0:00:00.000,0:00:00.430


0:00:00.430,0:00:03.010
In this video, we're going to[br]look at pairs of molecules and

0:00:03.010,0:00:05.910
see if they relate to each other[br]in any obvious way or

0:00:05.910,0:00:07.820
maybe less than obvious way.

0:00:07.820,0:00:10.840
So these first two right here,[br]they actually look like a

0:00:10.840,0:00:12.260
completely different[br]molecules.

0:00:12.260,0:00:14.110
So your gut impulse might[br]be to say that these are

0:00:14.110,0:00:15.840
completely different[br]molecules.

0:00:15.840,0:00:18.870
And it wouldn't be completely[br]off, but we look a little bit

0:00:18.870,0:00:22.890
closer, you see that this guy[br]on the left has one, two,

0:00:22.890,0:00:26.000
three, four carbons, and so does[br]this guy on the right.

0:00:26.000,0:00:29.010
It has one, two, three,[br]four carbons.

0:00:29.010,0:00:32.400
This guy on the left[br]has two, four, six,

0:00:32.400,0:00:34.400
seven, eight hydrogens.

0:00:34.400,0:00:38.080
This guy on the right has two,[br]four, six, eight hydrogens.

0:00:38.080,0:00:39.680
And they both have one oxygen.

0:00:39.680,0:00:42.030
So both of the molecular[br]formulas for both of these

0:00:42.030,0:00:47.310
things are four carbons, eight[br]hydrogens, and one oxygen.

0:00:47.310,0:00:50.510
They're both C4H8O.

0:00:50.510,0:00:52.200
So they have the same[br]molecular formula.

0:00:52.200,0:00:54.650
They're made up of the same[br]thing, so these are going to

0:00:54.650,0:00:56.380
be isomers.

0:00:56.380,0:00:57.740
They're going to be isomers,[br]and they're a

0:00:57.740,0:00:59.460
special type of isomers.

0:00:59.460,0:01:02.550
In this situation, we don't[br]have the same bonds.

0:01:02.550,0:01:05.570
We're made up of the same[br]things, but the bonds, what is

0:01:05.570,0:01:07.360
connected to what[br]is different.

0:01:07.360,0:01:09.190
So we call this a constitutional[br]isomer.

0:01:09.190,0:01:17.640


0:01:17.640,0:01:21.900
So we are essentially made up of[br]the same things, but we are

0:01:21.900,0:01:25.200
actually two different molecule,[br]actually, two very

0:01:25.200,0:01:26.650
different molecules here.

0:01:26.650,0:01:30.180
Now let's look at this[br]next guy over here.

0:01:30.180,0:01:34.600
So if we look at this molecule,[br]it does look like

0:01:34.600,0:01:36.820
this carbon is chiral.

0:01:36.820,0:01:38.970
It is an asymmetric carbon.

0:01:38.970,0:01:42.820
It is bonded to four different[br]groups: fluorine, bromine,

0:01:42.820,0:01:45.090
hydrogen, and then[br]a methyl group.

0:01:45.090,0:01:46.740
And so's this one.

0:01:46.740,0:01:49.200
And they're both made up[br]of the same things.

0:01:49.200,0:01:51.450
You have the carbon-- and not[br]only are they made up of the

0:01:51.450,0:01:53.440
same things, but the bonding[br]is the same.

0:01:53.440,0:01:56.740
So carbon to a fluorine, carbon[br]to a fluorine, carbon

0:01:56.740,0:01:59.730
to a bromine, carbon to a[br]bromine, carbon to hydrogen in

0:01:59.730,0:02:02.610
both of then carbon to the[br]methyl group in both.

0:02:02.610,0:02:05.020
But they don't look[br]quite the same.

0:02:05.020,0:02:06.260
Are they mirror images?

0:02:06.260,0:02:06.560
Well, no.

0:02:06.560,0:02:09.440
This guy's mirror image would[br]have the fluorine popping out

0:02:09.440,0:02:14.920
here, the hydrogen going back[br]here, and then would have the

0:02:14.920,0:02:16.930
bromine pointing out here.

0:02:16.930,0:02:19.600
Let's see if I can somehow get[br]from this guy to that guy.

