Chemistry 2100 - Bonham Chemistry

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Chemistry 2100
Lecture 9
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.
Enantiomers
Monosacharides
In 1891, Emil Fischer made the arbitrary
assignments of D- and L- to the enantiomers
of glyceraldehyde.
CHO
H
OH
CH2 OH
D-Glyce ral de h yde
25
[]D
= +13.5°
CHO
HO
H
CH2 OH
L-G lyce ral de h yde
25
[]D
= -13.5°
– D-monosaccharide: the -OH on its penultimate
carbon is on the right in a Fischer projection.
– L-monosaccharide: the -OH on its penultimate
Epimers
Hemiacetals and Hemiketals
Cyclization
H
1
O H
H
2
OH
HO
3
H
H
4
OH
H
5
C
6
CH 2 OH
-D-glucose
H
O
1
C
O
H O
1
H
H
2
OH
HO
3
H
OH
C
H
2
OH
HO
3
H
H
4
OH
H
4
H
5
O H
H
5
6
CH 2 OH
D-glucose
6
CH2 OH
-D-glucose
O
Pyranoses
and
Furanoses
Haworth Projections
D-Fructose (a 2-ketohexose) also forms
a five-membered cyclic hemiacetal.
HOCH2
5
1
O
H HO
CH2 OH
2
OH( )
H
HO
H
 -D -Fructofuranose
( - D -Fructos e)
1
CH2 OH
2
C=O
HO
H
H
OH
H 5 OH
CH2 OH
D -Fru ctose
HOCH2
5
O
H HO
H
OH ( )
2
CH2 OH
HO
H
1
 - D -Fru ctofu ran os e
(- D -Fructose)
HOCH2
O
HO
OH
OH
CH2 OH
-D(–)-fructofuranose
O
OH
HO
HO
OH
CH2 OH
-D(–)-fructopyranose
(Honey)
Chair Conformations
• For pyranoses, the six-membered ring is
more accurately represented as a chair
anomeric
conformation.
carbon
HO
HO
CH2 OH
O
OH()
OH
 -D -Glu copyran os e
( - D -Glucos e)
HO
HO
CH2 OH
OH
O
C
OH H
D -Glucos e
HO
HO
CH2 OH
O
HO
OH( )
- D -Glu copyran os e
(  - D -Glucose)
Chain-ring Equilibrium and Reducing
Sugars
The
Glycosidic
Bond
Disaccharides
Sweetness
Monosaccharides are colorless crystalline
solids, very soluble in water, but only slightly
soluble in ethanol.
Sweetness relative to sucrose:
Sw eetnes s
Relative to
Carb oh yd rate
Sucrose
fru ctose
1.74
su cros e (table su gar) 1.00
honey
0.97
glucose
0.74
maltos e
0.33
galactose
0.32
lactose (milk s ugar)
0.16
Sw eetnes s
Relative to
Artificial
Sw eeten er
Sucrose
saccharin
450
aces ulfame-K
200
asp artame
180
su cralos e
600
starch
starch
• amylose
• amylopectin
• dextrins
starch
• amylose
• amylopectin
• dextrins
starch
(1,4)
• amylose
• amylopectin
• dextrins
starch
(1,4)
• amylose
• amylopectin
• dextrins
starch
(1,6)
(1,4)
• amylose
• amylopectin
• dextrins
starch
• amylose
• amylopectin
• dextrins
glycogen
cellulose
β (1,4)
Other Polymers
Agar
Chitin
Heparin
Lipids
Fatty Acids
CO OH
oleic acid (mp 4°C)
CO OH
stearic acid (mp 70°C)
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
O CH2 OCR
RCOCH O
CH2 OCR
A triglyceride
saponification
CH2 OH
HOCH
CH2 OH
+
O
+
3RCO Na
1,2,3-Propanetriol Sod ium soaps
(Glycerol, glycerin)
Synthetic Detergents (syndets)
O
CH3 (CH2 )10 CH2 OH
laur yl alcohol
H2SO 4
( - HOH)
CH3 (CH2 )10 CH2 O
S OH
NaOH
O
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 O
sodium laur yl sulf at e
anionic detergents
O
S O Na
O
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.
H2
c atalyst
• +•
"partially hydrogenated vegetable oil"
CO OH
CO OH
CO OH
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.
Other Lipids: Waxes
O
O
O
O
Sterols
Steroids
Me2 N
HO
C C
O
RU-486
CH3
O
HO
O
c holeste rol
proge ste rone
OH
OH
HO
O
te st oste rone
e str adiol
Low-Density Lipoprotein
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