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Chemistry 2100
Lecture 9
Carbohydrates
• Molecular formula (CH2O)n
Carbohydrate:Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis.
Monosaccharide:Monosaccharide: A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.
Aldose:Aldose: A monosaccharide containing an aldehyde group.Ketose:Ketose: A monosaccharide containing a ketone group.
Enantiomers
Monosacharides
In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde.
– D-monosaccharide:D-monosaccharide: the -OH on its penultimate carbon is on the right in a Fischer projection.
– L-monosaccharide: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
Epimers
Hemiacetals and Hemiketals
Cyclization
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
Pyranoses and
Furanoses
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
O
CH2OH
OHOH
HOCH2
HO
O
HOHO
OHOH
CH2OH
-D(–)-fructofuranose -D(–)-fructopyranose
(Honey)
Chair Conformations• For pyranoses, the six-membered ring
is more accurately represented as a chair conformationchair conformation.
OCH2OH
HOHO
OHOH()
CHOH
HO
CH2OHOHHO
OHO
OH()HO
HO
CH2OHO
(-D-Glucose)
(-D-Glucose)
-D-Glucopyranose
-D-Glucopyranose
D-Glucose
anomericcarbon
Chain-ring Equilibrium and Reducing Sugars
The Glycosidic
Bond
Disaccharides
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
starch
• amylose
• amylopectin
• dextrins
starch
• amylose
• amylopectin
• dextrins
starch
• amylose
• amylopectin
• dextrins
(1,4)
starch
starch
• amylose
• amylopectin
• dextrins
(14)
starch
• amylose
• amylopectin
• dextrins
(16) (14)
starch
• amylose
• amylopectin
• dextrins
glycogen
β(1,4)
cellulose
Other Polymers
Chitin
Agar
Heparin
Lipids
Fatty Acids
COOH
oleic acid (mp 4°C)
stearic acid (mp 70°C)
COOH
Triacylglycerols
Saponification• Saponification: the base-promoted
hydrolysis of fats and oils in aqueous NaOH and produces glycerol and a mixture of fatty acid salts called soaps.
O
CH2OCR
CH2OCR
RCOCH
O
O
CH2OH
CH2OH
HOCH RCO-Na+
O
A triglyceride 1,2,3-Propanetriol(Glycerol, glycerin)
+
Sodium soaps
3saponification
anionic detergents
(-HOH)
sodium lauryl sulfate
S
O
O
O NaCH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2O
NaOHH2SO 4CH3(CH2)10CH2O S
O
O
OHCH3(CH2)10CH2OH
lauryl alcohol
Synthetic Detergents (syndets)
Hydrogenation
Hardening: The reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H2/transition metal catalyst, which converts a liquid triglyceride to a semisolid.
"partially hydrogenated vegetable oil"
+
COOH
COOH
COOH
H2 catalyst
• •
Complex Lipids
Figure 21.1 Schematic diagram of simple and complex lipids.
Membranes: Glycerophoshpolipids
Fluid Mosaic Model
Figure 21.2 The fluid mosaic model of membranes.
O
O
O
O
Other Lipids: Waxes
Sterols
Steroids RU-486
O
HO
C C CH3
Me2N
cholesterol
HO
progesterone
O
O testosterone
O
OH
estradiol
HO
OH
Low-Density Lipoprotein
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