0:02:19.600,0:02:24.270
Let me flip this guy first. So[br]let me-- a good thing to do

0:02:24.270,0:02:30.520
would be to just flip to see[br]the fastest way I could

0:02:30.520,0:02:33.340
potentially get there.

0:02:33.340,0:02:35.400
Let me just flip it like this.

0:02:35.400,0:02:37.700
So I'm going to flip out of[br]the page, you can imagine.

0:02:37.700,0:02:39.660
I'm going to flip[br]it like this.

0:02:39.660,0:02:41.870
So I'm going to take this methyl[br]group and then put it

0:02:41.870,0:02:42.810
on the right-hand side.

0:02:42.810,0:02:44.430
And you can imagine, I'm going[br]to turn it so it would come

0:02:44.430,0:02:46.770
out of the page and[br]then go back down.

0:02:46.770,0:02:48.950
So if I did that, what[br]would it look like?

0:02:48.950,0:02:51.130
I would have the carbon,[br]this carbon here.

0:02:51.130,0:02:54.080
I would have the methyl group[br]on that side now.

0:02:54.080,0:02:57.590
And then since I flipped it[br]over, the bromine was in the

0:02:57.590,0:02:58.520
plane of the page.

0:02:58.520,0:03:02.910
It'll still be in the plane of[br]the page, but since I flipped

0:03:02.910,0:03:07.060
it over, the hydrogen, which was[br]in the back, will now be

0:03:07.060,0:03:08.740
in the front.

0:03:08.740,0:03:12.940
The hydrogen will now be in[br]the front and the fluorine

0:03:12.940,0:03:15.620
will now be in back because[br]I flipped it over.

0:03:15.620,0:03:20.320
So the fluorine is[br]now in the back.

0:03:20.320,0:03:22.870
Now, how does this[br]compare to that?

0:03:22.870,0:03:24.570
Let's see if I can somehow[br]get there.

0:03:24.570,0:03:27.610
Well, if I take this fluorine[br]and I rotate it to where the

0:03:27.610,0:03:30.300
hydrogen is, and I take the[br]hydrogen and rotate it to

0:03:30.300,0:03:32.550
where-- that's all going to[br]happen at once-- to where the

0:03:32.550,0:03:34.720
bromine is, and I take the[br]bromine and rotate it to where

0:03:34.720,0:03:36.530
the fluorine is, I get that.

0:03:36.530,0:03:41.860
So I can flip it and then I can[br]rotate it around this bond

0:03:41.860,0:03:44.550
axis right there, and I would[br]get to that molecule there.

0:03:44.550,0:03:46.040
So even though they look pretty[br]different, with the

0:03:46.040,0:03:48.410
flip and a rotation, you[br]actually see that these are

0:03:48.410,0:03:49.660
the same a molecule.

0:03:49.660,0:03:55.340


0:03:55.340,0:03:56.590
Next one.

0:03:56.590,0:03:58.050
So let's see, what[br]do we have here?

0:03:58.050,0:04:00.060
Let me switch colors.

0:04:00.060,0:04:02.820
So over here, this part[br]of both of these

0:04:02.820,0:04:03.960
molecules look the same.

0:04:03.960,0:04:06.380
You have the carbons[br]on both of them.

0:04:06.380,0:04:08.570
This carbon looks like[br]a chiral center.

0:04:08.570,0:04:12.380
It's bonded to one, two,[br]three different groups.

0:04:12.380,0:04:14.470
You might say, oh, it's two[br]carbons, but this is a methyl

0:04:14.470,0:04:16.829
group, and then this side has[br]all this business over it, so

0:04:16.829,0:04:18.700
this is definitely[br]a chiral carbon.

0:04:18.700,0:04:20.829
And over, here same thing.

0:04:20.829,0:04:22.500
It's a chiral carbon.

0:04:22.500,0:04:23.620
And this has the same thing.

0:04:23.620,0:04:25.290
It's bonded to four[br]different things.

0:04:25.290,0:04:28.940
So each of these molecules has[br]two chiral carbons, and it

0:04:28.940,0:04:31.470
looks like they're made[br]up of the same things.

0:04:31.470,0:04:36.250
And not only are they made up[br]of the same things, but the

0:04:36.250,0:04:39.090
bonds are made in[br]the same way.

