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8/12/2019 26656310 Introduction to Organic Chemistry
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Introduction toIntroduction to
OrganicOrganicChemistryChemistry2 ed2 ed
William H. BrownWilliam H. Brown
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CarbohydratesCarbohydrates
Chapter 24
Chapter 16Chapter 16
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CarbohydratesCarbohydrates CarbohydrateCarbohydrate: a polyhydroxyaldehyde or
polyhydroxyketone, or a substance that givesthese compounds on hydrolysis
MonosaccharideMonosaccharide: a carbohydrate that cannot behydrolyzed to a simpler carbohydrate
monosaccharides have the general formula CCnnHH
2n2nOO
nn,
where nnvaries from 3 to 8
aldosealdose: a monosaccharide containing an aldehydegroup
ketoseketose: a monosaccharide containing a ketone group
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MonosaccharidesMonosaccharides monosaccharides are classified by their number of
carbon atoms
hexose
heptose
octose
triosetetrose
pentose
FormulaName
C3H6O3C4H8O4
C5H10 O5
C6H12 O6
C7H14 O7C8H16 O8
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MonosaccharidesMonosaccharides There are only two trioses
often aldo- and keto- are omitted and these compoundsare referred to simply as trioses
although this designation does not tell the nature of thecarbonyl group, it at least tells the number of carbons
Dihydroxyacetone(a ketotriose)
Glyceraldehyde(an aldotriose)
CHO
CHOH
CH2OH
CH2OH
C=O
CH2OH
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MonosaccharidesMonosaccharides Glyceraldehyde contains a stereocenter and
exists as a pair of enantiomers
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Fischer ProjectionsFischer Projections Fischer projectionFischer projection: a two dimensional
representation for showing the configuration oftetrahedral stereocenters
horizontal lines represent bonds projecting forward
vertical lines represent bonds projecting to the rear
(R)-Glyceraldehyde
CHO
CH OH
CH2OH
(R)-Glyceraldehyde
convert toa Fischer
projection H OH
CHO
CH2OH
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D,L MonosaccharidesD,L Monosaccharides In 1891, Emil Fischer made the arbitrary
assignments of D- and L- to the enantiomers ofglyceraldehyde
L-GlyceraldehydeD-Glyceraldehyde
[]25 = +13.5D
[ ]25 = -13.5D
CHO
CH2OH
OHHCHO
CH2OH
HHO
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Copyright 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, whenwritten as a Fischer projection, has the -OH on itspenultimate carbon on the right
L-monosaccharideL-monosaccharide: a monosaccharide that, whenwritten as a Fischer projection, has the -OH on itspenultimate carbon on the left
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Copyright 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
CHO
CH2OH
OHH
OHH
CHO
CH2OH
HHO
OHH
CHO
CH2OH
OHH
OHH
OHH
CHO
CH2OH
HH
OHH
OHH
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Copyright 2000 by John Wiley & Sons, Inc. All rights reserved.
D,L MonosaccharidesD,L Monosaccharides and the three most common D-aldohexoses
CHO
CH2OH
OHH
HHO
OHH
OHH
D-GlucosamineD-Glucose
D-Galactose
CHO
CH2OH
OHH
HHO
HHO
OHH
CHO
CH2OH
NH2H
HHO
HHO
OHH
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Copyright 2000 by John Wiley & Sons, Inc. All rights reserved.
Cyclic StructureCyclic Structure Monosaccharides have hydroxyl and carbonyl
groups in the same molecule and exist almostentirely as five- and six-membered cyclichemiacetals
anomeric carbonanomeric carbon: the new stereocenter resulting fromcyclic hemiacetal formation
anomersanomers: carbohydrates that differ in configuration attheir anomeric carbons
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Copyright 2000 by John Wiley & Sons, Inc. All rights reserved.
