0:00:00.000,0:00:00.600


0:00:00.600,0:00:04.030
If I were to draw a hand, and[br]let me just draw a hand really

0:00:04.030,0:00:07.500
fast, so I'll draw[br]a left hand.

0:00:07.500,0:00:10.620
It looks something like that.

0:00:10.620,0:00:12.220
That is a left hand.

0:00:12.220,0:00:14.970
Now, if I were to take its[br]mirror image, let's say that

0:00:14.970,0:00:18.460
this is a mirror right there,[br]and I want to take its mirror

0:00:18.460,0:00:20.970
image, and I'll draw the[br]mirror image in green.

0:00:20.970,0:00:23.450
So its mirror image would look[br]something like this.

0:00:23.450,0:00:26.540


0:00:26.540,0:00:28.910
Not exact, but you[br]get the idea.

0:00:28.910,0:00:30.590
The mirror image of a left[br]hand looks a lot

0:00:30.590,0:00:32.140
like a right hand.

0:00:32.140,0:00:35.780
Now, no matter how I try to[br]shift or rotate this hand like

0:00:35.780,0:00:39.750
this, I might try to maybe[br]rotate it 180 degrees, so that

0:00:39.750,0:00:42.500
the thumb is on the other side[br]like this image right here.

0:00:42.500,0:00:45.260
But no matter what I do, I will[br]never be able to make

0:00:45.260,0:00:47.340
this thing look like[br]that thing.

0:00:47.340,0:00:50.190
I can shift it and rotate it,[br]it'll just never happen.

0:00:50.190,0:00:53.590
I will never be able to[br]superimpose the blue hand on

0:00:53.590,0:00:54.870
top of this green hand.

0:00:54.870,0:00:58.110
When I say superimpose,[br]literally put it exactly on

0:00:58.110,0:01:00.490
top of the green hand.

0:01:00.490,0:01:04.030
So whenever something is not[br]superimposable on its mirror

0:01:04.030,0:01:25.040
image-- let me write this down--[br]we call it chiral.

0:01:25.040,0:01:27.540
So this hand drawing[br]right here is an

0:01:27.540,0:01:30.380
example of a chiral object.

0:01:30.380,0:01:33.610
Or I guess the hand is an[br]example of a chiral object.

0:01:33.610,0:01:36.750
This is not superimposable[br]on its mirror image.

0:01:36.750,0:01:41.320
And it makes sense that it's[br]called chiral because the word

0:01:41.320,0:01:43.950
chiral comes from the[br]Greek word for hand.

0:01:43.950,0:01:52.170


0:01:52.170,0:01:54.990
And this definition of[br]not being able to be

0:01:54.990,0:01:58.020
superimposable on its mirror[br]image, this applies whether

0:01:58.020,0:02:01.560
you're dealing with chemistry,[br]or mathematics, or I guess,

0:02:01.560,0:02:03.470
just hands in general.

0:02:03.470,0:02:06.150
So if we extend this definition[br]to chemistry,

0:02:06.150,0:02:08.110
because that's what we're[br]talking about, there's two

0:02:08.110,0:02:09.259
concepts here.

0:02:09.259,0:02:17.500
There are chiral molecules,[br]and then there are chiral

0:02:17.500,0:02:21.310
centers or chiral-- well, I call[br]them chiral atoms. They

0:02:21.310,0:02:23.430
tend to be carbon atoms, so[br]sometimes they call them

0:02:23.430,0:02:24.650
chiral carbons.

0:02:24.650,0:02:31.530
So you have these[br]chiral atoms.

0:02:31.530,0:02:34.350
Now, chiral molecules are[br]literally molecules that are

0:02:34.350,0:02:36.370
not superimposable on[br]their mirror image.

0:02:36.370,0:02:39.550


0:02:39.550,0:02:40.720
I'm not going to write[br]the whole thing.

0:02:40.720,0:02:43.120
You know, not superimposable--[br]I'll just

0:02:43.120,0:02:44.480
write the whole thing.

0:02:44.480,0:02:51.310
Not superimposable[br]on mirror image.

0:02:51.310,0:02:55.230


0:02:55.230,0:02:59.300
Now, for chiral atoms, this is[br]essentially true, but when you

0:02:59.300,0:03:04.790
look for chiral atoms within a[br]molecule, the best way to spot

0:03:04.790,0:03:07.760
them is to recognize that these[br]generally, or maybe I

0:03:07.760,0:03:13.620
should say usually, are carbons,[br]especially when we're

0:03:13.620,0:03:16.550
dealing in organic chemistry,[br]but they could be phosphoruses

0:03:16.550,0:03:24.590
or sulfurs, but usually are[br]carbons bonded to four

0:03:24.590,0:03:25.840
different groups.

0:03:25.840,0:03:31.550


0:03:31.550,0:03:34.720
And I want to emphasize[br]groups, not just four

0:03:34.720,0:03:38.250
different atoms. And to kind of[br]highlight a molecule that

0:03:38.250,0:03:41.470
contains a chiral atom or chiral[br]carbon, we can just

0:03:41.470,0:03:42.390
think of one.