0:04:39.090,0:04:42.830
So this carbon is bonded to a[br]hydrogen and a fluorine, and

0:04:42.830,0:04:44.760
the two other carbons,[br]same thing, a

0:04:44.760,0:04:46.530
hydrogen and a fluorine.

0:04:46.530,0:04:48.890
Carbon, it looks like[br]it's a hydrogen.

0:04:48.890,0:04:53.310
It's bonded to a hydrogen and a[br]chlorine, so it's made up of

0:04:53.310,0:04:55.350
the same constituents[br]and they're

0:04:55.350,0:04:56.410
bonded in the same way.

0:04:56.410,0:05:00.630
So these look like--[br]but the bonding is

0:05:00.630,0:05:01.820
a little bit different.

0:05:01.820,0:05:04.960
Over here on this one on the[br]left, the hydrogen goes in the

0:05:04.960,0:05:07.510
back, and over here, the[br]hydrogen's in the front.

0:05:07.510,0:05:10.310
And over here, the chlorine's[br]in back, and over here, the

0:05:10.310,0:05:11.560
chlorine's in front.

0:05:11.560,0:05:13.290
So these look like[br]sterioisomers.

0:05:13.290,0:05:18.470


0:05:18.470,0:05:21.630
You saw earlier in this video,[br]you saw structural isomers,

0:05:21.630,0:05:23.290
made up of the same[br]things but the

0:05:23.290,0:05:24.690
connections are all different.

0:05:24.690,0:05:27.920
Stereoisomers, they're made[br]up of the same thing, the

0:05:27.920,0:05:30.380
connections are the same, but[br]the three-dimensional

0:05:30.380,0:05:32.800
configuration is a little[br]bit different.

0:05:32.800,0:05:35.060
For example, here on this[br]carbon, it's connected to the

0:05:35.060,0:05:37.810
same things as this carbon, but[br]over here, the fluorine's

0:05:37.810,0:05:40.750
out front, and over here--[br]out here, the

0:05:40.750,0:05:41.400
fluorine's out front.

0:05:41.400,0:05:43.100
Over here, the fluorine's[br]backwards.

0:05:43.100,0:05:44.540
And same thing for the[br]chlorine here.

0:05:44.540,0:05:46.570
It's back here and[br]it's front here.

0:05:46.570,0:05:52.770
Now, let's see if they're[br]related in a more nuanced way.

0:05:52.770,0:05:55.780
You could imagine putting[br]a mirror behind.

0:05:55.780,0:05:57.470
I guess the best way to[br]visualize it, imagine putting

0:05:57.470,0:06:00.130
a mirror behind this molecule.

0:06:00.130,0:06:02.940
If you put a mirror behind this[br]molecule, what would its

0:06:02.940,0:06:04.570
reflection look like?

0:06:04.570,0:06:06.940
So if you put a mirror behind[br]it, in the image of the

0:06:06.940,0:06:10.470
mirror, this hydrogen would now,[br]since the mirror's behind

0:06:10.470,0:06:12.750
this whole molecule, this[br]hydrogen is actually closer to

0:06:12.750,0:06:13.450
the mirror.

0:06:13.450,0:06:16.307
So then the mirror image, you[br]would have a hydrogen that's

0:06:16.307,0:06:19.530
pointed out, and then you would[br]have the carbon, and

0:06:19.530,0:06:22.770
then you would have the fluorine[br]being further away.

0:06:22.770,0:06:24.930
And same thing in the[br]mirror image here.

0:06:24.930,0:06:27.680
You would have the chlorine[br]coming closer since this

0:06:27.680,0:06:30.270
chlorine is further back, closer[br]to the mirror, and then

0:06:30.270,0:06:33.230
you would have the hydrogen[br]pointing outwards like that.

0:06:33.230,0:06:36.290
And then, obviously, the rest[br]of the molecule would look

0:06:36.290,0:06:38.790
exactly the same.

0:06:38.790,0:06:42.180
And so this mirror image that I[br]just thought about in white

0:06:42.180,0:06:45.710
is exactly what this molecule[br]is: hydrogen pointing out in

0:06:45.710,0:06:49.800
front, hydrogen pointing[br]out in front.

