0:00:00.000,0:00:00.660


0:00:00.660,0:00:02.340
Fischer projections[br]are another way

0:00:02.340,0:00:04.660
of visualizing molecules[br]in three dimensions.

0:00:04.660,0:00:07.570
And let's use the[br]example of lactic acid.

0:00:07.570,0:00:09.070
It's called lactic[br]acid since it has

0:00:09.070,0:00:12.200
a carboxylic acid functional[br]group over here on the right.

0:00:12.200,0:00:15.260
And this is the only chirality[br]center in lactic acid.

0:00:15.260,0:00:17.530
It's an sp3 hybridized[br]carbon with four

0:00:17.530,0:00:19.400
different substituents[br]attached to it.

0:00:19.400,0:00:20.890
So with only one[br]chirality center,

0:00:20.890,0:00:23.690
we would expect to[br]have two stereoisomers

0:00:23.690,0:00:25.050
for this molecule.

0:00:25.050,0:00:27.940
And those stereoisomers would[br]be enantiomers of each other.

0:00:27.940,0:00:30.470
Over here, I've picked[br]one of those enantiomers.

0:00:30.470,0:00:32.420
And I've just drawn[br]it in this fashion.

0:00:32.420,0:00:34.630
Let's see which enantiomer[br]we have over here.

0:00:34.630,0:00:36.780
Well, this is my[br]chirality center,

0:00:36.780,0:00:38.440
the one attached to my OH.

0:00:38.440,0:00:40.720
And if I were to assign[br]absolute configuration

0:00:40.720,0:00:43.400
to that chirality center,[br]I look at the first atom

0:00:43.400,0:00:45.065
connected to that[br]chirality center.

0:00:45.065,0:00:47.590
Well, that's oxygen[br]versus carbon

0:00:47.590,0:00:49.550
versus a carbon over[br]here in my carbonyl.

0:00:49.550,0:00:52.120
So obviously,[br]oxygen's going to win.

0:00:52.120,0:00:55.390
So we can assign oxygen[br]a number 1 priority

0:00:55.390,0:00:57.390
since it has the[br]highest atomic number.

0:00:57.390,0:01:01.180
And when I compare these[br]two carbons to each other,

0:01:01.180,0:01:04.560
I know the carbon on the right[br]is double bonded to an oxygen.

0:01:04.560,0:01:07.210
So that's going to give it[br]higher priority than the carbon

0:01:07.210,0:01:09.820
over here on the left since[br]that's bonded to hydrogens.

0:01:09.820,0:01:12.970
And then my other hydrogen[br]attached to my chirality center

0:01:12.970,0:01:15.000
is going away from me in space.

0:01:15.000,0:01:17.380
So when I'm assigning[br]absolute configuration,

0:01:17.380,0:01:19.930
I look at the fact that[br]it's going one, two, three.

0:01:19.930,0:01:21.080
It's going around this way.

0:01:21.080,0:01:22.470
It's going around clockwise.

0:01:22.470,0:01:25.620
Therefore, this is the R[br]enantiomer of lactic acid.

0:01:25.620,0:01:27.500
So that's all from[br]a previous video.

0:01:27.500,0:01:30.940
Now, if I want to draw a Fischer[br]projection of R lactic acid,

0:01:30.940,0:01:34.070
what I would do is I would[br]put my eye right here.

0:01:34.070,0:01:36.775
And I would stare down[br]at my chirality center.

0:01:36.775,0:01:39.990


0:01:39.990,0:01:42.740
And I would draw[br]exactly what I see.

0:01:42.740,0:01:44.880
Well, if I'm staring[br]down this way,

0:01:44.880,0:01:47.250
I could draw a line[br]right here to represent

0:01:47.250,0:01:49.390
my flat sheet of paper.

0:01:49.390,0:01:52.760
And I can see that both[br]my hydrogen and my OH

0:01:52.760,0:01:56.200
are above my sheet of paper,[br]whereas my carboxylic acid

0:01:56.200,0:01:59.140
and my CH3 are below[br]my sheet of paper.

0:01:59.140,0:02:02.940
So this carbon is my[br]chirality center carbon.

0:02:02.940,0:02:07.460
And I have my OH[br]coming out at me.

0:02:07.460,0:02:10.220
And this is actually going[br]to be on the right side.

0:02:10.220,0:02:12.552
So if you take out your[br]molecular model set,

0:02:12.552,0:02:14.510
you will see this OH will[br]be coming out at you.

