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00:00:00,000 --> 00:00:00,660


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00:00:00,660 --> 00:00:02,340
Fischer projections
are another way

3
00:00:02,340 --> 00:00:04,660
of visualizing molecules
in three dimensions.

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00:00:04,660 --> 00:00:07,570
And let's use the
example of lactic acid.

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00:00:07,570 --> 00:00:09,070
It's called lactic
acid since it has

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00:00:09,070 --> 00:00:12,200
a carboxylic acid functional
group over here on the right.

7
00:00:12,200 --> 00:00:15,260
And this is the only chirality
center in lactic acid.

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00:00:15,260 --> 00:00:17,530
It's an sp3 hybridized
carbon with four

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00:00:17,530 --> 00:00:19,400
different substituents
attached to it.

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00:00:19,400 --> 00:00:20,890
So with only one
chirality center,

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00:00:20,890 --> 00:00:23,690
we would expect to
have two stereoisomers

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00:00:23,690 --> 00:00:25,050
for this molecule.

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And those stereoisomers would
be enantiomers of each other.

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Over here, I've picked
one of those enantiomers.

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And I've just drawn
it in this fashion.

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Let's see which enantiomer
we have over here.

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00:00:34,630 --> 00:00:36,780
Well, this is my
chirality center,

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the one attached to my OH.

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And if I were to assign
absolute configuration

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to that chirality center,
I look at the first atom

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connected to that
chirality center.

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Well, that's oxygen
versus carbon

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00:00:47,590 --> 00:00:49,550
versus a carbon over
here in my carbonyl.

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So obviously,
oxygen's going to win.

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So we can assign oxygen
a number 1 priority

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00:00:55,390 --> 00:00:57,390
since it has the
highest atomic number.

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00:00:57,390 --> 00:01:01,180
And when I compare these
two carbons to each other,

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I know the carbon on the right
is double bonded to an oxygen.

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So that's going to give it
higher priority than the carbon

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over here on the left since
that's bonded to hydrogens.

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And then my other hydrogen
attached to my chirality center

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is going away from me in space.

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So when I'm assigning
absolute configuration,

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I look at the fact that
it's going one, two, three.

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It's going around this way.

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It's going around clockwise.

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Therefore, this is the R
enantiomer of lactic acid.

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So that's all from
a previous video.

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00:01:27,500 --> 00:01:30,940
Now, if I want to draw a Fischer
projection of R lactic acid,

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what I would do is I would
put my eye right here.

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And I would stare down
at my chirality center.

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00:01:36,775 --> 00:01:39,990


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And I would draw
exactly what I see.

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Well, if I'm staring
down this way,

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I could draw a line
right here to represent

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my flat sheet of paper.

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And I can see that both
my hydrogen and my OH

48
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are above my sheet of paper,
whereas my carboxylic acid

49
00:01:56,200 --> 00:01:59,140
and my CH3 are below
my sheet of paper.

50
00:01:59,140 --> 00:02:02,940
So this carbon is my
chirality center carbon.

51
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And I have my OH
coming out at me.

52
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And this is actually going
to be on the right side.

53
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So if you take out your
molecular model set,

54
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you will see this OH will
be coming out at you.

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And it will be on the
right side of you.

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And this hydrogen will
be coming out at you,

57
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and it will be on
the left side of you.

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So that hydrogen would
go over here like that.

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This carboxylic acid
functional group-- this

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is the top my head right here.

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Then that would make this go at
the top of what I'm looking at.

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And so that is going
away from me in space.

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So we would use a dash
to represent that.

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And so we could go ahead and
draw our C double bond to an O.

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And then an OH
going away from me.

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And then if I look at
this CH3 group over here,

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it's also going away from me.

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It's going down in space.

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So I can represent it going
down in space like that.

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And this is the viewpoint
of a Fischer projection.

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00:02:54,160 --> 00:02:56,890
So if I'm going to convert
this into a Fischer projection,

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a Fischer projection is just
drawing a cross like that.

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And then at the top, you
have your C double bonded

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to an O and then
an OH as just a way

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of abbreviating this carboxylic
acid functional group.

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And then I have a
hydrogen over here.

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And then I have an
OH group over here.

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And then I have a CH3 here.

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So this is a Fischer projection.

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00:03:16,280 --> 00:03:19,290
This is the Fischer
projection for R lactic acid.

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So this is R lactic acid.

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And Fischer projections
were invented

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by Emil Fischer, who won the
Nobel Prize in chemistry.

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One of the things was for his
research in carbohydrates.

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And he drew Fischer projections
to help him draw carbohydrates.

