.