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www.angelo.edu/faculty/kboudreawww.angelo.edu/faculty/kboudreaMr. Kevin A. BoudreauxMr. Kevin A. BoudreauxAngelo State UniversityAngelo State University
Fundamentals of Organic ChemistryFundamentals of Organic Chemistry^ CHEM 2353CHEM 2353
CarbohydratesCarbohydrates
Organic and Biochemistry for Today (4Spencer L. Seager / Michael R. Slabaugh th^ ed.)
- Carbohydrates are compounds of tremendous Carbohydrates and Biochemistry^ Carbohydrates and Biochemistry
biological importance:– they provide energy through oxidation
- they supply carbon for the synthesis of cellcomponents
- they serve as a form of stored chemical energy– they form part of the structures of some cells and
- Carbohydrates, along with lipids, proteins, nucleictissues
acids, and other compounds are known as biomolecules because they are closely associated
with living organisms.the chemistry of biomolecules and living organisms. Biochemistry is the study of
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Classification of Classification of CarbohydratesCarbohydrates
- Carbohydrates Carbohydrates^ Carbohydrates are polyhydroxy aldehydes or
ketones, or substances that yield such compounds onhydrolysis
C
H C O
HH C OHOH
H CCH OH
ribose^2 OH The term “carbohydrate” comes from the fact thatwhen you heat sugars, youget carbon and water.
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The Stereochemistry The Stereochemistry of Carbohydratesof Carbohydrates
- Glyceraldehyde, the simplest carbohydrate, exists in Stereoisomers^ Stereoisomers
two isomeric forms that are mirror images of eachother:
C
CHO
CH 2 OH
HO H H C OH
CH 2 OH
CHO
L-glyceraldehyde D-glyceraldehyde
- • These forms areGlyceraldehyde is a stereoisomers chiral molecule — it cannot be of each other.
superimposed on its mirror image. The two mirror-image forms of glyceraldehyde are enantiomers of
each other.
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- Chiral molecules have the same relationship to each Chiral Carbons^ Chiral Carbons
other that your left and right hands have whenreflected in a mirror.
- Achiral images — for example, drinking glasses, spheres, objects can be superimposed on the mirror
- and cubes.Any carbon atom which is connected to four
different groups nonsuperimposable mirror images; it is a will be chiral, and will have two chiral
carbon – if any or a of the two groups on the carbon are the center of chirality.
- Many organic compounds, including carbohydrates,same, the carbon atom cannot be chiral.
contain more than one chiral carbon.
- Identify the chiral carbon atoms (if any) in each of Examples: Chiral Carbon Atoms^ Examples: Chiral Carbon Atoms
the following molecules:
CH 3 C CH 3
OH
H CH^3 C CH^2 CH^3
OH
H
CH 3 CO^ CH 2 CH 3 O
HO
CH 3 C CH 2 Cl
OH
H
HO
H CH H
H
H CCl H Cl
H CCl Cl Cl
H CBr Cl F
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- Fischer projections^ Fischer ProjectionsFischer Projections are a convenient way to
- represent mirror images in two dimensions.Place the carbonyl group at or near the top and the
last achiral CH 2 OH at the bottom.
CCHO
CH 2 OH
HO H H C OH
CH 2 OH
CHO
CHO
CH 2 OH
HO H H OH
CH 2 OH
CHO
L -glyceraldehyde D -glyceraldehyde
- When there is more than one chiral center in a Naming Stereoisomers^ Naming Stereoisomers
carbohydrate, look at the chiral carbon farthest fromthe carbonyl group: if the hydroxy group points toright when the carbonyl is “up” it is the D-isomer,
and when the hydroxy group points to the left, it isthe L-isomer.
HO CHOH H CHOOH
HO L-erythrose (^) CH 2 OHH H D-erythroseCH 2 OH OH
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- Draw Fischer projections Examples: Fischer Projections^ Examples: Fischer Projections
of D and L lactic acid:
CH 3 CHCO^2 HOH
- Draw Fischer projectionsof D and L alanine: CH 3 CHNH^2 CO 2 H - Given the structurefor D-glucose, draw
the structure of L-glucose:
CHO
HOH OHH
H OH
CH 2 OH
H OH
D-glucose
- Identify the following compounds as D or L Examples: Fischer Projections^ Examples: Fischer Projections
isomers, and draw their mirror images.
HO H
C
H OH
CH 2 OH
H OH
CH 2 OHO
fructose
HO H
H CH 2 OHOH
H
CHO
lyxose
HO
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Monosaccharides Monosaccharides
- The monosaccharides are the simplest of the Classification of Monosaccharides^ Classification of Monosaccharides
carbohydrates, since they contain only onepolyhydroxy aldehyde or ketone unit.