0:02:14.510,0:02:16.660
And it will be on the[br]right side of you.

0:02:16.660,0:02:18.562
And this hydrogen will[br]be coming out at you,

0:02:18.562,0:02:20.187
and it will be on[br]the left side of you.

0:02:20.187,0:02:22.800
So that hydrogen would[br]go over here like that.

0:02:22.800,0:02:25.940
This carboxylic acid[br]functional group-- this

0:02:25.940,0:02:27.580
is the top my head right here.

0:02:27.580,0:02:30.610
Then that would make this go at[br]the top of what I'm looking at.

0:02:30.610,0:02:33.190
And so that is going[br]away from me in space.

0:02:33.190,0:02:35.480
So we would use a dash[br]to represent that.

0:02:35.480,0:02:39.530
And so we could go ahead and[br]draw our C double bond to an O.

0:02:39.530,0:02:41.700
And then an OH[br]going away from me.

0:02:41.700,0:02:44.328
And then if I look at[br]this CH3 group over here,

0:02:44.328,0:02:45.536
it's also going away from me.

0:02:45.536,0:02:46.770
It's going down in space.

0:02:46.770,0:02:51.220
So I can represent it going[br]down in space like that.

0:02:51.220,0:02:54.160
And this is the viewpoint[br]of a Fischer projection.

0:02:54.160,0:02:56.890
So if I'm going to convert[br]this into a Fischer projection,

0:02:56.890,0:03:00.680
a Fischer projection is just[br]drawing a cross like that.

0:03:00.680,0:03:03.060
And then at the top, you[br]have your C double bonded

0:03:03.060,0:03:05.070
to an O and then[br]an OH as just a way

0:03:05.070,0:03:08.420
of abbreviating this carboxylic[br]acid functional group.

0:03:08.420,0:03:10.240
And then I have a[br]hydrogen over here.

0:03:10.240,0:03:12.510
And then I have an[br]OH group over here.

0:03:12.510,0:03:13.990
And then I have a CH3 here.

0:03:13.990,0:03:16.280
So this is a Fischer projection.

0:03:16.280,0:03:19.290
This is the Fischer[br]projection for R lactic acid.

0:03:19.290,0:03:21.130
So this is R lactic acid.

0:03:21.130,0:03:24.040
And Fischer projections[br]were invented

0:03:24.040,0:03:27.967
by Emil Fischer, who won the[br]Nobel Prize in chemistry.

0:03:27.967,0:03:30.300
One of the things was for his[br]research in carbohydrates.

0:03:30.300,0:03:33.579
And he drew Fischer projections[br]to help him draw carbohydrates.

0:03:33.579,0:03:35.870
And so that's where you'll[br]see Fischer projections used

0:03:35.870,0:03:37.953
most often, even though[br]some chemists don't really

0:03:37.953,0:03:38.870
like them very much.

0:03:38.870,0:03:41.570
So this is the Fischer[br]projection for R lactic acid.

0:03:41.570,0:03:44.480
And if I wanted to draw the[br]Fischer projection for S

0:03:44.480,0:03:47.360
lactic acid, I[br]would just reflect

0:03:47.360,0:03:49.500
this molecule in a mirror.

0:03:49.500,0:03:52.840
So let's see if I can fit[br]my mirror in over here.

0:03:52.840,0:03:57.250
And I would have my OH[br]reflected in my mirror.

0:03:57.250,0:04:00.660
And then I'd go ahead and[br]draw my Fischer projection.

0:04:00.660,0:04:03.170
And then my methyl group[br]would be over here.

0:04:03.170,0:04:04.950
My hydrogen would be over here.

0:04:04.950,0:04:07.760
And my carboxylic[br]acid functional group

0:04:07.760,0:04:08.720
would be right there.

0:04:08.720,0:04:11.190
So this would be S lactic[br]acid on the right and R

0:04:11.190,0:04:13.490
lactic acid on the left.

0:04:13.490,0:04:16.579
S lactic acid is the[br]type of lactic acid

0:04:16.579,0:04:20.649
you find in the buildup of[br]muscles after extreme exercise.

0:04:20.649,0:04:22.880
And the type of lactic[br]acid that some people have

0:04:22.880,0:04:26.800
heard of from milk is[br]actually a racemic mixture.

0:04:26.800,0:04:30.780
So the bacteria in sour milk[br]will break down the lactose

0:04:30.780,0:04:36.010
into a 50% mixture of R and a[br]50% mixture of S lactic acid.

