ch 21 carbohydrates

Ch 21 Carbohydrates1. Draw Fischer projections of all the aldotetrose stereoisomers. Name and label D & L and indicate enantiomers.

Ch 21 Carbohydrates2. One form of galactose is drawn below.

a.Describe the sugar in all possible terms

b.How many stereocenters does it have?

c.How many stereoisomers does it have?

d.Is this D or L form?

Ch 21 Carbohydrates3. 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?

Ch 21 Carbohydrates4. Complete the following reactions:

a. b.

OH

O

H OH

OH H

H OH

H OH

O H -

OH

O

H OH

OH H

H OH

H OH

1 . N a B H 4

2 . H 3O +

B r2 , H 3O +

o r A g , N H 3 , O H -

HNO3

Ch 21 Carbohydrates5. 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?

Ch 21 Carbohydrates6. Identify unknown sugars X, Y and Z from the following info:

i)

ii)

iii)

XW o h l d e g ra d a t io n

Yaldose aldotetrose

Y r e d u c t io n Zachiral alditol

L-glyderaldehydeK ilia n i -F is c h e r s y n th .

Y + diasteromer

Ch 21 Carbohydrates …(#6 cont’d)

X is one of the following:

Ch 21 Carbohydrates7. Draw the Haworth projections and chair conformers (if possible) for the following:

a.β–D-glucopyranose

b.α-L-mannopyranose

c.methyl β–D-galactopyranoside

d.α -D-ribofuranose

8. Which of these are reducing sugars?

Ch 21 Carbohydrates9. Give the major product for the following:

a. c.

b.

O

H

HH

H

OH

OH

H OH

OH

OH

C H 3I (x s )

A g 2O

O

H

HH

H

OH

OH

H OH

OH

OH

O

OO

(x s )

p y rid in e

O

H

HH

H

OH

OH

H OH

OH

OH

C H 3C H 2O H

H +

Ch 21 Carbohydrates10. 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.

Ch 21 Carbohydrates11. What’s the primary structural difference between:

a.maltose and lactose

b.lactose and sucrose

c.amylose and amylopectin

d.amylose and cellulose