Haworth ProjectionsHaworth Projections Haworth projections
five- and six-membered hemiacetals are represented asplanar pentagons or hexagons, as the case may be,viewed through the edge
most commonly written with the anomeric carbon onthe right and the hemiacetal oxygen to the back right
the designation - means that -OH on the anomericcarbon is cis to the terminal -CH
2OH; - means that it
is trans
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D-Glucose
-D-Glucopyranose (-D-Glucose)
C
H OH
HHO
HOH
H
CH2 OH
OH
OH( )H OH
H
HO
H H
OH
H
CH2 OH
O
O
H
H
H OH
H
HO
HOH()
OH
H
CH2 OH
O
-D-Glucopyranose ( -D-Glucose)
+
anomericcarbon
5
5 5
5
CHO
CH2OH
OHH
HHO
OHH
OHH
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Copyright 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-
OOPyranFuran
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Copyright 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 representfuranoses
O
OH()H
HHO OH
H H
-D-Ribofuranose( -D-Ribose)
O
H
OH()H
HO OH
H H
-D-Ribofuranose(-D-Ribose)
HOCH2 HOCH2
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Copyright 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 chairconformation
-D-Glucopyranose(chair conformation)
O
CH2OH
HOHO
OHOH ()
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Copyright 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)
OCH2 OH
HOHO
OHOH ()
-D-Glucopyranose(Haworth projection)
H
H OH
HHO
H OH ()
OH
H
CH2OH
O
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Copyright 2000 by John Wiley & Sons, Inc. All rights reserved.
MutarotationMutarotation MutarotationMutarotation: the change in specific rotation that
occurs when the or forms of a carbohydrateare converted to an equilibrium mixture of the two
+80.2
+80.2
+52.8
+150.7
-D-galactose-D-galactose
[] afterMutarotation(degrees)
[]Monosaccharide
% Present atEquilibrium
28
72
64
36-D-glucose
-D-glucose+112.0
+18.7
+52.7
+52.7
(degrees)
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4
( -D-Galactose)( -D-Galactose) -D-Galactopyranose-D-Galactopyranose
D-Galactose
CH
OH
HO
HO
CH2 OH
OOH
OH ()OH
HO
HO
OCH2 OH
OCH2OH
HO
HO
OH OH ()
[ ]25 = +52.8D
[]25 = +150.7D
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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 isthe reference sweetness)
Monosaccharide& Disaccharides
Other CarbohydrateSweetening Agent
D-fructose 174
D-glucose 74D-galactose 0.22
sucrose (table sugar) 100
lactose (milk sugar) 0.16
honey 97
molasses 74corn syrup 74
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Copyright 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
CH2 OH
H
OH
OCH3()HHO
H
OHH
H
O
CH2 OH
HOHO
OHOCH3()
Haworth projectionChair conformation
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Copyright 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 followedby the name of the carbohydrate with the ending-eereplaced by -ideide
methyl -D-glucopyranoside
methyl -D-ribofuranoside
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Copyright 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 anamine to form an N-glycoside
N-glycosides of the following purine and pyrimidinebases 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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N-GlycosidesN-Glycosides
N
N N
N
NH2
HAdenine
anomericcarbon
a -N-glycosidebond
H
H
HOHOCH2
HO OH
NH2
O
N
N
H
HN
N N
N
O
H
H2N
Guanine
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Reduction to AlditolsReduction to Alditols The carbonyl group of a monosaccharide can be
reduced to an hydroxyl group by a variety ofreducing agents, including NaBH
4and H
2/M
Ni+
D-Glucitol(D-Sorbitol)
D-Glucose
H2
CHO
CH2OH
OHH
HHO
OHH
OHH
CH2
OH
CH2OH
OHH
HHO
OHH
OHH
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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,
Benedicts, or Fehlings solutions
Precipitates asa silver mirror
+
O
O
RCH
Ag(NH3)2+
RCO-
NH4+
Ag
Tollens' solution
NH3, H2O +
citrate ortartrate b!!er
Precipitatesas a red solid
++
O
C2+
RCO-
C2 O
ORCH
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Copyright 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
CH2OH
C=O
CH2OH
C-OH
CH2OH
CHOHCHOH
CH2OH
CHO
(CHOH)" (CHOH)" (CHOH)"
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Glucose AssayGlucose Assay The analytical procedure most often performed in
the clinical chemistry laboratory is thedetermination of glucose in blood, urine, or otherbiological fluid