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And so that's where you'll
see Fischer projections used

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most often, even though
some chemists don't really

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like them very much.

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So this is the Fischer
projection for R lactic acid.

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And if I wanted to draw the
Fischer projection for S

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lactic acid, I
would just reflect

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this molecule in a mirror.

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So let's see if I can fit
my mirror in over here.

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And I would have my OH
reflected in my mirror.

95
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And then I'd go ahead and
draw my Fischer projection.

96
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And then my methyl group
would be over here.

97
00:04:03,170 --> 00:04:04,950
My hydrogen would be over here.

98
00:04:04,950 --> 00:04:07,760
And my carboxylic
acid functional group

99
00:04:07,760 --> 00:04:08,720
would be right there.

100
00:04:08,720 --> 00:04:11,190
So this would be S lactic
acid on the right and R

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00:04:11,190 --> 00:04:13,490
lactic acid on the left.

102
00:04:13,490 --> 00:04:16,579
S lactic acid is the
type of lactic acid

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00:04:16,579 --> 00:04:20,649
you find in the buildup of
muscles after extreme exercise.

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00:04:20,649 --> 00:04:22,880
And the type of lactic
acid that some people have

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heard of from milk is
actually a racemic mixture.

106
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So the bacteria in sour milk
will break down the lactose

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into a 50% mixture of R and a
50% mixture of S lactic acid.

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Let's take a look
at a carbohydrate,

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since Fischer used Fischer
projections for carbohydrates,

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specifically.

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So here I have a carbohydrate.

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And if I were to number
this carbohydrate,

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this carbonyl would
get a number 1.

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And then this would get
a number 2 over here,

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a number 4, and a number 4.

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This is a four-carbon
carbohydrate.

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How many stereoisomers does
this carbohydrate have?

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Well, this carbon number
2 is a chirality center.

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And carbon number 3
is a chirality center,

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so 2 chirality centers.

121
00:05:11,690 --> 00:05:14,360
So I use the formula
of 2 to the n,

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where n is the number
of chirality centers.

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So I would expect 2 squared,
or 4 possible stereoisomers

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for this molecule.

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So you could draw four
different stereoisomers

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for this molecule.

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We'll draw them
in a few minutes.

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For right now, I've gone
ahead and drawn one of them

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as a sawhorse projection.

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So here I have a sawhorse
projection of one

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of the possible stereoisomers.

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And what we're
going to do is we're

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going to put our
eye right up here.

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And we're going to stare
straight down at this bond

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right here.

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And we're going to see if
we can draw the Fischer

137
00:05:50,790 --> 00:05:52,350
projection for this molecule.

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So what do we see?

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Well, let's start with
this carbon right up here.

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So we'll make that
carbon this one.

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And you can see that the
OH attached to that carbon

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is going to the right.

143
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And it's going up at us.

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So that OH is going to the
right, and it's going up at us.

145
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And then if I look at
this hydrogen over here,

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it's on the left.

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And it's going up at us.

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So my hydrogen is on the
left and it's going up at us.

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And this aldehyde functional
group, this CHO, you can see

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00:06:29,500 --> 00:06:32,110
is going down.

151
00:06:32,110 --> 00:06:35,110
So this aldehyde functional
group is going away from us.

152
00:06:35,110 --> 00:06:37,170
So we can go ahead and
represent that aldehyde

153
00:06:37,170 --> 00:06:40,820
as going away from us
in space like that.

154
00:06:40,820 --> 00:06:44,080
Well, this chirality
center carbon

155
00:06:44,080 --> 00:06:47,280
is connected to this
chirality center carbon.

156
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So we'll go ahead and
draw a straight line,

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since we're looking
straight down at it.

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And once again, we will
find that our OH group

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00:06:53,610 --> 00:06:55,540
is on the right
coming out at us.

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Our hydrogen is on the
left coming out at us.

161
00:06:58,740 --> 00:07:00,700
So let's go ahead
and put those in.

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00:07:00,700 --> 00:07:02,890
OH group is on the
right coming out at us.

163
00:07:02,890 --> 00:07:05,230
Hydrogen is on the
left coming out at us.

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And then, of course, we
have this CH2OH down here

165
00:07:09,040 --> 00:07:10,620
as going away from us in space.

166
00:07:10,620 --> 00:07:14,670
So we'll go ahead and
draw that CH2OH going away

167
00:07:14,670 --> 00:07:15,860
from us in space like that.

168
00:07:15,860 --> 00:07:20,110
So that would be the Fischer
projection translated.

