16 16 16-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction Introduction to to Organic Organic Chemistry Chemistry 2 ed 2 ed William H. Brown William H. Brown
Dec 23, 2015
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16-1Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Introduction to Introduction to Organic Organic
ChemistryChemistry2 ed2 ed
William H. BrownWilliam H. Brown
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16-2Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
CarbohydratesCarbohydrates
Chapter 24
Chapter 16Chapter 16
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16-3Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
CarbohydratesCarbohydrates• CarbohydrateCarbohydrate: a polyhydroxyaldehyde or
polyhydroxyketone, or a substance that gives these compounds on hydrolysis
• MonosaccharideMonosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate• monosaccharides have the general formula CCnnHH2n2nOOnn,
where nn varies from 3 to 8• aldosealdose: a monosaccharide containing an aldehyde
group• ketoseketose: a monosaccharide containing a ketone group
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16-4Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
MonosaccharidesMonosaccharides• monosaccharides are classified by their number of
carbon atoms
hexose
heptose
octose
triose
tetrose
pentose
FormulaName
C3
H6
O3
C4
H8
O4
C5
H10
O5
C6
H12
O6
C7
H14
O7
C8
H16
O8
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16-5Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
MonosaccharidesMonosaccharides• There are only two trioses
• often aldo- and keto- are omitted and these compounds are referred to simply as trioses
• although this designation does not tell the nature of the carbonyl group, it at least tells the number of carbons
D ihydroxyacetone
(a ketotriose)
Glyceraldehyde
(an aldotriose)
CHO
CHOH
CH2
OH
CH2
OH
C=O
CH2
OH
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16-6Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
MonosaccharidesMonosaccharides• Glyceraldehyde contains a stereocenter and
exists as a pair of enantiomers
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16-7Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Fischer ProjectionsFischer Projections• Fischer projectionFischer projection: a two dimensional
representation for showing the configuration of tetrahedral stereocenters• horizontal lines represent bonds projecting forward • vertical lines represent bonds projecting to the rear
(R)-Glyceraldehyde
CHO
CH OH
CH2
OH
(R)-Glyceraldehyde
convert to
a Fischer
projectionH OH
CHO
CH2
OH
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16-8Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
D,L MonosaccharidesD,L Monosaccharides• In 1891, Emil Fischer made the arbitrary
assignments of D- and L- to the enantiomers of glyceraldehyde
L-GlyceraldehydeD-Glyceraldehyde
[ α ]25
= +13.5°D
[ α ]25
= -13.5°D
C H O
C H2
O H
O HH
C H O
C H2
O H
HH O
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16-9Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
D,L MonosaccharidesD,L Monosaccharides• According to the conventions proposed by
Fischer• D-monosaccharideD-monosaccharide: a monosaccharide that, when
written as a Fischer projection, has the -OH on its penultimate carbon on the right
• L-monosaccharideL-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the left
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16-10Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
• Following are • the two most common D-aldotetroses and • the two most common D-aldopentoses
D,L MonosaccharidesD,L Monosaccharides
D-Erythrose D-Threose D-Ribose 2-Deoxy-D-
ribose
C H O
C H2
O H
O HH
O HH
C H O
C H2
O H
HH O
O HH
C H O
C H2
O H
O HH
O HH
O HH
C H O
C H2
O H
HH
O HH
O HH
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16-11Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
D,L MonosaccharidesD,L Monosaccharides• and the three most common D-aldohexoses
C H O
C H 2 O H
O HH
HH O
O HH
O HH
D-GlucosamineD-Glucose D-Galactose
C H O
C H 2 O H
O HH
HH O
HH O
O HH
C H O
C H 2 O H
N H2
H
HH O
HH O
O HH
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16-12Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Cyclic StructureCyclic Structure• Monosaccharides have hydroxyl and carbonyl