0:04:36.010,0:04:38.210
Let's take a look[br]at a carbohydrate,

0:04:38.210,0:04:42.100
since Fischer used Fischer[br]projections for carbohydrates,

0:04:42.100,0:04:42.730
specifically.

0:04:42.730,0:04:45.190
So here I have a carbohydrate.

0:04:45.190,0:04:48.280
And if I were to number[br]this carbohydrate,

0:04:48.280,0:04:51.630
this carbonyl would[br]get a number 1.

0:04:51.630,0:04:54.180
And then this would get[br]a number 2 over here,

0:04:54.180,0:04:56.360
a number 4, and a number 4.

0:04:56.360,0:04:58.540
This is a four-carbon[br]carbohydrate.

0:04:58.540,0:05:01.830
How many stereoisomers does[br]this carbohydrate have?

0:05:01.830,0:05:06.110
Well, this carbon number[br]2 is a chirality center.

0:05:06.110,0:05:09.700
And carbon number 3[br]is a chirality center,

0:05:09.700,0:05:11.690
so 2 chirality centers.

0:05:11.690,0:05:14.360
So I use the formula[br]of 2 to the n,

0:05:14.360,0:05:16.390
where n is the number[br]of chirality centers.

0:05:16.390,0:05:21.250
So I would expect 2 squared,[br]or 4 possible stereoisomers

0:05:21.250,0:05:22.140
for this molecule.

0:05:22.140,0:05:24.120
So you could draw four[br]different stereoisomers

0:05:24.120,0:05:24.960
for this molecule.

0:05:24.960,0:05:26.600
We'll draw them[br]in a few minutes.

0:05:26.600,0:05:30.660
For right now, I've gone[br]ahead and drawn one of them

0:05:30.660,0:05:32.510
as a sawhorse projection.

0:05:32.510,0:05:35.490
So here I have a sawhorse[br]projection of one

0:05:35.490,0:05:38.340
of the possible stereoisomers.

0:05:38.340,0:05:40.220
And what we're[br]going to do is we're

0:05:40.220,0:05:43.320
going to put our[br]eye right up here.

0:05:43.320,0:05:47.940
And we're going to stare[br]straight down at this bond

0:05:47.940,0:05:48.670
right here.

0:05:48.670,0:05:50.790
And we're going to see if[br]we can draw the Fischer

0:05:50.790,0:05:52.350
projection for this molecule.

0:05:52.350,0:05:54.500
So what do we see?

0:05:54.500,0:05:58.620
Well, let's start with[br]this carbon right up here.

0:05:58.620,0:06:00.790
So we'll make that[br]carbon this one.

0:06:00.790,0:06:06.830
And you can see that the[br]OH attached to that carbon

0:06:06.830,0:06:07.920
is going to the right.

0:06:07.920,0:06:10.000
And it's going up at us.

0:06:10.000,0:06:14.080
So that OH is going to the[br]right, and it's going up at us.

0:06:14.080,0:06:17.250
And then if I look at[br]this hydrogen over here,

0:06:17.250,0:06:17.960
it's on the left.

0:06:17.960,0:06:19.590
And it's going up at us.

0:06:19.590,0:06:24.100
So my hydrogen is on the[br]left and it's going up at us.

0:06:24.100,0:06:29.500
And this aldehyde functional[br]group, this CHO, you can see

0:06:29.500,0:06:32.110
is going down.

0:06:32.110,0:06:35.110
So this aldehyde functional[br]group is going away from us.

0:06:35.110,0:06:37.170
So we can go ahead and[br]represent that aldehyde

0:06:37.170,0:06:40.820
as going away from us[br]in space like that.

0:06:40.820,0:06:44.080
Well, this chirality[br]center carbon

0:06:44.080,0:06:47.280
is connected to this[br]chirality center carbon.

0:06:47.280,0:06:49.100
So we'll go ahead and[br]draw a straight line,

0:06:49.100,0:06:50.870
since we're looking[br]straight down at it.

0:06:50.870,0:06:53.610
And once again, we will[br]find that our OH group

0:06:53.610,0:06:55.540
is on the right[br]coming out at us.

0:06:55.540,0:06:58.740
Our hydrogen is on the[br]left coming out at us.

0:06:58.740,0:07:00.700
So let's go ahead[br]and put those in.