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Let's go ahead and make it into
an actual Fischer projection

170
00:07:22,690 --> 00:07:25,730
where we just go ahead
and draw straight lines.

171
00:07:25,730 --> 00:07:27,790
And the intersection
of those straight lines

172
00:07:27,790 --> 00:07:31,660
are where our
chirality centers are.

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So this would be an H.
This would be an OH.

174
00:07:35,310 --> 00:07:36,140
This would be an H.

175
00:07:36,140 --> 00:07:37,250
This would be an OH.

176
00:07:37,250 --> 00:07:39,050
This would be our CH2OH.

177
00:07:39,050 --> 00:07:42,350
And then at the top, we
have our aldehyde, CHO.

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So this is one of the four
possible stereoisomers.

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00:07:45,890 --> 00:07:47,890
And Fischer projections
just make it much easier

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00:07:47,890 --> 00:07:49,350
when we're working
with carbohydrates.

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00:07:49,350 --> 00:07:50,490
So this is one of the four.

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00:07:50,490 --> 00:07:52,450
Let's go ahead and redraw
the one we just drew

183
00:07:52,450 --> 00:07:55,702
and let's get the other three to
get our total of four on here.

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00:07:55,702 --> 00:07:58,160
So I'm going to take the one
that I just drew on the right.

185
00:07:58,160 --> 00:07:59,460
I'm going to redraw it.

186
00:07:59,460 --> 00:08:01,220
I'm going to draw it a little
bit smaller so everything

187
00:08:01,220 --> 00:08:02,055
will fit in here.

188
00:08:02,055 --> 00:08:06,030
So this is one
possible stereoisomer.

189
00:08:06,030 --> 00:08:08,910
I have my OHs on the right.

190
00:08:08,910 --> 00:08:10,900
I have my hydrogens.

191
00:08:10,900 --> 00:08:12,760
I have my CHO.

192
00:08:12,760 --> 00:08:13,456
I have my CH2OH.

193
00:08:13,456 --> 00:08:16,450


194
00:08:16,450 --> 00:08:19,560
If I wanted to draw the
enantiomer to this molecule,

195
00:08:19,560 --> 00:08:22,760
I would just have to
reflect it in a mirror.

196
00:08:22,760 --> 00:08:24,150
So I could just do this.

197
00:08:24,150 --> 00:08:27,190
I could reflect the
molecule in a mirror,

198
00:08:27,190 --> 00:08:29,730
and I would have the enantiomer.

199
00:08:29,730 --> 00:08:33,429
So this would be the
enantiomer to the stereoisomer

200
00:08:33,429 --> 00:08:35,470
that I just drew.

201
00:08:35,470 --> 00:08:38,289
If I wanted to
draw the other two,

202
00:08:38,289 --> 00:08:39,789
I can just go ahead
and real quickly

203
00:08:39,789 --> 00:08:42,179
put in my Fischer
projections right here.

204
00:08:42,179 --> 00:08:44,610
So I have two more to go.

205
00:08:44,610 --> 00:08:50,840
And I'm going to put the OH over
here, and then the H over here,

206
00:08:50,840 --> 00:08:54,650
and then the OH over
here, and the H over here.

207
00:08:54,650 --> 00:08:58,530
So this is yet another
possible stereoisomer.

208
00:08:58,530 --> 00:09:01,530
And I'll draw the mirror
image over here on the right.

209
00:09:01,530 --> 00:09:04,230
So I have to have a
hydrogen right here.

210
00:09:04,230 --> 00:09:06,850
And then my OH must
be on this side.

211
00:09:06,850 --> 00:09:11,420
And then I must have an
OH right here, and then

212
00:09:11,420 --> 00:09:14,975
a hydrogen on the other side,
and then a CHO for my aldehyde,

213
00:09:14,975 --> 00:09:17,200
and a CH2OH.

214
00:09:17,200 --> 00:09:20,420
So here I have my four
possible stereoisomers

215
00:09:20,420 --> 00:09:22,792
for this carbohydrate.

216
00:09:22,792 --> 00:09:24,500
And I'm going to go
ahead and label them.

217
00:09:24,500 --> 00:09:27,170
I'm going to label this
first one here stereoisomer

218
00:09:27,170 --> 00:09:31,760
A, stereoisomer B, stereoisomer
C, and stereoisomer D.

219
00:09:31,760 --> 00:09:34,860
Well, C and D are mirror
images of each other.

220
00:09:34,860 --> 00:09:37,169
So they are enantiomers
of each other.

221
00:09:37,169 --> 00:09:38,210
So these are enantiomers.