groups in the same molecule and exist almost entirely as five- and six-membered cyclic hemiacetals• anomeric carbonanomeric carbon: the new stereocenter resulting from
cyclic hemiacetal formation• anomersanomers: carbohydrates that differ in configuration at
their anomeric carbons
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16-13Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Haworth ProjectionsHaworth Projections• Haworth projections
• five- and six-membered hemiacetals are represented as planar pentagons or hexagons, as the case may be, viewed through the edge
• most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right
• the designation - means that -OH on the anomeric carbon is cis to the terminal -CH2OH; α- means that it is trans
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16-14Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
D-Glucose
- -D Glucopyranose
( - - )D Glucose
C
H O H
H
H O
H
O H
H
C H2
O H
O H
O H ( α )
H O H
H
H O
HH
O H
H
C H2
O H
O
O
H
H
H O H
H
H O
H
O H ( β )
O H
H
C H2
O H
O
α -D-Glucopyranose
( α -D-Glucose)
+
anomeric
carbon
5
5 5
5
C H O
C H2
O H
O HH
HH O
O HH
O HH
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16-15Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Haworth ProjectionsHaworth Projections• six-membered hemiacetal rings are shown by the infix
-pyranpyran- • five-membered hemiacetal rings are shown by the infix
-furanfuran-
OO
PyranFuran
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16-16Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Conformational FormulasConformational Formulas• five-membered rings are close to being planar so that
Haworth projections are adequate to represent furanoses
O
O H ( α )
H
H
H O O H
H H
α -D-Ribofuranose
( α -D-Ribose)
O
H
O H ( β )
H
H O O H
H H
β -D-Ribofuranose
( β -D-Ribose)
H O C H2
H O C H2
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16-17Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Conformational FormulasConformational Formulas• for pyranoses, the six-membered ring is more
accurately represented as a strain-free chair conformation
- D-Glucopyranose
(chair conformation)
O
CH2
OH
HO
HO
OH
OH ( β )
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16-18Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Conformational FormulasConformational Formulas• compare the orientations of groups on carbons 1-5 in
the Haworth and chair representations of -D-glucopyranose
• in each case they are up-down-up-down-up
- -D Glucopyranose
( )chair conformation
O
C H 2 O H
H O
H O
O H
O H ( β )
β -D-Glucopyranose
(Haworth projection)
H
H O H
HH O
HO H ( β )
O H
H
C H2
O H
O
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16-19Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
MutarotationMutarotation• MutarotationMutarotation: the change in specific rotation that
occurs when the α or forms of a carbohydrate are converted to an equilibrium mixture of the two
+80.2
+80.2
+52.8
+150.7
- -D galactose
α - -D galactose
[ α ] after
Mutarotation
( )degrees
[ α ]
Monosaccharide
% Present at
Equilibrium
28
72
64
36α - -D glucose
- -D glucose
+112.0
+18.7
+52.7
+52.7
(degrees )
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16-20Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
44
4
( α - D-Galactose)
( β - D-Galactose) α - D-Galactopyranose
β - D-Galactopyranose
D-Galactose
C
HO H
H O
H O
C H 2 O H
O
O H
O H ( α )
O H
H O
H O
O
C H 2 O H
O
C H 2 O H
H O
H O
O HO H ( β )
[α ]25
= +52.8°D
[ α ]25
= +150.7°D
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16-21Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Physical PropertiesPhysical Properties• monosaccharides are colorless crystalline solids, very
soluble in water, but only slightly soluble in ethanol• following are relative sweetnesses (table sugar = 100 is
the reference sweetness)
Monosaccharide
& Disaccharides
Other Carbohydrate
Sweetening Agent
D-fructose 174
D-glucose 74
D-galactose 0.22
sucrose (table sugar) 100
lactose (milk sugar) 0.16
honey 97
molasses 74
corn syrup 74
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16-22Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Formation of GlycosidesFormation of Glycosides• GlycosideGlycoside: a carbohydrate in which the -OH of the
anomeric carbon is replaced by -OR
Methyl -D-glucopyranoside (methyl -D-glucoside)
O
C H2
O H
H
O H
O C H3
( )
H
H O
H
O HH
H
O
C H 2 O H
H O
