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Chapter 25 Carbohydrates

Chapter 25 Carbohydrates. 25.1 Classification of Carbohydrates. Classification of Carbohydrates. monosaccharide disaccharide oligosaccharide polysaccharide. Monosaccharide. is not cleaved to a simpler carbohydrate on hydrolysis glucose, for example, is a monosaccharide.

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Chapter 25 Carbohydrates

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  1. Chapter 25Carbohydrates

  2. 25.1Classification of Carbohydrates

  3. Classification of Carbohydrates • monosaccharide • disaccharide • oligosaccharide • polysaccharide

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

  5. C6H12O6 + C6H12O6 glucose(a monosaccharide) fructose(a monosaccharide) Disaccharide • is cleaved to two monosaccharides on hydrolysis • these two monosaccharides may be the same or different C12H22O11 + H2O sucrose(a disaccharide)

  6. Higher Saccharides • oligosaccharide: • gives two or more monosaccharide units on hydrolysis is homogeneous—all molecules of a particular oligosaccharide are the same, including chain length • polysaccharide: • yields "many" monosaccharide units on hydrolysis mixtures of the same polysaccharide differing only in chain length

  7. Table 25.1 Some Classes of Carbohydrates • No. of carbons AldoseKetose • 4 AldotetroseKetotetrose • 5 AldopentoseKetopentose • 6 AldohexoseKetopentose • 7 AldoheptoseKetoheptose • 8 AldooctoseKetooctose

  8. 25.2Fischer Projections and D-L Notation

  9. Fischer Projections

  10. Fischer Projections

  11. Fischer Projections of Enantiomers

  12. CH O CH O H OH HO H D L CH2OH CH2OH Enantiomers of Glyceraldehyde (+)-Glyceraldehyde (–)-Glyceraldehyde

  13. 25.3The Aldotetroses

  14. CH O H OH H OH D CH2OH An Aldotetrose 1 • stereochemistry assigned on basis of whetherconfiguration of highest-numbered stereogenic centeris analogous to D or L-glyceraldehyde 2 3 4

  15. CH O H OH H OH CH2OH An Aldotetrose 1 2 3 4 D-Erythrose

  16. CH O CH O H OH HO H H OH HO H CH2OH CH2OH The Four Aldotetroses • D-Erythrose and L-erythrose are enantiomers D-Erythrose L-Erythrose

  17. CH O CH O H OH H HO H OH H OH CH2OH CH2OH The Four Aldotetroses • D-Erythrose and D-threose are diastereomers D-Erythrose D-Threose

  18. CH O CH O HO H H HO HO H H OH CH2OH CH2OH The Four Aldotetroses • L-Erythrose and D-threose are diastereomers L-Erythrose D-Threose

  19. CH O CH O H OH H HO H HO H OH CH2OH CH2OH The Four Aldotetroses • D-Threose and L-threose are enantiomers L-Threose D-Threose

  20. CH O CH O CH O CH O H OH HO H OH H HO H H OH H OH HO HO H CH2OH CH2OH CH2OH CH2OH The Four Aldotetroses H D-Erythrose L-Erythrose D-Threose L-Threose

  21. 25.4Aldopentoses and Aldohexoses

  22. 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.

  23. CH O CH O CH O CH O OH HO H OH HO H H H OH OH HO H H HO H H OH OH OH OH H H H H CH2OH CH2OH CH2OH CH2OH The Four D-Aldopentoses D-Ribose D-Arabinose D-Xylose D-Lyxose

  24. 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.

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