1. Case Western Reserve University
Chapter 22
Carbohydrates
Organic Chemistry
4th Edition
Paula Yurkanis Bruice
Irene Lee
Case Western Reserve University
Cleveland, OH
©2004, Prentice Hall

2. Carbohydrates They have the molecular formulas Cn(H2O)n
Compounds that can be hydrolyzed to polyhydroxy
aldehydes or polyhydroxy ketones are also classified as
carbohydrates

3. Simple Carbohydrates Are Monosacharides
Complex carbohydrates contain two or more sugar units
linked together
disaccharides
oligosaccharides
polysaccharides
Polyhydroxy aldehydes are aldoses
Polyhydroxy ketones are ketoses

4. D and L notations are used to describe the configurations
of carbohydrates

6. Configurations of Aldoses
Aldotetroses have two asymmetric carbons and
four stereoisomers

7. Diastereomers that differ in configuration at only one
asymmetric carbon are called epimers

8. A ketose has one less asysmmetric carbon than aldoses, therefore they have fewer stereoisomers

9. Redox Reactions of Monosaccharides
The carbonyl of aldoses and ketoses can be reduced by
the carbonyl-group reducing agents

11. Oxidation The aldehyde groups can be oxidized by Br2
Ketones and alcohols cannot be oxidized by Br2

12. In a basic solution, ketoses are converted into aldoses

13. A strong oxidizing agent such as HNO3 can oxidize the
aldehyde and the alcohol groups

14. Osazone Formation Aldoses and ketoses react with three equivalents of
phenylhydrazine

15. The C-2 epimers of aldoses form identical osazones

16. Reaction of Ketoses with Phenylhydrazine

17. The carbon chain of an aldose can be increased by one
carbon in a Kiliani–Fischer synthesis

18. The Ruff degradation shortens an aldose chain by one
carbon

19. Preparation of the Calcium D-Gluconate for the Ruff Degradation

20. Cyclic Structure of Monosaccharides
Hemiacetal Formation
anomer
anomer
The specific rotation of pure a-D-glucose or b-D-glucose
changes over time to reach an equilibrium (mutarotation)

21. Note …
If an aldose can form a five- or six-membered ring, it will
exist predominantly as a cyclic hemiacetal
Six-membered rings are called pyranoses
Five-membered rings are called furanoses
A sugar with an aldehyde, a ketone, a hemiacetal, or
a hemiacetal group is a reducing sugar

22. The structures of cyclic sugars are best represented by
the Haworth projections
Haworth projections allow us to see the relative
orientation of the OH groups in the ring

23. Ketoses also exist predominantly in cyclic forms

24. b-D-Glucose Is More Stable
b-D-glucose is the predominant form at equilibrium

25. Acylation of Monosaccharides
The OH groups of monosaccharides show the chemistry
of typical alcohols

26. Alkylation of the OH Groups

27. Formation of Glycosides
The acetal (or ketal) of a sugar is called a glycoside

28. Mechanism of Glycoside Formation

29. Formation of an N-Glycoside

30. The Anomeric Effect
The formation of a glycoside favors the a-glucoside
product: the anomeric effect

31. Determination of Ring Size
Approach 1
The size of the ring can be determined from the structure
of the open-chain form

32. Determination of Ring Size
Approach 2
An acetal of the monosaccharide is oxidized with excess
HIO4
The a-hydroxyaldehyde formed from HIO4 oxidation is
further oxidized to formic acid and another aldehyde

33. Disaccharides Composed of two monosaccharide subunits hooked
together by an acetal linkage
In a-maltose, the OH group bonded to the anomeric
carbon is axial
Maltose is a reducing sugar

34. In cellobiose, the two subunits are hooked together by a
b-1,4’-glycosidic linkage
Cellobiose is a reducing sugar

35. In lactose, the two different subunits are joined by a
b-1,4’-glycosidic linkage
Lactose is a reducing sugar

36. The most common disaccharide is sucrose
Sucrose is not a reducing sugar

37. Polysaccharides
Amylose is a component of starch

38. Amylopectin is another polysaccharide component of
starch that has a branched structure

40. An example of a naturally occurring product derived from
carbohydrates

41. Blood type is determined by the nature of the sugar
bound to the protein on the surface of red blood cells