H O
O H
O C H3
( )
Haworth projection
Chair conformation
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16-23Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
GlycosidesGlycosides• Glycoside bondGlycoside bond: the bond from the anomeric
carbon of the glycoside to an -OR group• Glycosides are named by listing the name of the
alkyl or aryl group attached to oxygen followed by the name of the carbohydrate with the ending -ee replaced by -ideide• methyl -D-glucopyranoside• methyl α-D-ribofuranoside
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16-24Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
N-GlycosidesN-Glycosides• The anomeric carbon of a cyclic hemiacetal
undergoes reaction with the N-H group of an amine to form an N-glycoside• N-glycosides of the following purine and pyrimidine
bases are structural units of nucleic acids
HN
N
O
O
H
N
N
NH2
O
H
HN
N
O
O
H
CH3
Uracil Thymine Cytosine
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16-25Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
N-GlycosidesN-Glycosides
N
N N
N
NH2
HAdenine
anomeric
carbon
a - -N glycoside
bond
H
H
H
OH O C H
2
H O O H
N H2
O
N
N
H
H N
NN
N
O
H
H2
N
Guanine
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16-26Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Reduction to AlditolsReduction to Alditols• The carbonyl group of a monosaccharide can be
reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2/M
Ni
+
D-Glucitol
(D-Sorbitol)
D-Glucose
H 2
C H O
C H2
O H
O HH
HH O
O HH
O HH
C H2
O H
C H2
O H
O HH
HH O
O HH
O HH
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16-27Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Oxidation to Aldonic AcidsOxidation to Aldonic Acids• Oxidation of the -CHO group of an aldose to a -
CO2H group can be carried out using Tollens’, Benedict’s, or Fehling’s solutions
Precipitates as
a silver mirror
+
O
O
R C H
A g ( N H3
)2
+R C O
- N H
4
+
A g
Tollens' solution
N H3
, H2
O+
citrate or
tartrate buffer
Precipitates
as a red solid
++
O
C u2 +
R C O-
C u2
O
O
R C H
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16-28Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Oxidation to Aldonic AcidsOxidation to Aldonic Acids• 2-Ketoses are also oxidized by these reagents
because, under the conditions of the oxidation, 2-ketoses equilibrate with isomeric aldoses
An aldoseAn enediolA 2-ketose
CH 2 OH
C=O
CH 2 OH
C-OH
CH 2 OH
CHOH
CHOH
CH2
OH
CHO
(CH OH)n
(CH OH)n
(CH OH)n
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16-29Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Glucose AssayGlucose Assay• The analytical procedure most often performed in
the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid
• this need arises because of the high incidence of diabetes in the population
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16-30Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Glucose AssayGlucose Assay• The glucose oxidase method is completely
specific for D-glucose
+
+
glucose
oxidase
D-Gluconic acid
Hydrogen
peroxide
- -D Glucopyranose
O H
O H
H O
H O
C H 2 O H
O
H 2 O 2
O 2 + H 2 O
C O2H
C H2O H
O HH
HH O
O HH
O HH
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16-31Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Glucose AssayGlucose Assay• O2 is reduced to hydrogen peroxide H2O2
• the concentration of H2O2 is proportional to the concentration of glucose in the sample
• in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometrically
peroxidase+colored product +o-toluidine H
2O
2H
2O
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16-32Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Ascorbic Acid (Vitamin C)Ascorbic Acid (Vitamin C)• L-Ascorbic acid (vitamin C) is synthesized both
biochemically and industrially from D-glucoseC H O
C H2
O H
O HH
HH O
O HH
O HH
D-Glucose
C H2
O H
O HH
H
H O
O
O H
both biochemial
and industrial
syntheses
L-Ascorbic acid
(Vitamin C)
O
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16-33Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Ascorbic Acid (Vitamin C)Ascorbic Acid (Vitamin C)• L-ascorbic acid is very easily oxidized to L-
dehydroascorbic acid. • both compounds are physiologically active and are
found in most body fluids
C H2
O H
O HH
H
H O
O
O
O H
C H2
O H
O HH
H
O
O
O
O
L-Ascorbic acid
(Vitamin C)
L-Dehydroascorbic acid
oxidation
reduction
