26656310 Introduction to Organic Chemistry

8/12/2019 26656310 Introduction to Organic Chemistry

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16-1Copyright 2000 by John Wiley & Sons, Inc. All rights reserved.

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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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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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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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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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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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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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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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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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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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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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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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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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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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

26656310 Introduction to Organic Chemistry

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