Fischer Projection

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Fischer Projection
representation of a 3D molecule as a flat structure where a tetrahedral carbon is represented as two crossed
lines.
vertical line is going back behind
of the plane of the page
carbon
C
substituent
horizonal line is coming out
of the plane of the page
CHO
CHO
H
OH
H
HOH2C
CHO
OH
H
CH2OH
OH
CH2OH
(R)-(+)-glyceraldehyde
Fischer projection
Manipulation of Fischer Projections:
1. Fischer Projection can be rotated by 180 ° only!
CHO
H
OH
CH2OH
180 ° rotation
HO
CH2OH
H
CHO
still
(R)-(+)-glyceraldehyde
(R)-(+)-glyceraldehyde
Rotation by 90 ° or -90 ° (270 °) invert the stereochemistry
CHO
H
90 ° rotation
OH
CH2OH
(R)-(+)-glyceraldehyde
H
HOH2C
OH
(S)-(-)-glyceraldehyde
CHO
H
OH
CH2OH
CHO
H
HOH2C
CHO
OH
These two compounds are enantiomers
Because of the convention of the
Fischer Projection (i.e., the
vertical lines are going back and
the horizonal lines are coming
forward) the 90° rotated Fisher
projection is actually the
enantiomer of the original
2. If one group of the Fischer projection is held steady, the other groups can be rotated either clockwise or
counter clockwise.
hold this group steady
CHO
H
OH
CHO
HOH2C
CH2OH
H
OH
still
(R)-(+)-glyceraldehyde
(R)-(+)-glyceraldehyde
Assigning R and S-configurations to Fischer projections
1. Assign priorities to the four substituents according to the Cahn-Ingold-Prelog convention.
2. Perform the two allowed manipulations of the Fischer projection to place the lowest priority group on
one of the vertical positions (either top or bottom)
3. If the priorities of the other three groups (1-2-3) proceed clockwise, the stereogenic center is assigned
as R. If the priorities of the other three groups (1-2-3) proceed counter clockwise, the stereogenic
center is assigned as S.
4
H
2
CHO
OH 1
4 H
CH2OH
lowest priority
group. Move to
a vertical position
hold one group
steady and rotate
the other three
CHO 2
1 HO
CH2OH
3
3
hold
steady
The priorities of the other three
groups (1-2-3) is clockwise. The
stereogenic center is assign as R
For more structures with more than one stereogenic center such as carbohydrates, the tetrahedral carbons
are "stacked" on top of one another.
OH
CHO
O
HO
HO
H
H
H
HO
OH
CH2OH
Threose
For carbohydrates, the convention is to put the carbonyl group at the top for aldoses and closest to the top
for ketoses. The carbons are numbered from top to bottom.
1 CHO
H
1 CH2OH
OH
HO
O
2
H
HO
H
H
OH
H
OH
H
OH
H
OH
CH2OH
CH2OH
D-Glucose
D-Fructose
Carbohydrates and amino acids are designated as D- or L- according to the stereochemistry of the highest
numbered carbon in the Fischer projection. If the hydroxyl group (or amino group for amino acids) is
pointing to the right in the Fischer Projection, the sugar (or amino acid) is designated as D. If the
hydroxyl group (or amino group for amino acids) is pointing to the left in the Fischer projection, the sugar
(or amino acid) is designated as L. Most naturally occurring carbohydrates are of the D-configuration
while most naturally occurring amino acids are L.
1 CHO
H 2 OH
3
HO
H
4
H
OH
highest numbered
stereogenic carbon
H 5
OH
1 CHO
H 2
OH
HO
3
HO 4
H
H
6 CH2OH
5 CH2OH
D-Glucose
L-Arabinose
highest numbered
stereogenic carbon
Converting Fischer Projections into Haworth Projections.
1. Identify the hydroxyl group which is cyclizing onto the carbonyl group. This hydroxy will become the
ring oxygen in the hemiacetal or hemiketal form of the carbohydrate. For D-glucose, it is the C5
hydroxyl in the pyranose form; for D-ribose, it is the C4-hydroxyl for the furanose form.
2. Manipulate the Fischer projection so this hydroxyl group is on the bottom.
3. Draw the Haworth projection so that the ring oxygen is on the top. For pyranoses, draw the sixmembered ring laying on it side with a oxygen at the upper right.
4. Substituents on the right side of the Fischer projection will be on the bottom face of the Haworth
projection. Substituents on the left side of the Fischer projection will be on the top face of the
Haworth projection.
5. Remember that in the cyclic form, the C1-hydroxyl group (the anomeric center) can usually adopt
either the up or down configuration.
T
T
T
O
T
T
B
B
B
B
O
T
B
T
B
B
1 CHO
OH
H
H
OH
H
H
OH
HOH2C
D-glucose
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
HOH2C
CH2OH
D-Ribose
Ring
oxygen
H
OH
OH
1
2
OH
H
1 CHO
O
5
OH
4
3
OH
Ring
oxygen
CHO
6 CH2OH
OH
HO
H
CH2OH
B
Pyranose
CHO
HO
T= top
B= bottom
T
B
Furanose
H
T
OH
β-D-glucopyranose
HO
4
6
OH
O
3
OH
2
OH
β-D-ribofuranose
1
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