26656310 introduction to organic chemistry (1)

8/3/2019 26656310 Introduction to Organic Chemistry (1)

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

Introduction toIntroduction toOrganic ChemistryOrganic Chemistry

2 ed2 ed

William H. BrownWilliam H. Brown


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CarbohydratesCarbohydratesChapter 16Chapter 16


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CarbohydratesCarbohydrates CarbohydrateCarbohydrate: a polyhydroxyaldehyde orpolyhydroxyketone, or a substance that gives these

compounds on hydrolysis

MonosaccharideMonosaccharide: a carbohydrate that cannot be hydrolyzedto 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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MonosaccharidesMonosaccharides monosaccharides are classified by their number of carbon atoms

hexose

heptose

octose

triose

tetrose

pentose

FormulaName

C3 H6 O3C4 H8 O4

C5 H10 O5

C6 H12 O6

C7 H14 O7C8 H16 O8


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MonosaccharidesMonosaccharides There are only two trioses

often aldo- and keto- are omitted and these compounds are referredto 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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MonosaccharidesMonosaccharides Glyceraldehyde contains a stereocenter and exists as a pairof enantiomers


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Fischer ProjectionsFischer Projections Fischer projectionFischer projection: a two dimensional representation forshowing 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

projection H OH

CHO

CH2 OH


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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

[E]25 = +13.5D

[E]25 = -13.5D

CHO

CH2 OH

OHH

CHO

CH2 OH

HHO


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D,L MonosaccharidesD,L Monosaccharides According to the conventions proposed by Fischer DD--monosaccharidemonosaccharide: a monosaccharide that, when written as a

Fischer projection, has the -OH on its penultimate carbon on the

right

LL--monosaccharidemonosaccharide: a monosaccharide that, when written as a

Fischer projection, has the -OH on its penultimate 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

CH2 OH

OHH

OHH

CHO

CH2 OH

HHO

OHH

CHO

CH2 OH

OHH

OHH

OHH

CHO

CH2 OH

HH

OHH

OHH


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D,L MonosaccharidesD,L Monosaccharides and the three most common D-aldohexosesCHO

CH2 OH

OHH

HHOOHH

OHH

D

-GlucosamineD-GlucoseD

-Galactose

CHO

CH2 OH

OHH

HHOHHO

OHH

CHO

CH2 OH

NH2H

HHOHHO

OHH


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Cyclic StructureCyclic Structure Monosaccharides have hydroxyl and carbonyl groups in thesame molecule and exist almost entirely as five- and six-

membered cyclic hemiacetals

anomeric carbonanomeric carbon: the new stereocenter resulting from cyclichemiacetal formation

anomersanomers: carbohydrates that differ in configuration at their

anomeric carbons


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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 designationF- means that -OH on the anomeric carbon is cis to

the terminal -CH2OH; E- means that it is trans


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D-Glucose

F-D-Glucopyranose

(F-D-Glucose)

C

H OH

HHO

HOH

H

CH2 OH

OH

OH( E)

H OH

H

HO

HH

OH

H

CH2 OH

O

O

H

H

H OH

H

HO

HOH(F)

OH

H

CH2 OH

O

E-D-Glucopyranose

(E-D-Glucose)

+

anomeric

carbon

5

5 5

5

CHO

CH2

OH

OHHHHO

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 Haworthprojections are adequate to represent furanoses

O

OH(E)

H

HHO OH

H H

E-D-Ribofuranose

(E-D-Ribose)

O

H

OH(F)

HHO OH

H H

F-D-Ribofuranose

(F-D-Ribose)

HOCH2 HOCH2


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Conformational FormulasConformational Formulas for pyranoses, the six-membered ring is more accuratelyrepresented as a strain-free chair conformation

F-D-Glucopyranose

(chair conformation)

OCH

2OH

HOHO

OHOH (F)


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Conformational FormulasConformational Formulas compare the orientations of groups on carbons 1-5 in the Haworthand chair representations of F-D-glucopyranose

in each case they are up-down-up-down-up

F-D-Glucopyranose

(chair conformation)

OCH2 OH

HOHO

OH OH (F)

F-D-Glucopyranose

(Haworth projection)

HH OH

HHO

HOH (F)

OH

H

CH2 OH

O


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MutarotationMutarotation MutarotationMutarotation: the change in specific rotation that occurswhen the E orF forms of a carbohydrate are converted to an

equilibrium mixture of the two

+80.2

+80.2

+52.8

+150.7

F-D-galactose

E-D-galactose

[E] afterMutarotation

(degrees)[E]

Monosaccharide% Present atEquilibrium

28

72

64

36E-D-glucose

F-D

-glucose

+112.0

+18.7

+52.7

+52.7

(degrees )


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4

(E-D-Galactose)

(F-D-Galactose) E-D-GalactopyranoseF-D-Galactopyranose

D-Galactose

CH

OH

HO

HO

CH2 OH

OOH

OH ( E)

OH

HO

HO

OCH2 OH

OCH2 OH

HO

HO

OHOH (F)

[E]25 = +52.8D

[E]25 = +150.7D


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Physical PropertiesPhysical Properties monosaccharides are colorless crystalline solids, very soluble inwater, but only slightly soluble in ethanol

following are relative sweetnesses (table sugar = 100 is the

reference sweetness)

