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Carbohydrates
• Molecular formula (CH2O)n
Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis.
Monosaccharide: A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.
Aldose: A monosaccharide containing an aldehyde group.Ketose: A monosaccharide containing a ketone group.
Monosacharides
In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde.
– D-monosaccharide: the -OH on its penultimate carbon is on the right in a Fischer projection.
– L-monosaccharide: the -OH on its penultimate carbon is on the left in a Fischer projection.
L-GlyceraldehydeD-Glyceraldehyde
CHOCHO
H OH
CH2OH CH2OH
HHO
[]25 = +13.5°D
[]25 = -13.5°D
C
CH2OH
OHH
HO H
H OH
H
O HH
O
C
CH2OH
OHH
HO H
H OH
H O
H
H
O1
2
3
5
6
4
-D-glucose -D-glucoseD-glucose
1
2
3
5
6
4
1
2
3
5
6
4
C
CH2OH
OHH
HO H
H OH
H
OH H
O
Haworth ProjectionsD-Fructose (a 2-ketohexose) also forms a five-membered cyclic hemiacetal.
HO
HOCH2 OH
HHO
CH2OH
OHH
H
C=O
CH2OH
HOH
CH2OH
OHH
HO HOH
HOHOCH2
HO HCH2OH
OH
D-Fructose
1
2
5
5
5
1
2
2
()
-D-Fructofuranose(-D-Fructose)
-D-Fructofuranose(-D-Fructose)
()
1
Chair Conformations• For pyranoses, the six-membered ring
is more accurately represented as a chair conformation.
OCH2OH
HOHO
OHOH()
CHOH
HO
CH2OHOHHO
OHO
OH()HO
HO
CH2OHO
(-D-Glucose)
(-D-Glucose)
-D-Glucopyranose
-D-Glucopyranose
D-Glucose
anomericcarbon
SweetnessMonosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol.
Sweetness relative to sucrose:Carbohydrate
fructose
glucose
galactose
sucrose (table sugar)
lactose (milk sugar)
honey
SweetnessRelative to Sucrose
1.741.000.970.74
0.320.16
Artificial Sweetener
SweetnessRelative to Sucrose
maltose 0.33
saccharin 450acesulfame-K 200aspartame 180sucralose 600
CH2OH
CH3
O
RBC
O
OHOH
OH
O
AcNHHO
OOH
CH2OHH
O
H
O
O
H
NAGlu
Fuc
Gal
Type A
HO
CH2OH
OHO
H AcNH
NAGal
Blood Groups (14)
(12)
(13) AcNH
CH2OH
CH3
O
RBC
O
OHOH
OH
O
AcNHHO
OOH
CH2OHH
O
H
O
O
H
NAGlu
Fuc
Gal
HO
CH2OH
OHO
H
Blood Groups (14)
(12)
(13) AcNH
Type B
OH
Gal