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16-34Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
MaltoseMaltose• From malt, the juice of sprouted barley and other
cereal grains
O
O H
H O
H O
C H2
O H
OO
O H
H O
C H2
O H
O H
α -1,4-glycoside
bond
β -maltose because
this -OH is beta
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16-35Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
-Maltose-Maltose
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16-36Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
LactoseLactose• The principle sugar present in milk
• about 5% - 8% in human milk, 4% - 5% in cow’s milk
O
OH
HO
OH
CH2
OH
OO
OH
HO
CH2
OH
OH
-1,4-glycoside
bond
β -lactose because
this -OH is beta
D-galactose
unitD-glucose
unit
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16-37Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
-Lactose-Lactose
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16-38Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
SucroseSucrose• Table sugar, from the juice of sugar cane and
sugar beet
O
OH
HO
HO
CH2
OH
O
α -1,2-glycoside
bond
β− D-glucopyranose
unit
O
CH 2 OH
HCH
2OH
OH H
HHO
1
1
2
β− D-fructopyranose
unit
β -2,1-glycoside
bond
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16-39Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Blood Group SubstancesBlood Group Substances• Membranes of animal plasma cells have large
numbers of relatively small carbohydrates bound to them• these membrane-bound carbohydrates are part of the
mechanism by which cell types recognize each other; they act as antigenic determinantsantigenic determinants
• among the first discovered of these antigenic determinants are the blood group substancesblood group substances
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16-40Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ABO Blood ClassificationABO Blood Classification• In the ABO system, individuals are classified
according to four blood types: A, B, AB, and O• at the cellular level, the biochemical basis for this
classification is a group of relatively small membrane-bound carbohydrates
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16-41Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
ABO Blood ClassificationABO Blood Classification
NAGal Gal NAGluCell membrane
of erythrocyte
(α -1,4-) ( -1,3-) ( -1-)
Fuc
(α -1,2-)
= - - -NAGal N acetyl D galactosamine
= -Gal D galactose
= - - -NAGlu N acetyl D glucosamine
= -Fuc L fucose
missing in
type O blood
- D galactose in
type B blood
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16-42Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
L-FucoseL-Fucose• L-fucose is synthesized biochemically from D-
glucose (see Problem 24.32)
C H O
O H
C H3
HH O
O HH
H
HH O
An L-monosaccharide
because this -OH is on
the left in the Fischer
projection
rather than -CH2
OH
Carbon 6 is -CH3
L-Fucose
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16-43Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
StarchStarch• Starch is used for energy storage in plants
• it can be separated into two fractions; amylose and amylopectin. Each on complete hydrolysis gives only D-glucose
• amyloseamylose is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by α-1,4-glycoside bonds
• amylopectinamylopectin is a highly branched polymer of D-glucose. Chains consist of 24-30 units of D-glucose joined by α-1,4-glycoside bonds and branches created by α-1,6-glycoside bonds
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16-44Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
GlycogenGlycogen• The reserve carbohydrate for animals
• a nonlinear polymer of D-glucose units joined by α-1,4- and α-1,6-glycoside bonds bonds
• the total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle
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16-45Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
CelluloseCellulose• Cellulose is a linear polymer of D-glucose units
joined by -1,4-glycoside bonds• it has an average molecular weight of 400,000,
corresponding to approximately 2800 D-glucose units per molecule
• Both rayon and acetate rayon are made from chemically modified cellulose
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16-46Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
CarbohydratesCarbohydrates
End Chapter 16End Chapter 16