- Monosaccharides are classified according to thenumber of carbon atoms they contain:
- The presence of an aldehyde is indicated by theprefix aldo- and a ketone by the prefix keto-.
carbons^ No. of^ MonosaccharideClass of
34 tetrosetriose
56 pentosehexose
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- Thus, glucose is an Classification of Monosaccharides^ Classification of Monosaccharides aldohexose (aldehyde + 6 Cs)
and ribulose is a ketopentose (ketone + 5 Cs)
CC
O H
H OH
HO CC H
C
H OH
CH 2 OH
H OH
an aldohexose^ glucose
C
CH 2 OH
H C OOH
CCH
2 OH
H OH
a ketopentose^ ribulose
-^ Examples: Classifying MonosaccharidesExamples: Classifying Monosaccharides Classify the following monosaccharides:
C
CH 2 OH
H CH 2 OHOH
O
CHO
HO CH 2 OHH
HO H C
CH 2 OH
H OHO
CH 2 OH
HO H
CHO
HOHO HH
CH 2 OH
H OH
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The Family of DThe Family of D- (L-forms not shown) -ketosesketoses DihydroxyacetoneCHCH^22 O^ OH^ OH^ Ketotriose^2 0 = 1 CH (^2) O OH D-erythruloseH CH^2 OHOH^ Ketotetroses^21 = 2 CH 2 OHO H OH H CH 2 OHOH
CH 2 OHO HO H D-ribulose H^ D-xyluloseCH^2 OHOH
Ketopentoses 22 = 4
The Family of DThe Family of D- (L-forms not shown) -ketosesketoses CH 2 OHO HOH^ OHH H CH 2 OHOH
CH 2 OHO HH OHOH H CH 2 OHOH
CH 2 OHO HOH HOH H CH 2 OHOH
CH 2 OHO HOHO HH D-Psicose D-Fructose D-Sorbose HD-TagatoseCH^2 OHOH
Ketohexoses 2 3 = 8
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- Physical Properties of Monosaccharides^ Physical Properties of Monosaccharides Most monosaccharides have a sweet taste (fructose
- is sweetest; 73% sweeter than sucrose).They are solids at room temperature.
- They are– Despite their high molecular weights, the extremely soluble in water:
presence of large numbers of OH groups makethe monosaccharides much more water soluble
- Glucose can dissolve in minute amounts of waterthan most molecules of similar MW.
to make a syrup (1 g / 1 ml H2O).
Fructose 1.73 Monosaccharide 28
Invert sugarSucrose 1.301.00 Mixture of glucose and fructoseDisaccharide
GlucoseXylose 0.740.40 MonosaccharideMonosaccharide
MaltoseGalactose 0.320.22 DisaccharideMonosaccharide
Lactose 0.16 Disaccharide^ Type
Sugar SweetnessRelative
Physical Properties of Monosaccharides Physical Properties of Monosaccharides Table 7.2 The relative sweetness of sugars(sucrose = 1.00)
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- Fructose closes on itself to form a^ Fructose AnomersFructose Anomers furanose ring : O a furanose ring
CH 2 OH O H O CH 2 OH OH
OH
CH 2 OHO OH
HO
CH 2 OH OH
CH 2 OHO OH
HO
OH CH 2 OH
D-fructose
α-D-fructose β-D-fructose
α-hydroxy
β-hydroxy
- Drawing Furanose and Pyranose Rings^ Drawing Furanose and Pyranose Rings Monosaccharides are often represented using the
Haworth structures shown below for furanose andpyranose rings.
- The remaining OH groups on the ring point up ordown depending on the identity of the sugar.
CH 2 OH O (^) O
CH 2 OH
Furanosering Pyranosering
always above ringfor D-saccharides
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Examples: Anomers Examples: Anomers
- Identify the structures below as being theforms, and draw the structure of their anomers: α- or β- CH 2 OH^ OH OH OH
O
ribose
OH O
OH OH OH
CH 2 OH
galactose
With Friends Like These, Who Needs Anomers?
- Aldehydes and ketones that have an OH group on Oxidation of Monosaccharides^ Oxidation of Monosaccharides
the carbon next to the carbonyl group react with abasic solution of Cua red-orange precipitate of copper(I) oxide (Cu 2+ ( Benedict’s reagent ) to form
- Sugars that undergo this reaction are called^2 O).
reducing sugars reducing sugars.). (All of the monosaccharides are
Reducing sugar + (^) deep blue Cu 2+^ oxidationproduct + Cu 2 O solution red-orangeppt
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- Once the glycoside is formed, the ring can no longer Glycoside Formation^ Glycoside Formation
open up to the open-chain form. Glycosides,therefore, are not reducing sugars.
Glycoside + Cu2+^ NR
- Identify the glycosidic linkage in each of the^ Examples: Glycoside FormationExamples: Glycoside Formation
following molecules:
OHCH^2 OH^ O
OHOCH^2 CH^3
OH CH^2 OH
OH OH
O
CH 2 OH
OCH 3
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Important MonosaccharidesImportant Monosaccharides CH 2 OH O OH
OH
Forms the sugar backbone of^ β -D-ribose OH ribonucleic acid ( RNA )
CH 2 OH O
OH
OH
deoxyribonucleic acid^ Forms the sugar backbone of^ β -D-deoxyribose ( DNA ) O
CH 2 OH
OH
OH
OH
Incorporated with glucoseinto lactose (milk sugar)^ β -D-galactose
OH
Important MonosaccharidesImportant Monosaccharides O
CH 2 OH
OH
OH
OH
OH
Also known as sugar ; present in honey and fruits.^ β -D-glucose dextrose and blood Glucose is metabolized in the bodyfor energy. Other sugars absorbedinto the body must be converted to glucose by the liver.
CH 2 OH O
OH
HO
OH
CH 2 OH
sugar^ Also known as. Fructose is the sweetest of^ β -D-fructose^ levulose^ and^ fruit the monosaccharides. It is presentin honey (1:1 ratio with glucose),fruits, and corn syrup. It is often used to sweeten foods, since lessfructose is needed to achieve thesame degree of sweetness.