222
00:09:38,210 --> 00:09:40,820
A and B are mirror
images, so they

223
00:09:40,820 --> 00:09:42,790
are enantiomers to each other.

224
00:09:42,790 --> 00:09:45,600
And then we talked about
in the diastereomer video,

225
00:09:45,600 --> 00:09:51,170
if I took one of the ones from A
and B-- so let me just go ahead

226
00:09:51,170 --> 00:09:53,030
and circle that--
if I just took A.

227
00:09:53,030 --> 00:09:55,780
If I took one of the ones from
A and B and one of the ones

228
00:09:55,780 --> 00:09:58,000
from C and D, and
I'll just take C. Then

229
00:09:58,000 --> 00:10:00,930
A and C are diastereomers
of each other.

230
00:10:00,930 --> 00:10:04,910
They are non-superimposable,
non-mirror images

231
00:10:04,910 --> 00:10:05,570
of each other.

232
00:10:05,570 --> 00:10:07,750
So those are enantiomers
and diastereomers,

233
00:10:07,750 --> 00:10:11,349
to review what we covered
in an earlier video.

234
00:10:11,349 --> 00:10:13,390
Let's do one more thing
with Fischer projections.

235
00:10:13,390 --> 00:10:16,270
Let's assign absolute
configurations

236
00:10:16,270 --> 00:10:18,860
to one of the stereoisomers.

237
00:10:18,860 --> 00:10:20,780
So let's just choose
the first one, A.

238
00:10:20,780 --> 00:10:23,030
So we've been talking
about A. And let's go ahead

239
00:10:23,030 --> 00:10:24,930
and redraw it really fast.

240
00:10:24,930 --> 00:10:29,410
And let's see how can we figure
out the absolute configuration

241
00:10:29,410 --> 00:10:34,357
at my chirality centers
from a Fischer projection.

242
00:10:34,357 --> 00:10:36,440
So it just makes a little
bit trickier than usual.

243
00:10:36,440 --> 00:10:38,330
So here I have my
Fischer projection.

244
00:10:38,330 --> 00:10:40,250
And your aldehyde's
going to get a 1,

245
00:10:40,250 --> 00:10:44,232
and then 2, 3, 4 in terms of
numbering your carbon chain.

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00:10:44,232 --> 00:10:46,190
I want to figure out the
absolute configuration

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00:10:46,190 --> 00:10:47,650
at carbon 2 here.

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00:10:47,650 --> 00:10:49,930
So at carbon 2, what do I have?

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00:10:49,930 --> 00:10:52,060
I know a Fischer
projection tells me

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00:10:52,060 --> 00:10:55,760
that if it's a horizontal line,
everything is coming out at me.

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00:10:55,760 --> 00:10:57,430
So my OH is coming out at me.

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00:10:57,430 --> 00:10:59,950
And my hydrogen is
coming out at me.

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00:10:59,950 --> 00:11:03,620
Let's go back up here and stare
down that carbon 2 chirality

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00:11:03,620 --> 00:11:04,120
center.

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00:11:04,120 --> 00:11:06,760
And let's see what we would
actually see if we do that.

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00:11:06,760 --> 00:11:09,390
So here is carbon 2 right here.

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00:11:09,390 --> 00:11:12,640
I'm going to stare down
right here this time.

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00:11:12,640 --> 00:11:15,070
So I have my OH
coming out at me,

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00:11:15,070 --> 00:11:17,240
my hydrogen coming out at me.

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00:11:17,240 --> 00:11:19,280
That makes this
bond and this bond

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00:11:19,280 --> 00:11:22,030
to actually go away
from me in space.

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00:11:22,030 --> 00:11:24,050
So the aldehyde is
going to go away

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00:11:24,050 --> 00:11:27,010
from me in space like that.

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00:11:27,010 --> 00:11:29,629
So I'm going to go ahead
and draw my aldehyde.

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00:11:29,629 --> 00:11:31,920
Now, I'm actually going to
go ahead and show the carbon

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00:11:31,920 --> 00:11:33,140
bond to one hydrogen.

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00:11:33,140 --> 00:11:35,519
I know the carbon's double
bonded to an oxygen,

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00:11:35,519 --> 00:11:36,810
so I'm going to go and do that.

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00:11:36,810 --> 00:11:38,893
That was that trick we
learned in an earlier video

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00:11:38,893 --> 00:11:40,490
for assigning absolute
configuration.

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00:11:40,490 --> 00:11:41,948
And then the rest
of the molecule's

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00:11:41,948 --> 00:11:43,370
actually going down in space.

