Chapter 25 Carbohydrates

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Chapter 25Carbohydrates
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25.1Classification of Carbohydrates
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Classification of Carbohydrates

• monosaccharide
• disaccharide
• oligosaccharide
• polysaccharide

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Monosaccharide

• is not cleaved to a simpler carbohydrate on
  hydrolysis
• glucose, for example, is a monosaccharide

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Disaccharide

• is cleaved to two monosaccharides on hydrolysis
• these two monosaccharides may be the same or
  different

C12H22O11 H2O
sucrose(a disaccharide)
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Disaccharide

• is cleaved to two monosaccharides on hydrolysis
• these two monosaccharides may be the same or
  different

C12H22O11 H2O
C6H12O6 C6H12O6
glucose(a monosaccharide)
sucrose(a disaccharide)
fructose(a monosaccharide)
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Higher Saccharides

• oligosaccharide
• gives three or more monosaccharide units on
  hydrolysis
• polysaccharide
• yields more than 10 monosaccharide units

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Table 25.1 Some Classes of Carbohydrates

• No. of carbons Aldose Ketose
• 4 Aldotetrose Ketotetrose
• 5 Aldopentose Ketopentose
• 6 Aldohexose Ketopentose
• 7 Aldoheptose Ketoheptose
• 8 Aldooctose Ketooctose

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25.2Fischer Projections and D-L Notation
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Fischer Projections
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Fischer Projections
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Fischer Projections of Enantiomers
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Fischer Projections of Enantiomers
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Enantiomers of Glyceraldehyde
()-Glyceraldehyde
()-Glyceraldehyde
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25.3The Aldotetroses
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An Aldotetrose
1
2
3
4

• stereochemistry assigned on basis of
  whetherconfiguration of highest-numbered
  stereogenic centeris analogous to D or
  L-glyceraldehyde

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An Aldotetrose
1
2
3
D
4

• stereochemistry assigned on basis of
  whetherconfiguration of highest-numbered
  stereogenic centeris analogous to D or
  L-glyceraldehyde

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An Aldotetrose
1
2
3
4
D-Erythrose
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The Four Aldotetroses

• D-Erythrose and L-erythrose are enantiomers

D-Erythrose
L-Erythrose
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The Four Aldotetroses

• D-Erythrose and D-threose are diastereomers

D-Erythrose
D-Threose
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The Four Aldotetroses

• L-Erythrose and D-threose are diastereomers

L-Erythrose
D-Threose
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The Four Aldotetroses

• D-Threose and L-threose are enantiomers

L-Threose
D-Threose
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The Four Aldotetroses
H
D-Erythrose
L-Erythrose
D-Threose
L-Threose
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25.4Aldopentoses and Aldohexoses
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The Aldopentoses

• There are 8 aldopentoses.
• Four belong to the D-series four belong to the
  L-series.
• Their names are ribose, arabinose, xylose, and
  lyxose.

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The Four D-Aldopentoses
H
D-Ribose
D-Arabinose
D-Xylose
D-Lyxose
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The Four D-Aldopentoses
H
D-Ribose
D-Arabinose
D-Xylose
D-Lyxose
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The Four D-Aldopentoses
D-Ribose
D-Arabinose
D-Xylose
D-Lyxose
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The Four D-Aldopentoses
D-Ribose
D-Arabinose
D-Xylose
D-Lyxose
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Aldohexoses

• There are 16 aldopentoses.
• 8 belong to the D-series 8 belong to the
  L-series.
• Their names and configurations are best
  remembered with the aid of the mnemonic described
  in Section 25.5.