The document discusses the cyclic structures of glucose and fructose and how they form hemiacetals. It explains that glucose forms D-glucopyranose and fructose forms D-fructofuranose. It also discusses anomers, mutarotation, and how glucose and fructose can interchange between alpha and beta forms. The document then covers various reactions of monosaccharides including glycoside formation, Koenigs-Knorr reaction, ester and ether formation, and oxidation reactions like bromine oxidation to form aldonic acids and nitric acid oxidation to form aldaric acids. It concludes by discussing non-reducing sugars and chain shortening/lengthening reactions like R

1. Carbohydrates: PART B

2. Chapter 23 2
Cyclic Structure for Glucose
Glucose cyclic hemiacetal formed by reaction of -CHO with -OH on C5.
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D-glucopyranose

3. Chapter 23 3
Cyclic Structure for Fructose
Cyclic hemiacetal formed by reaction of C=O at C2 with -OH at C5.
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D-fructofuranose

4. Chapter 23 4
Anomers:
The C-1 position is called an anomeric carbon and the stereoisomers are called anomers because
when the glucose or fructose unit is closed to a hemiacetal two diff. stereoisomers of D-glucose or
D-fructose are formed i.e., alpha and beta structures.
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5. Mutorotation
• Anomers in monosaccharides are determined by the position of the –OH group
on the anomeric carbon, (e.g., α-D-glucose, -OH is below the ring and β-D-
glucose, -OH is above the ring).
• These two form ( α- and β- D- glucose may interconvert)
• Mutorotation is a process by which these two forms interconvert

6. Mutorotation
• When in solution, monosaccharides exist in equilibrium between the alpha and
beta anomer.
• Each form is in equilibrium with the open-chain form (the process by which it
goes back and forth is called mutorotation)
• Each time the chain closes, it can go to either form, although it turns out that
beta anomer more often (64% for glucose)

7. Reactions of monosaccharides

8. Glycoside formation synthesis
• Treatment of a monosaccharide with an alcohol and an acid catalyst yields a
hemi-acetal .
• Carbohydrate acetals are called glycosides. For example acetals of mannose are
called mannosides, of fructose > fructosides.
• The anomeric -OH has been replaced by an -OR group
– β-D-glucopyranose with methanol and acid gives a mixture of α and β methyl D-
glucopyranosides

9. Glycoside formation
• When acetals are exposed to acidic medium the glycoside undergo hydrolysis to
produce a sugar and an alcohol. The alcohol obtained is called a Aglycone.
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10. Koenigs-Knorr reaction
• Synthesis requires distinguishing the numerous -OH groups
• Treatment of monossacharide acetal with HBr converts anomeric -OH to Br.
• Addition of alcohol (with Ag2O) gives a β glycoside (Koenigs–Knorr reaction)

11. Ester formation
• OH groups can be converted into esters and ethers, which are often easier to
work with than the free sugars and are soluble in organic solvents.
• Esterification by treating with an acid chloride or acid anhydride in the presence
of a base converts all -OH groups including the anomeric OH to ester groups .

13. Ether formation
• Treatment with an alkyl halide in the presence of base—the Williamson ether
synthesis
• Use silver oxide as a catalyst with base-sensitive compounds

14. Chapter 23 14
Oxidation by bromine: aldonic acids
Bromine water oxidizes aldehyde to –CO2H, but not ketone or alcohol; forms
aldonic acid.
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15. Chapter 23 15
Oxidation by nitric acid; aldaric acid
Nitric acid oxidizes the aldehyde and the terminal alcohol as it is a stronger
oxidizing agent.
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16. Chapter 23 16
Oxidation by Tollen’s or Benedicts Reagent
• Tollen’s reagent reacts with aldehyde, but the base promotes enediol
rearrangements, so ketoses react too.
• Sugars that give a silver mirror with Tollen’s are called reducing sugars.

17. Oxidation by Benedicts reagent
Occurs in an alkaline solution.

18. Chapter 23 18
Non-reducing Sugars
• Carbohydrates that only contain acetal groups are stable in base, so they do not
react with Tollen’s or Benedicts reagent thus called non-reducing sugars.
• Disaccharides and polysaccharides are also acetals, non-reducing sugars.
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19. Chapter 23 19
Ruff Degradation: chain shortening
Aldose chain is shortened by oxidizing the aldehyde to -COOH, then
decarboxylation.
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20. Wohl Degradation: chain shortening
• Shortens aldose chain by one CH2OH

21. Chapter 23 21
Kiliani-Fischer Synthesis
• This process lengthens the aldose chain.
• A mixture of C-2 epimeric cynohydrins are formed and can be separated easily as
they are diasteriosomers.