1. Chapter 23 Carbohydrates and Nucleic Acids
Organic Chemistry, 5th Edition L. G. Wade, Jr.
Chapter 23 Carbohydrates and Nucleic Acids
Jo Blackburn
Richland College, Dallas, TX
Dallas County Community College District
ã 2003, Prentice Hall

2. Carbohydrates
Synthesized by plants using sunlight to convert CO2 and H2O to glucose and O2.
Polymers include starch and cellulose.
Starch is storage unit for solar energy.
Most sugars have formula Cn(H2O)n, “hydrate of carbon.” =>
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3. Classification of Carbohydrates
Monosaccharides or simple sugars
polyhydroxyaldehydes or aldoses
polyhydroxyketones or ketoses
Disaccharides can be hydrolyzed to two monosaccharides.
Polysaccharides hydrolyze to many monosaccharide units. E.g., starch and cellulose have > 1000 glucose units =>
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4. Monosaccharides Classified by: aldose or ketose
number of carbons in chain
configuration of chiral carbon farthest from the carbonyl group
fructose, a
D-ketohexose
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glucose, a
D-aldohexose
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5. D and L Sugars
D sugars can be degraded to the dextrorotatory (+) form of glyceraldehyde.
L sugars can be degraded to the levorotatory (-) form of glyceraldehyde.
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6. The D Aldose Family
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7. Erythro and Threo
Terms used for diastereomers with two adjacent chiral C’s, without symmetric ends.
For symmetric molecules, use meso or d,l.
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8. Epimers
Sugars that differ only in their stereochemistry at a single carbon.
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9. Cyclic Structure for Glucose
Glucose cyclic hemiacetal formed by reaction of -CHO with -OH on C5.
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D-glucopyranose
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10. Cyclic Structure for Fructose
Cyclic hemiacetal formed by reaction of C=O at C2 with -OH at C5.
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D-fructofuranose
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11. Anomers
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12. Mutarotation Glucose also called dextrose; dextrorotatory. =>
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13. Epimerization
In base, H on C2 may be removed to form enolate ion. Reprotonation may change the stereochemistry of C2.
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14. Enediol Rearrangement
In base, the position of the C=O can shift. Chemists use acidic or neutral solutions of sugars to preserve their identity.
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15. Reduction of Simple Sugars
C=O of aldoses or ketoses can be reduced to C-OH by NaBH4 or H2/Ni.
Name the sugar alcohol by adding -itol to the root name of the sugar.
Reduction of D-glucose produces D-glucitol, commonly called D-sorbitol.
Reduction of D-fructose produces a mixture of D-glucitol and D-mannitol =>
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16. Oxidation by Bromine
Bromine water oxidizes aldehyde, but not ketone or alcohol; forms aldonic acid.
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17. Oxidation by Nitric Acid
Nitric acid oxidizes the aldehyde and the terminal alcohol; forms aldaric acid.
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18. Oxidation by Tollens Reagent
Tollens reagent reacts with aldehyde, but the base promotes enediol rearrangements, so ketoses react too.
Sugars that give a silver mirror with Tollens are called reducing sugars.
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19. Nonreducing Sugars
Glycosides are acetals, stable in base, so they do not react with Tollens reagent.
Disaccharides and polysaccharides are also acetals, nonreducing sugars.
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20. Formation of Glycosides
React the sugar with alcohol in acid.
Since the open chain sugar is in equilibrium with its - and -hemiacetal, both anomers of the acetal are formed.
Aglycone is the term used for the group bonded to the anomeric carbon.
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21. Ether Formation
Sugars are difficult to recrystallize from water because of their high solubility.
Convert all -OH groups to -OR, using a modified Williamson synthesis, after converting sugar to acetal, stable in base.
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22. Ester Formation
Acetic anhydride with pyridine catalyst converts all the oxygens to acetate esters.
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23. Osazone Formation Both C1 and C2 react with phenylhydrazine. =>
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24. Ruff Degradation
Aldose chain is shortened by oxidizing the aldehyde to -COOH, then decarboxylation.
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25. Kiliani-Fischer Synthesis
This process lengthens the aldose chain.
A mixture of C2 epimers is formed.
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26. Fischer’s Proof
Emil Fischer determined the configuration around each chiral carbon in D-glucose in 1891, using Ruff degradation and oxidation reactions.
He assumed that the -OH is on the right in the Fischer projection for D-glyceraldehyde.
This guess turned out to be correct! =>
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27. Determination of Ring Size
Haworth determined the pyranose structure of glucose in 1926.
The anomeric carbon can be found by methylation of the -OH’s, then hydrolysis.
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28. Periodic Acid Cleavage
Periodic acid cleaves vicinal diols to give two carbonyl compounds.
Separation and identification of the products determine the size of the ring.
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29. Disaccharides Three naturally occurring glycosidic linkages:
1-4’ link: The anomeric carbon is bonded to oxygen on C4 of second sugar.
1-6’ link: The anomeric carbon is bonded to oxygen on C6 of second sugar.
1-1’ link: The anomeric carbons of the two sugars are bonded through an oxygen. =>
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30. Cellobiose Two glucose units linked 1-4’. Disaccharide of cellulose.
A mutarotating, reducing sugar.
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31. Maltose
Two glucose units linked 1-4’.
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32. Lactose Galactose + glucose linked 1-4’. “Milk sugar.” =>
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33. Gentiobiose Two glucose units linked 1-6’.
Rare for disaccharides, but commonly seen as branch point in carbohydrates.
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34. Sucrose Glucose + fructose, linked 1-1’ Nonreducing sugar =>
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35. Cellulose Polymer of D-glucose, found in plants.
Mammals lack the -glycosidase enzyme.
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36. Amylose Soluble starch, polymer of D-glucose.
Starch-iodide complex, deep blue.
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37. Amylopectin
Branched, insoluble fraction of starch.
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38. Glycogen
Glucose polymer, similar to amylopectin, but even more highly branched.
Energy storage in muscle tissue and liver.
The many branched ends provide a quick means of putting glucose into the blood =>
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39. Chitin Polymer of N-acetylglucosamine. Exoskeleton of insects. =>
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40. =>
Nucleic Acids
Polymer of ribofuranoside rings linked by phosphate ester groups.
Each ribose is bonded to a base.
Ribonucleic acid (RNA)
Deoxyribonucleic acid (DNA)
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41. Ribonucleosides
A -D-ribofuranoside bonded to a heterocyclic base at the anomeric carbon.
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42. Ribonucleotides
Add phosphate at 5’ carbon.
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43. Structure of RNA
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44. Structure of DNA -D-2-deoxyribofuranose is the sugar.
Heterocyclic bases are cytosine, thymine (instead of uracil), adenine, and guanine.
Linked by phosphate ester groups to form the primary structure =>
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45. Base Pairings
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46. Double Helix of DNA
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Two complementary polynucleotide chains are coiled into a helix.
Described by Watson and Crick, 1953.
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47. DNA Replication
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48. Additional Nucleotides
Adenosine monophosphate (AMP), a regulatory hormone.
Nicotinamide adenine dinucleotide (NAD), a coenzyme.
Adenosine triphosphate (ATP), an energy source =>
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49. End of Chapter 23
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