0:06:49.800,0:06:53.110
You might say, wait, this[br]hydrogen is on the right, this

0:06:53.110,0:06:53.710
one's on the left.

0:06:53.710,0:06:54.090
It doesn't matter.

0:06:54.090,0:06:55.690
This is actually saying that[br]the hydrogen's pointing out

0:06:55.690,0:06:58.040
front, the fluorine is pointing[br]out back, hydrogen up

0:06:58.040,0:07:02.010
front, fluorine back, chlorine[br]out front, hydrogen back,

0:07:02.010,0:07:03.930
chlorine out front,[br]hydrogen back.

0:07:03.930,0:07:06.930
So these are actually mirror[br]images, but they're not the

0:07:06.930,0:07:08.900
easy mirror images that we've[br]done in the past where the

0:07:08.900,0:07:12.750
mirror was just like that[br]in between the two.

0:07:12.750,0:07:15.260
This one is a mirror image where[br]you place the mirror

0:07:15.260,0:07:18.300
either on top of or behind[br]one of the molecules.

0:07:18.300,0:07:20.570
So this is a class of[br]stereoisomers, and we've

0:07:20.570,0:07:22.130
brought up this word before.

0:07:22.130,0:07:23.380
We call this enantiomers.

0:07:23.380,0:07:26.000


0:07:26.000,0:07:29.030
So if each of these are an[br]enantiomers, I'll say they are

0:07:29.030,0:07:30.830
enantiomers of each other.

0:07:30.830,0:07:32.390
They're steroisomers.

0:07:32.390,0:07:35.380
They're made up of the same[br]molecules, so that they have

0:07:35.380,0:07:36.680
the same constituents.

0:07:36.680,0:07:40.120
They also have the same[br]connections, and not only do

0:07:40.120,0:07:42.090
they have the same connections,[br]that so far gets

0:07:42.090,0:07:45.100
us a steroisomer, but they are a[br]special kind of stereoisomer

0:07:45.100,0:07:48.450
called an enantiomer, where they[br]are actual mirror images

0:07:48.450,0:07:50.500
of each other.

0:07:50.500,0:07:54.200
Now, what is this one[br]over here in blue?

0:07:54.200,0:07:56.330
Just like the last one, it looks[br]like it's made up of the

0:07:56.330,0:07:57.540
same things.

0:07:57.540,0:08:00.140
You have these carbons, these[br]carbons, these carbons and

0:08:00.140,0:08:01.020
hydrogens up there.

0:08:01.020,0:08:02.590
Same thing over there.

0:08:02.590,0:08:05.120
You have a hydrogen, bromine,[br]hydrogen and a bromine,

0:08:05.120,0:08:08.100
hydrogen, chlorine, hydrogen,[br]chlorine, hydrogen, chlorine,

0:08:08.100,0:08:09.210
hydrogen, chlorine.

0:08:09.210,0:08:10.500
So it's made up of[br]the same things.

0:08:10.500,0:08:14.010
They're connected in the same[br]way, so they're definitely

0:08:14.010,0:08:15.780
stereoisomers.

0:08:15.780,0:08:17.510
Well, we have to make sure[br]they're not-- well, let's make

0:08:17.510,0:08:19.830
sure they're not the same[br]molecule first. Here,

0:08:19.830,0:08:21.520
hydrogen's in the front.

0:08:21.520,0:08:23.770
There, hydrogen's in the back.

0:08:23.770,0:08:25.600
Here, hydrogen is in the back.

0:08:25.600,0:08:26.590
Here, hydrogen is[br]in the front.

0:08:26.590,0:08:28.140
So they're not the[br]same molecule.

0:08:28.140,0:08:30.360
They have a different[br]three-dimensional

0:08:30.360,0:08:33.940
configuration, although their[br]bond connections are the same,

0:08:33.940,0:08:35.190
so these are stereoisomers.

0:08:35.190,0:08:44.430


0:08:44.430,0:08:46.350
Let's see if they're[br]enantiomers.

0:08:46.350,0:08:49.410
So if we look at it like this,[br]you put a mirror here, you

0:08:49.410,0:08:50.720
wouldn't get this[br]guy over here.

0:08:50.720,0:08:52.770
Then you would have a chlorine[br]out front and a hydrogen.