0:03:42.390,0:03:45.230
So let's say that I have a[br]carbon right here, and I'm

0:03:45.230,0:03:47.700
going to set this up so this[br]is actually a chiral atom,

0:03:47.700,0:03:51.100
that the carbon specific is a[br]chiral atom, but it's partly a

0:03:51.100,0:03:52.230
chiral molecule.

0:03:52.230,0:03:54.410
And then we'll see examples[br]that one or both

0:03:54.410,0:03:55.670
of these are true.

0:03:55.670,0:04:02.780
Let's say it's bonded[br]to a methyl group.

0:04:02.780,0:04:05.660
From that bond, it kind of[br]pops out of the page.

0:04:05.660,0:04:07.990
Let's say there's a[br]bromine over here.

0:04:07.990,0:04:12.390
Let's say behind it, there is a[br]hydrogen, and then above it,

0:04:12.390,0:04:14.360
we have a fluorine.

0:04:14.360,0:04:16.250
Now if I were to take the mirror[br]image of this thing

0:04:16.250,0:04:20.892
right here, we have your carbon[br]in the center-- I want

0:04:20.892,0:04:22.710
to do it in that same blue.

0:04:22.710,0:04:26.210
You have the carbon in the[br]center and then you have the

0:04:26.210,0:04:28.750
fluorine above the carbon.

0:04:28.750,0:04:31.970
You have your bromine now[br]going in this direction.

0:04:31.970,0:04:33.220
You have this methyl group.

0:04:33.220,0:04:35.800
It's still popping out of the[br]page, but it's now going to

0:04:35.800,0:04:39.800
the right instead of to[br]the left, So CH3.

0:04:39.800,0:04:42.720
And then you have the hydrogen[br]still in the back.

0:04:42.720,0:04:45.320
These are mirror images, if you[br]view this as kind of the

0:04:45.320,0:04:47.970
mirror and you can see on both[br]sides of the mirror.

0:04:47.970,0:04:50.240
Now, why is this chiral?

0:04:50.240,0:04:53.090
Well, it's a little bit of a[br]visualization challenge, but

0:04:53.090,0:04:56.870
no matter how you try to rotate[br]this thing right here,

0:04:56.870,0:04:59.470
you will never make it exactly[br]like this thing.

0:04:59.470,0:05:04.660
You might try to rotate it[br]around like that and try to

0:05:04.660,0:05:08.690
get the methyl group over here,[br]to get it over there.

0:05:08.690,0:05:10.160
So let's try to do that.

0:05:10.160,0:05:13.260
If we try to get the methyl[br]group over there, what's going

0:05:13.260,0:05:15.510
to happen to the other groups?

0:05:15.510,0:05:18.070
Well, then the hydrogen group is[br]going-- or the hydrogen, I

0:05:18.070,0:05:18.340
should say.

0:05:18.340,0:05:20.930
The hydrogen atom is going to[br]move there and the bromine is

0:05:20.930,0:05:23.410
going to move there.

0:05:23.410,0:05:25.440
So this would be superimposable[br]if this was a

0:05:25.440,0:05:28.130
hydrogen and this was a[br]bromine, but it's not.

0:05:28.130,0:05:30.930
You can imagine, the hydrogen[br]and bromine are switched.

0:05:30.930,0:05:33.110
And you could flip it and do[br]whatever else you want or try

0:05:33.110,0:05:35.120
to rotate it in any direction,[br]but you're not going to be

0:05:35.120,0:05:36.650
able to superimpose them.

0:05:36.650,0:05:41.350
So this molecule right here is[br]a chiral molecule, and this

0:05:41.350,0:05:50.710
carbon is a chiral center, so[br]this carbon is a chiral

0:05:50.710,0:05:53.990
carbon, sometimes called[br]an asymmetric

0:05:53.990,0:05:56.970
carbon or a chiral center.

0:05:56.970,0:05:58.360
Sometimes you'll hear[br]something called a

0:05:58.360,0:05:59.265
stereocenter.

0:05:59.265,0:06:02.340
A stereocenter is a more general[br]term for any point in

0:06:02.340,0:06:05.470
a molecule that is asymmetric[br]relative to the different

0:06:05.470,0:06:07.000
groups that it is joined to.

0:06:07.000,0:06:09.350
But all of these, especially[br]when you're in kind of in

0:06:09.350,0:06:13.730
introductory organic chemistry[br]class, tends to be a carbon

0:06:13.730,0:06:16.660
bonded to four different[br]groups.

0:06:16.660,0:06:20.530
And I want to to stress that[br]it's not four different atoms.

0:06:20.530,0:06:23.920
You could have had a methyl[br]group here and a propyl group

0:06:23.920,0:06:27.010
here, and the carbon would still[br]be bonded directly to a

0:06:27.010,0:06:30.740
carbon in either case, but that[br]would still be a chiral

0:06:30.740,0:06:33.790
carbon, and this would still[br]actually be a chiral molecule.

0:06:33.790,0:06:37.150
In the next video, we'll[br]do a bunch of examples.

0:06:37.150,0:06:39.810
We'll look at molecules, try[br]to identify the chiral

0:06:39.810,0:06:41.975
carbons, and then try to[br]figure out whether the

0:06:41.975,0:06:44.180
molecule itself is--

0:06:44.180,0:06:45.533