0:07:00.700,0:07:02.890
OH group is on the[br]right coming out at us.

0:07:02.890,0:07:05.230
Hydrogen is on the[br]left coming out at us.

0:07:05.230,0:07:09.040
And then, of course, we[br]have this CH2OH down here

0:07:09.040,0:07:10.620
as going away from us in space.

0:07:10.620,0:07:14.670
So we'll go ahead and[br]draw that CH2OH going away

0:07:14.670,0:07:15.860
from us in space like that.

0:07:15.860,0:07:20.110
So that would be the Fischer[br]projection translated.

0:07:20.110,0:07:22.690
Let's go ahead and make it into[br]an actual Fischer projection

0:07:22.690,0:07:25.730
where we just go ahead[br]and draw straight lines.

0:07:25.730,0:07:27.790
And the intersection[br]of those straight lines

0:07:27.790,0:07:31.660
are where our[br]chirality centers are.

0:07:31.660,0:07:35.310
So this would be an H.[br]This would be an OH.

0:07:35.310,0:07:36.140
This would be an H.

0:07:36.140,0:07:37.250
This would be an OH.

0:07:37.250,0:07:39.050
This would be our CH2OH.

0:07:39.050,0:07:42.350
And then at the top, we[br]have our aldehyde, CHO.

0:07:42.350,0:07:45.890
So this is one of the four[br]possible stereoisomers.

0:07:45.890,0:07:47.890
And Fischer projections[br]just make it much easier

0:07:47.890,0:07:49.350
when we're working[br]with carbohydrates.

0:07:49.350,0:07:50.490
So this is one of the four.

0:07:50.490,0:07:52.450
Let's go ahead and redraw[br]the one we just drew

0:07:52.450,0:07:55.702
and let's get the other three to[br]get our total of four on here.

0:07:55.702,0:07:58.160
So I'm going to take the one[br]that I just drew on the right.

0:07:58.160,0:07:59.460
I'm going to redraw it.

0:07:59.460,0:08:01.220
I'm going to draw it a little[br]bit smaller so everything

0:08:01.220,0:08:02.055
will fit in here.

0:08:02.055,0:08:06.030
So this is one[br]possible stereoisomer.

0:08:06.030,0:08:08.910
I have my OHs on the right.

0:08:08.910,0:08:10.900
I have my hydrogens.

0:08:10.900,0:08:12.760
I have my CHO.

0:08:12.760,0:08:13.456
I have my CH2OH.

0:08:13.456,0:08:16.450


0:08:16.450,0:08:19.560
If I wanted to draw the[br]enantiomer to this molecule,

0:08:19.560,0:08:22.760
I would just have to[br]reflect it in a mirror.

0:08:22.760,0:08:24.150
So I could just do this.

0:08:24.150,0:08:27.190
I could reflect the[br]molecule in a mirror,

0:08:27.190,0:08:29.730
and I would have the enantiomer.

0:08:29.730,0:08:33.429
So this would be the[br]enantiomer to the stereoisomer

0:08:33.429,0:08:35.470
that I just drew.

0:08:35.470,0:08:38.289
If I wanted to[br]draw the other two,

0:08:38.289,0:08:39.789
I can just go ahead[br]and real quickly

0:08:39.789,0:08:42.179
put in my Fischer[br]projections right here.

0:08:42.179,0:08:44.610
So I have two more to go.

0:08:44.610,0:08:50.840
And I'm going to put the OH over[br]here, and then the H over here,

0:08:50.840,0:08:54.650
and then the OH over[br]here, and the H over here.

0:08:54.650,0:08:58.530
So this is yet another[br]possible stereoisomer.

0:08:58.530,0:09:01.530
And I'll draw the mirror[br]image over here on the right.

0:09:01.530,0:09:04.230
So I have to have a[br]hydrogen right here.

0:09:04.230,0:09:06.850
And then my OH must[br]be on this side.

0:09:06.850,0:09:11.420
And then I must have an[br]OH right here, and then

0:09:11.420,0:09:14.975
a hydrogen on the other side,[br]and then a CHO for my aldehyde,

0:09:14.975,0:09:17.200
and a CH2OH.

0:09:17.200,0:09:20.420
So here I have my four[br]possible stereoisomers

0:09:20.420,0:09:22.792
for this carbohydrate.

0:09:22.792,0:09:24.500
And I'm going to go[br]ahead and label them.