0:08:52.770,0:08:55.140
So you won't get it if you[br]get a mirror over there.

0:08:55.140,0:08:58.450
But if we do the same exercise[br]that we did in the last pair,

0:08:58.450,0:09:02.855
if you put a mirror behind this[br]guy, and I'm just going

0:09:02.855,0:09:05.170
to focus on the stuff that's[br]just forward and back, because

0:09:05.170,0:09:07.160
that's what's relevant[br]if the mirror is

0:09:07.160,0:09:09.250
sitting behind the molecule.

0:09:09.250,0:09:12.570
So if the mirror's sitting[br]behind the molecule, this

0:09:12.570,0:09:15.810
bromine is actually closer to[br]the mirror than that hydrogen.

0:09:15.810,0:09:20.680
So the bromine will now be out[br]front and then the hydrogen

0:09:20.680,0:09:21.380
will be in back.

0:09:21.380,0:09:22.930
This hydrogen will[br]be in the back.

0:09:22.930,0:09:26.120
I'm trying to do kind of a[br]mirror image if it's hard to

0:09:26.120,0:09:27.070
conceptualize.

0:09:27.070,0:09:29.870
And then that would[br]all look the same.

0:09:29.870,0:09:33.890
And then this chlorine will[br]now be out front, and this

0:09:33.890,0:09:37.725
hydrogen will now be in the back[br]in our mirror image, if

0:09:37.725,0:09:39.180
you can visualize it.

0:09:39.180,0:09:40.350
And then we have another one.

0:09:40.350,0:09:43.230
And this chlorine is closer to[br]the mirror that it's kind of

0:09:43.230,0:09:44.940
been sitting on top of.

0:09:44.940,0:09:47.100
So in the mirror image, it would[br]be pointing out, and

0:09:47.100,0:09:49.690
then this hydrogen would[br]be pointing back.

0:09:49.690,0:09:52.550
Now let's see, is our mirror[br]image the same as this?

0:09:52.550,0:09:54.940
So the mirror image, our bromine[br]is pointing in the

0:09:54.940,0:09:57.140
front, hydrogen in[br]the back there.

0:09:57.140,0:10:00.690
Then we have hydrogen in-- then[br]in our mirror image, we

0:10:00.690,0:10:02.270
have the hydrogen in back,[br]chlorine in front.

0:10:02.270,0:10:02.770
Same there.

0:10:02.770,0:10:05.460
So far, it's looking like[br]a mirror image.

0:10:05.460,0:10:08.690
And then in this last carbon[br]over here, chlorine in front,

0:10:08.690,0:10:10.310
hydrogen in back.

0:10:10.310,0:10:12.800
But here, we have chlorine in[br]the back, hydrogen in front.

0:10:12.800,0:10:15.750
So this part, you could[br]think of it this way.

0:10:15.750,0:10:20.360
This is the mirror image of[br]this, this is the mirror image

0:10:20.360,0:10:24.470
of this part, but this is not[br]the mirror image of that part.

0:10:24.470,0:10:27.790
So when you have a stereoisomer[br]that is not a

0:10:27.790,0:10:29.980
mirror, when you have two[br]stereoisomers that aren't

0:10:29.980,0:10:34.330
mirror images of each other,[br]we call them diastereomers.

0:10:34.330,0:10:35.580
I always have trouble[br]saying that.

0:10:35.580,0:10:36.920
Let me write it.

0:10:36.920,0:10:45.990
These are diastereomers, which[br]is essentially saying it's a

0:10:45.990,0:10:48.240
stereoisomer that is[br]not an enantiomer.

0:10:48.240,0:10:50.470
That's all it means: a[br]stereoisomer, not an

0:10:50.470,0:10:51.090
enantiomer.

0:10:51.090,0:10:52.830
A stereoisomer's either going[br]to be an enantiomer or a

0:10:52.830,0:10:54.960
diastereomer.

0:10:54.960,0:10:57.040
Now, let's do this last one.

0:10:57.040,0:11:02.650
Let's see we have two-- we have[br]this cyclohexane ring,

0:11:02.650,0:11:05.950
and they have a bromo on the[br]number one and the number two

0:11:05.950,0:11:07.750
group, depending how[br]you think about it.