Monosaccharide

& DisaccharidesOther 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 anomericcarbon is replaced by -OR

MethylF-D-glucopyranoside (methylF-D-glucoside)

O

CH2 OH

H

OH

OCH3 (F)H

HOH

OHH

H

OCH2 OHHOHO

OHOCH3 (F)

Haworth projection

Chair conformation


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GlycosidesGlycosides Glycoside bondGlycoside bond: the bond from the anomeric carbon of theglycoside 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 thecarbohydrate with the ending -ee replaced by -ideide

methylF-D-glucopyranoside

methyl E-D-ribofuranoside


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NN--GlycosidesGlycosides The anomeric carbon of a cyclic hemiacetal undergoesreaction with the N-H group of an amine to form an N-

glycoside

N-glycosides of the following purine and pyrimidine bases arestructural units of nucleic acids

HN

N

O

O

H

N

N

NH 2

O

H

HN

N

O

O

H

CH3

Uracil Thymine Cytosine


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NN--GlycosidesGlycosides

N

N N

N

NH2

HAdenine

anomericcarbon

a F-N-glycosidebond

HH

HOHOCH2

HO OH

NH2

O

N

N

H

HN

N N

N

O

HH2N

Guanine


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Reduction to AlditolsReduction to Alditols The carbonyl group of a monosaccharide can be reduced toan hydroxyl group by a variety of reducing agents, including

NaBH4 and H2/M

Ni+

D-Glucitol(D-Sorbitol)

D-Glucose

H2

CHO

CH2 OH

OHH

HHO

OHH

OHH

CH2 OH

CH2 OH

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 -CO2Hgroup 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 , H2 O+

citrate or

tartrate buffer

Precipitatesas a red solid

++

O

Cu2 +

RCO-

Cu2 O

O

RCH


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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

CH2 OH

C=O

CH2 OH

C-OH

CH2 OH

CHOH

CHOH

CH2 OH

CHO

(CH OH) n (CH OH) n(CH OH) n


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Glucose AssayGlucose Assay The analytical procedure most often performed in the clinicalchemistry laboratory is the determination of glucose in

blood, urine, or other biological fluid

this need arises because of the high incidence of diabetesin the population


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Glucose AssayGlucose Assay The glucose oxidase method is completely specific for D-

glucose

+

+

glucose

oxidase

D-Gluconic acid

Hydrogenperoxide

F-D-Glucopyranose

OHOH

HO

HOCH2 OH

O

H2 O2

O2 + H2O

CO2 H

CH2 OH

OHH

HHO

OHHOHH


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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 H2 O2 H2 O


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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-glucose

CHO

CH2

OH

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 are found in most

body fluids

CH2 OH

OHH

HHO

OO

OH

CH2 OH

OHH

H O

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

OHHO

HO

CH2

OH

OO

OHHO

CH2 OH

OH

E-1,4-glycoside

bond

F-maltose because

this -OH is beta


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FF--MaltoseMaltose


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LactoseLactose The principle sugar present in milk

about 5% - 8% in human milk, 4% - 5% in cows milk

O

OHHO

OHCH2 OH

OO

OH

HO

CH2 OH

OH

F-1,4-glycoside

bond F-lactose because

this -OH is beta

D-galactose

unitD-glucose

unit


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FF--LactoseLactose


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SucroseSucrose Table sugar, from the juice of sugar cane and sugar beet

O

OHHO

HO

CH2 OH

O

E-1,2-glycoside

bond

FD-glucopyranose

unit

O

CH2 OH

HCH2 OH

OH H

H

HO

1

1

2

FD-fructopyranoseunit

F-2,1-glycoside

bond


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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 antigenicantigenic

determinantsdeterminants

among the first discovered of these antigenic determinants 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 this classification is a

group of relatively small membrane-bound carbohydrates


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ABO Blood ClassificationABO Blood Classification

NAGal Gal NAGluCell membrane

of erythrocyte

E-1,4-) F-1,3-) F-1-)

Fuc

E-1,2-)

NAGal = N-acetyl-D-galactosamine

Gal = D-galactose

NAGlu = N-acetyl-D-glucosamineFuc = L-fucose

missing in

type O blood

D-galactose in

type B blood


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LL--FucoseFucose L-fucose is synthesized biochemically from D-glucose (see

Problem 24.32)

CHO

OH

CH3

HHO

OHH

H

HHO

An L-monosaccharide

because this -OH is onthe left in the Fischer

projection

rather than -CH 2OH

Carbon 6 is -CH 3

L-Fucose


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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 E-1,4-glycoside bonds

amylopectinamylopectin is a highly branched polymer of D-glucose. Chains

consist of 24-30 units of D-glucose joined by E-1,4-glycoside bonds

and branches created by E-1,6-glycoside bonds


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GlycogenGlycogen The reserve carbohydrate for animals

a nonlinear polymer of D-glucose units joined by E-1,4- and E-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 byF-

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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C i ht 2000 b J h Wil & S I All i ht d

CarbohydratesCarbohydrates

End Chapter 16End Chapter 16

26656310 introduction to organic chemistry (1)

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