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Lecture8 carbohydrates



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  • 1. Carbohydrates Classification Monosaccharides Chiral Carbon Atoms Structures of Important Monosaccharides Cyclic Structures 1
  • 2. Carbohydrates • Major source of energy from our diet • Composed of the elements C, H and O • Produced by photosynthesis in plants 2
  • 3. Types of Carbohydrates • Monosacchrides • Disaccharides Contain 2 monosacchride units • Polysacchrides Contain many monosacchride units 3
  • 4. Monosacchrides • Three Carbons = Triose • Four Carbons = Tetrose • Five Carbons = Pentose • Six Carbons = Hexose 4
  • 5. Monosacchrides • Aldoses are monosacchrides with an aldehyde group and many hydroxyl (-OH) groups. • Ketoses are monosacchrides with a ketone group and many hydroxyl (-OH) groups. 5
  • 6. Learning Check C1 Identify each as tetrose, pentose or hexose, and as aldose or ketose H C O CH2OH H C OH C O H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH A B 6
  • 7. Solution C1 H C O CH2OH H C OH C O H C OH H C OH HO C H H C OH H C OH CH2OH CH2OH A B aldose, hexose ketose, pentose 7
  • 8. Chiral Objects • Chiral compounds have the same number of atoms arranged differently in space. • A chiral carbon atom has four different groups attached 8
  • 9. Mirror Images • The three-dimensional structure of a chiral compound has a mirror image. • Your hands are chiral. Try to superimpose your thumbs, palms, back of hands, and little fingers. Is it possible? Why or why not? 9
  • 10. Tetrahedral carbon atom bonded to four different groups 10
  • 12. Learning Check C2 Determine if there is a chiral carbon in each compound. Cl Cl H C CH 3 H C CH3 CH 2 CH 3 H A B 12
  • 13. Solution C2 Cl Cl H C CH3 H C CH3 CH2CH3 H A Yes, 4 different B No, the groups are attached 2 H atoms to the second C atom are identical 13
  • 14. 14
  • 15. Glyceraldehyde 15
  • 16. D and L Notation • D,L tells which of the two chiral isomers we are referring to. • If the –OH group on the next to the bottom carbon atom points to the right , the isomer is a D-isomer; if it points left, the isomer is L. • The D form is usually the isomer found in nature. 16
  • 17. D notation O H C H C OH H C OH CH2OH Right = D 17
  • 18. Glucose H C O H C OH HO C H H C OH H C OH CH2OH D-Glucose 18
  • 19. Fructose CH2 OH C O HO C H H C OH H C OH CH2OH D-Fructose 19
  • 20. Galactose H O C H C OH HO C H HO C H H C OH CH2OH D-galactose 20
  • 21. Cyclic Structures • Monosaccharides with 5-6 carbon atoms form cyclic structures • The hydroxyl group on C-5 reacts with the aldehyde group or ketone group O o 21
  • 22. Haworth Structure for D-Isomers The cyclic structure of a D-isomer has the final CH2OH group located above the ring. CH2OH o 22
  • 23. Haworth Structure for D- Glucose • Write –OH groups on the right (C2, C4) up • Write –OH groups on the left (C3) down • The new –OH on C1 has two possibilites: down for α anomer, up for β anomer 23
  • 24. Cyclization of glucose 24
  • 25. Haworth Structure for D- Glucose CH2OH CH2OH o o OH β OH OH OH OH OH α OH OH α-D-Glucose β-D-Glucose 25
  • 26. d-fructose 26
  • 27. Mutarotation • Mutarotation: A small amount of open chain is in equilibrium with the cyclic forms. • The most stable form of glucose is β-D- glucose . α-D-glucose D-glucose (open) β-D-glucose (36%) (trace) (64%) 27
  • 28. Learning Check C3 Write the cyclic form of α-D-galactose H O C H C OH HO C H HO C H H C OH CH2OH 28
  • 29. Solution C3 CH2OH OH o OH OH OH α-D-galactose 29