0:11:07.750,0:11:11.510
It looks like they are mirror[br]images of each other.

0:11:11.510,0:11:15.050
We could put a mirror right[br]there, and they definitely

0:11:15.050,0:11:16.640
look like mirror images.

0:11:16.640,0:11:18.520
And this is a chiral[br]carbon here.

0:11:18.520,0:11:20.790
It's bonded to one carbon group[br]that is different than

0:11:20.790,0:11:21.550
this carbon group.

0:11:21.550,0:11:23.170
This carbon group[br]has a bromine.

0:11:23.170,0:11:24.080
This carbon group doesn't.

0:11:24.080,0:11:25.750
It just has a bunch of hydrogens[br]on it, if you kind

0:11:25.750,0:11:27.210
of go in that direction.

0:11:27.210,0:11:30.640
And it's hydrogen and then a[br]bromine, so that is chiral.

0:11:30.640,0:11:33.370
And then, same argument,[br]that is also chiral.

0:11:33.370,0:11:36.050
And obviously, this one is[br]chiral and that is chiral.

0:11:36.050,0:11:38.880
But if you think about it, they[br]are mirror images of each

0:11:38.880,0:11:42.370
other, and they each have[br]two chiral centers

0:11:42.370,0:11:44.350
or two chiral carbons.

0:11:44.350,0:11:46.840
But if you think about it, all[br]you have to do is flip this

0:11:46.840,0:11:49.830
guy over and you will[br]get this molecule.

0:11:49.830,0:11:51.970
These are the same molecules.

0:11:51.970,0:11:56.380
So it is the same molecule.

0:11:56.380,0:11:59.050
So this is interesting, and we[br]saw this when we first learned

0:11:59.050,0:12:00.220
about chirality.

0:12:00.220,0:12:03.350
Even though we have two chiral[br]centers, this is

0:12:03.350,0:12:04.650
not a chiral molecule.

0:12:04.650,0:12:06.690
It is the same thing as[br]its mirror image.

0:12:06.690,0:12:10.180
It is superimposable on[br]its mirror image.

0:12:10.180,0:12:23.410
It is superimposable on[br]its mirror image.

0:12:23.410,0:12:27.540
So even though it has chiral[br]carbons in it, it is not a

0:12:27.540,0:12:29.380
chiral molecule.

0:12:29.380,0:12:31.530
And we call these[br]meso compounds.

0:12:31.530,0:12:34.700


0:12:34.700,0:12:36.510
And we can point to one of them[br]because they really are

0:12:36.510,0:12:37.660
the same compound.

0:12:37.660,0:12:41.590
This is a meso compound.

0:12:41.590,0:12:43.770
It has chiral centers.

0:12:43.770,0:12:45.960
It has chiral carbons, I[br]guess you could say it.

0:12:45.960,0:12:48.360
But it is not a chiral[br]compound.

0:12:48.360,0:12:50.350
And the way to spot these fairly[br]straightforward is that

0:12:50.350,0:12:52.500
you have chiral centers,[br]but there is a

0:12:52.500,0:12:54.170
line of symmetry here.

0:12:54.170,0:12:56.110
There's a line of symmetry[br]right here.

0:12:56.110,0:12:59.690
These two sides of the compound[br]are mirror images of

0:12:59.690,0:13:00.430
each other.

0:13:00.430,0:13:05.190
Now, these would not be the same[br]molecule if I change that

0:13:05.190,0:13:09.310
to a fluorine and I change[br]that to a fluorine.

0:13:09.310,0:13:11.780
Then all of a sudden, you do[br]not have this symmetry.

0:13:11.780,0:13:14.180
These are mirror images,[br]but they would not be

0:13:14.180,0:13:15.060
superimposable.

0:13:15.060,0:13:17.650
So if that was a fluorine,[br]these would actually be

0:13:17.650,0:13:18.790
enantiomers.

0:13:18.790,0:13:22.110
And this would not be only one[br]meso compound, it would be two

0:13:22.110,0:13:27.860
different enantiomers, and one[br]of them would have an R

0:13:27.860,0:13:30.340
direction and one of them would[br]have an S direction if

0:13:30.340,0:13:33.040
we go with the naming[br]conventions that we learned.

0:13:33.040,0:13:35.466