this need arises because of the high incidence ofdiabetes in the population
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Glucose AssayGlucose Assay The glucose oxidase method is completely
specific for D-glucose
+
+
glucoseoxidase
D-Gluconic acid
Hydrogenperoxide
-D-GlucopyranoseOH
OHHO
HOCH2 OH
O
H2O2
O2 + H2OCO2H
CH2OH
OHH
HHO
OHHOHH
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Glucose AssayGlucose Assay O2is reduced to hydrogen peroxide H2O2
the concentration of H2O
2is proportional to the
concentration of glucose in the sample
in one procedure, hydrogen peroxide is used to oxidizeo-toluidine to a colored product, whose concentrationis determined spectrophotometrically
peroxidase +colored product+o-toluidine H2O2 H2O
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Ascorbic Acid (Vitamin C)Ascorbic Acid (Vitamin C) L-Ascorbic acid (vitamin C) is synthesized both
biochemically and industrially from D-glucoseCHO
CH2OH
OHH
HHO
OHH
OHH
D-Glucose
CH2 OH
OHH
HHO
O
OH
both biochemial
and industrialsyntheses
L-Ascorbic acid (Vitamin C)
O
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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 arefound in most body fluids
CH2 OH
OHH
H
HO
O
O
OH
CH2 OH
OHH
HO
OO
O
L-Ascorbic acid (Vitamin C)
L-Dehydroascorbic acid
oxidation
reduction
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MaltoseMaltose From malt, the juice of sprouted barley and other
cereal grains
O
OH
HOHO
CH2OH
O O
OH
HO
CH2OH
OH
-1,4-glycosidebond
-maltose becausethis -OH is beta
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-Maltose-Maltose
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LactoseLactose The principle sugar present in milk
about 5% - 8% in human milk, 4% - 5% in cows milk
O
OH
HO
OHCH2OH
O O
OH
HO
CH2OH
OH
-1,4-glycosidebond -lactose because
this -OH is beta
D-galactoseunit
D-glucoseunit
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-Lactose-Lactose
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SucroseSucrose Table sugar, from the juice of sugar cane and
sugar beet
O
OHHO
HO
CH2OH
O
-1,2-glycosidebond
D-glucopyranoseunit
O
CH2OH
HCH2OH
OH H
H HO
1
1
2
D-fructopyranoseunit
-2,1-glycosidebond
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Blood Group SubstancesBlood Group Substances Membranes of animal plasma cells have large
numbers of relatively small carbohydrates boundto them
these membrane-bound carbohydrates are part of themechanism by which cell types recognize each other;they act as antigenic determinantsantigenic determinants
among the first discovered of these antigenicdeterminants are the blood group substancesblood group substances
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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 thisclassification is a group of relatively small membrane-
bound carbohydrates
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ABO Blood ClassificationABO Blood Classification
NA#a$ #a$ NA#$Cell membraneof erythrocyte
-1,4-) -1,3-) -1-)
Fuc
-1,2-)NAGal = N-acetyl-D-galactosamine
Gal = D-galactose
NAGlu = N-acetyl-D-glucosamineFuc = L-fucose
missing intype O blood
D-galactose intype B blood
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L-FucoseL-Fucose L-fucose is synthesized biochemically from D-
glucose (see Problem 24.32)
CHO
OH
CH3
HHOOHH
H
HHO
An L-monosaccharide
because this -OH is onthe left in the Fischerprojection
rather than -CH2OH
Carbon 6 is -CH3
L-Fucose
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StarchStarch Starch is used for energy storage in plants
it can be separated into two fractions; amylose andamylopectin. Each on complete hydrolysis gives onlyD-glucose
amyloseamyloseis composed of continuous, unbranchedchains of up to 4000 D-glucose units joined by
-1,4-glycoside bonds
amylopectinamylopectinis a highly branched polymer of D-
glucose. Chains consist of 24-30 units of D-glucosejoined by -1,4-glycoside bonds and branches createdby -1,6-glycoside bonds
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GlycogenGlycogen The reserve carbohydrate for animals
a nonlinear polymer of D-glucose units joined by -1,4- and -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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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 fromchemically modified cellulose
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CarbohydratesCarbohydrates
End Chapter 16End Chapter 16