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00:11:43,370 --> 00:11:46,290
So this would be a carbon
here bonded to a hydrogen.

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00:11:46,290 --> 00:11:48,950
And this carbon is bonded
to an oxygen and a carbon.

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00:11:48,950 --> 00:11:50,690
So what is the
absolute configuration

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00:11:50,690 --> 00:11:51,720
of this carbon here?

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00:11:51,720 --> 00:11:56,990
Well, if I think about this
is my chirality center,

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00:11:56,990 --> 00:11:59,210
what are the atoms directly
attached to that carbon?

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00:11:59,210 --> 00:12:01,690
Well, I have a hydrogen,
a carbon, an oxygen,

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00:12:01,690 --> 00:12:02,320
and a carbon.

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00:12:02,320 --> 00:12:06,670
Well, immediately I know that
my oxygen is going to win.

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00:12:06,670 --> 00:12:09,980
So I can go ahead and assign
a number 1 to my oxygen right

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00:12:09,980 --> 00:12:10,650
here.

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00:12:10,650 --> 00:12:13,070
And then I think about
what's next priority.

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00:12:13,070 --> 00:12:15,800
Well, it would be
carbon versus carbon.

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00:12:15,800 --> 00:12:19,450
So at the top, I have
oxygen, oxygen, hydrogen.

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00:12:19,450 --> 00:12:22,410
The bottom carbon, I have
oxygen, carbon, hydrogen.

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00:12:22,410 --> 00:12:24,080
So we saw in an
earlier video, you

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00:12:24,080 --> 00:12:25,455
go for first point
of difference.

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00:12:25,455 --> 00:12:27,750
So oxygen versus
oxygen, no one wins.

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00:12:27,750 --> 00:12:30,280
Then I go oxygen versus
carbon, and oxygen wins.

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00:12:30,280 --> 00:12:32,160
So this would get
a number 2 up here.

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00:12:32,160 --> 00:12:34,430
And then this would get a
number 3 for my substituent.

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00:12:34,430 --> 00:12:36,380
And my hydrogen
would get a number 4.

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00:12:36,380 --> 00:12:38,340
So I'm going around this way.

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00:12:38,340 --> 00:12:42,500
I am going around this way,
if I ignore my hydrogen.

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00:12:42,500 --> 00:12:44,460
So I'm going counterclockwise.

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00:12:44,460 --> 00:12:48,400
So it looks like it's S.
But remember, the hydrogen

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00:12:48,400 --> 00:12:50,070
is actually coming out at me.

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00:12:50,070 --> 00:12:53,229
So in the little trick I showed
you in the earlier video,

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00:12:53,229 --> 00:12:55,520
if the hydrogen is coming
out at me, all you have to do

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00:12:55,520 --> 00:12:56,560
is reverse it.

303
00:12:56,560 --> 00:13:00,000
So it looks like it's S, but
since the hydrogen's coming out

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00:13:00,000 --> 00:13:02,710
at, me, I can go ahead
and say with certainty

305
00:13:02,710 --> 00:13:05,560
that it is R at that
chirality center.

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00:13:05,560 --> 00:13:09,730
So at carbon 2, at
this carbon, it is R.

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00:13:09,730 --> 00:13:13,190
So you can do the same thing
with the chirality center

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00:13:13,190 --> 00:13:14,540
at the third position.

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00:13:14,540 --> 00:13:17,130
So you could do the same
thing with this one.

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00:13:17,130 --> 00:13:20,380
And if you do that, you
will find that it is also R.

311
00:13:20,380 --> 00:13:23,090
So you could go ahead and
say for this carbohydrate,

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00:13:23,090 --> 00:13:27,730
it is R at carbon 2,
and it is R at carbon 3.

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00:13:27,730 --> 00:13:29,840
So it is 2R, 3R.

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00:13:29,840 --> 00:13:32,140
And there's a 2R,
3R stereoisomer.

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00:13:32,140 --> 00:13:35,930
And you could do that for
all four of the stereoisomers

316
00:13:35,930 --> 00:13:37,750
that we drew for
this carbohydrate.

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00:13:37,750 --> 00:13:40,580
And you could then compare
enantiomers and diastereomers

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00:13:40,580 --> 00:13:41,670
that way, as well.

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00:13:41,670 --> 00:13:44,570
So that's a quick summary
of Fischer projections.

320
00:13:44,570 --> 00:13:45,200
Practice.

321
00:13:45,200 --> 00:13:47,930
And use your molecular
model set to help you

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00:13:47,930 --> 00:13:50,530
with the visualization aspect.

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00:13:50,530 --> 00:13:51,296