0:09:24.500,0:09:27.170
I'm going to label this[br]first one here stereoisomer

0:09:27.170,0:09:31.760
A, stereoisomer B, stereoisomer[br]C, and stereoisomer D.

0:09:31.760,0:09:34.860
Well, C and D are mirror[br]images of each other.

0:09:34.860,0:09:37.169
So they are enantiomers[br]of each other.

0:09:37.169,0:09:38.210
So these are enantiomers.

0:09:38.210,0:09:40.820
A and B are mirror[br]images, so they

0:09:40.820,0:09:42.790
are enantiomers to each other.

0:09:42.790,0:09:45.600
And then we talked about[br]in the diastereomer video,

0:09:45.600,0:09:51.170
if I took one of the ones from A[br]and B-- so let me just go ahead

0:09:51.170,0:09:53.030
and circle that--[br]if I just took A.

0:09:53.030,0:09:55.780
If I took one of the ones from[br]A and B and one of the ones

0:09:55.780,0:09:58.000
from C and D, and[br]I'll just take C. Then

0:09:58.000,0:10:00.930
A and C are diastereomers[br]of each other.

0:10:00.930,0:10:04.910
They are non-superimposable,[br]non-mirror images

0:10:04.910,0:10:05.570
of each other.

0:10:05.570,0:10:07.750
So those are enantiomers[br]and diastereomers,

0:10:07.750,0:10:11.349
to review what we covered[br]in an earlier video.

0:10:11.349,0:10:13.390
Let's do one more thing[br]with Fischer projections.

0:10:13.390,0:10:16.270
Let's assign absolute[br]configurations

0:10:16.270,0:10:18.860
to one of the stereoisomers.

0:10:18.860,0:10:20.780
So let's just choose[br]the first one, A.

0:10:20.780,0:10:23.030
So we've been talking[br]about A. And let's go ahead

0:10:23.030,0:10:24.930
and redraw it really fast.

0:10:24.930,0:10:29.410
And let's see how can we figure[br]out the absolute configuration

0:10:29.410,0:10:34.357
at my chirality centers[br]from a Fischer projection.

0:10:34.357,0:10:36.440
So it just makes a little[br]bit trickier than usual.

0:10:36.440,0:10:38.330
So here I have my[br]Fischer projection.

0:10:38.330,0:10:40.250
And your aldehyde's[br]going to get a 1,

0:10:40.250,0:10:44.232
and then 2, 3, 4 in terms of[br]numbering your carbon chain.

0:10:44.232,0:10:46.190
I want to figure out the[br]absolute configuration

0:10:46.190,0:10:47.650
at carbon 2 here.

0:10:47.650,0:10:49.930
So at carbon 2, what do I have?

0:10:49.930,0:10:52.060
I know a Fischer[br]projection tells me

0:10:52.060,0:10:55.760
that if it's a horizontal line,[br]everything is coming out at me.

0:10:55.760,0:10:57.430
So my OH is coming out at me.

0:10:57.430,0:10:59.950
And my hydrogen is[br]coming out at me.

0:10:59.950,0:11:03.620
Let's go back up here and stare[br]down that carbon 2 chirality

0:11:03.620,0:11:04.120
center.

0:11:04.120,0:11:06.760
And let's see what we would[br]actually see if we do that.

0:11:06.760,0:11:09.390
So here is carbon 2 right here.

0:11:09.390,0:11:12.640
I'm going to stare down[br]right here this time.

0:11:12.640,0:11:15.070
So I have my OH[br]coming out at me,

0:11:15.070,0:11:17.240
my hydrogen coming out at me.

0:11:17.240,0:11:19.280
That makes this[br]bond and this bond

0:11:19.280,0:11:22.030
to actually go away[br]from me in space.

0:11:22.030,0:11:24.050
So the aldehyde is[br]going to go away

0:11:24.050,0:11:27.010
from me in space like that.

0:11:27.010,0:11:29.629
So I'm going to go ahead[br]and draw my aldehyde.

0:11:29.629,0:11:31.920
Now, I'm actually going to[br]go ahead and show the carbon

0:11:31.920,0:11:33.140
bond to one hydrogen.

0:11:33.140,0:11:35.519
I know the carbon's double[br]bonded to an oxygen,

0:11:35.519,0:11:36.810
so I'm going to go and do that.

0:11:36.810,0:11:38.893
That was that trick we[br]learned in an earlier video

0:11:38.893,0:11:40.490
for assigning absolute[br]configuration.

