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Ch 21 Carbohydrates

Ch 21 Carbohydrates. 1. Draw Fischer projections of all the aldotetrose stereoisomers. Name and label D & L and indicate enantiomers. Ch 21 Carbohydrates. 2. One form of galactose is drawn below. Describe the sugar in all possible terms How many stereocenters does it have?

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Ch 21 Carbohydrates

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  1. Ch 21 Carbohydrates 1. Draw Fischer projections of all the aldotetrose stereoisomers. Name and label D & L and indicate enantiomers.

  2. Ch 21 Carbohydrates 2. One form of galactose is drawn below. • Describe the sugar in all possible terms • How many stereocenters does it have? • How many stereoisomers does it have? • Is this D or L form?

  3. Ch 21 Carbohydrates 3. Comparing these to galactose from last problem… a. Which is a ketose? b. Which is L-galactose? c. Which is a C-3 epimer of D-galactose?

  4. Ch 21 Carbohydrates 4. Complete the following reactions: a. b.

  5. Ch 21 Carbohydrates 5. Answer the following: a.Which aldohexoses will form an optically inactive aldaric acid? b. Which sugar, when reduced with NaBH4, will form D-glucitol and D-mannitol?

  6. Ch 21 Carbohydrates 6. Identify unknown sugars X, Y and Z from the following info: i) ii) iii)

  7. Ch 21 Carbohydrates …(#6 cont’d) X is one of the following:

  8. Ch 21 Carbohydrates 7. Draw the Haworth projections and chair conformers (if possible) for the following: • β–D-glucopyranose • α-L-mannopyranose • methyl β–D-galactopyranoside • α -D-ribofuranose 8. Which of these are reducing sugars?

  9. Ch 21 Carbohydrates 9. Give the major product for the following: a. c. b.

  10. Ch 21 Carbohydrates 10. An unknown disaccharide gives a positive Tollen’s test. A glycosidase hydrolyzes it to D-galactose and D-mannose. When the disaccharide is treated with methyl iodide and Ag2O and then hydrolyzed with dilute HCl, the products are 2,3,4,6-tetra-O-methylgalactose and 2,3,4-tri-O-methylmannose. Propose a structure for the dissacharide.

  11. Ch 21 Carbohydrates 11. What’s the primary structural difference between: • maltose and lactose • lactose and sucrose • amylose and amylopectin • amylose and cellulose

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