0:11:40.490,0:11:41.948
And then the rest[br]of the molecule's

0:11:41.948,0:11:43.370
actually going down in space.

0:11:43.370,0:11:46.290
So this would be a carbon[br]here bonded to a hydrogen.

0:11:46.290,0:11:48.950
And this carbon is bonded[br]to an oxygen and a carbon.

0:11:48.950,0:11:50.690
So what is the[br]absolute configuration

0:11:50.690,0:11:51.720
of this carbon here?

0:11:51.720,0:11:56.990
Well, if I think about this[br]is my chirality center,

0:11:56.990,0:11:59.210
what are the atoms directly[br]attached to that carbon?

0:11:59.210,0:12:01.690
Well, I have a hydrogen,[br]a carbon, an oxygen,

0:12:01.690,0:12:02.320
and a carbon.

0:12:02.320,0:12:06.670
Well, immediately I know that[br]my oxygen is going to win.

0:12:06.670,0:12:09.980
So I can go ahead and assign[br]a number 1 to my oxygen right

0:12:09.980,0:12:10.650
here.

0:12:10.650,0:12:13.070
And then I think about[br]what's next priority.

0:12:13.070,0:12:15.800
Well, it would be[br]carbon versus carbon.

0:12:15.800,0:12:19.450
So at the top, I have[br]oxygen, oxygen, hydrogen.

0:12:19.450,0:12:22.410
The bottom carbon, I have[br]oxygen, carbon, hydrogen.

0:12:22.410,0:12:24.080
So we saw in an[br]earlier video, you

0:12:24.080,0:12:25.455
go for first point[br]of difference.

0:12:25.455,0:12:27.750
So oxygen versus[br]oxygen, no one wins.

0:12:27.750,0:12:30.280
Then I go oxygen versus[br]carbon, and oxygen wins.

0:12:30.280,0:12:32.160
So this would get[br]a number 2 up here.

0:12:32.160,0:12:34.430
And then this would get a[br]number 3 for my substituent.

0:12:34.430,0:12:36.380
And my hydrogen[br]would get a number 4.

0:12:36.380,0:12:38.340
So I'm going around this way.

0:12:38.340,0:12:42.500
I am going around this way,[br]if I ignore my hydrogen.

0:12:42.500,0:12:44.460
So I'm going counterclockwise.

0:12:44.460,0:12:48.400
So it looks like it's S.[br]But remember, the hydrogen

0:12:48.400,0:12:50.070
is actually coming out at me.

0:12:50.070,0:12:53.229
So in the little trick I showed[br]you in the earlier video,

0:12:53.229,0:12:55.520
if the hydrogen is coming[br]out at me, all you have to do

0:12:55.520,0:12:56.560
is reverse it.

0:12:56.560,0:13:00.000
So it looks like it's S, but[br]since the hydrogen's coming out

0:13:00.000,0:13:02.710
at, me, I can go ahead[br]and say with certainty

0:13:02.710,0:13:05.560
that it is R at that[br]chirality center.

0:13:05.560,0:13:09.730
So at carbon 2, at[br]this carbon, it is R.

0:13:09.730,0:13:13.190
So you can do the same thing[br]with the chirality center

0:13:13.190,0:13:14.540
at the third position.

0:13:14.540,0:13:17.130
So you could do the same[br]thing with this one.

0:13:17.130,0:13:20.380
And if you do that, you[br]will find that it is also R.

0:13:20.380,0:13:23.090
So you could go ahead and[br]say for this carbohydrate,

0:13:23.090,0:13:27.730
it is R at carbon 2,[br]and it is R at carbon 3.

0:13:27.730,0:13:29.840
So it is 2R, 3R.

0:13:29.840,0:13:32.140
And there's a 2R,[br]3R stereoisomer.

0:13:32.140,0:13:35.930
And you could do that for[br]all four of the stereoisomers

0:13:35.930,0:13:37.750
that we drew for[br]this carbohydrate.

0:13:37.750,0:13:40.580
And you could then compare[br]enantiomers and diastereomers

0:13:40.580,0:13:41.670
that way, as well.

0:13:41.670,0:13:44.570
So that's a quick summary[br]of Fischer projections.

0:13:44.570,0:13:45.200
Practice.

0:13:45.200,0:13:47.930
And use your molecular[br]model set to help you

0:13:47.930,0:13:50.530
with the visualization aspect.

0:13:50.530,0:13:51.296