1. Draw the structure of D-erythrose as (1) a Fischer Projection
(2) a wedge-and-dash structure and (3) a Newman projection. What
kind of conformation does this represent? How many stereocenters
does D-erythrose have? How many stereoisomers are there? How many
diastereoisomers? Draw the Fischer structures of the other stereoisomers
of D-erythrose. Which one is L-erythrose? Why is erythrose termed
2. Draw the Fischer structures of all of the diastereoisomeric
D- aldopentoses. Which one is D-ribose? Which one is D-arabinose?
3. Draw the Fischer structures of D-glucose, D-mannose, and D-fructose.
Number the carbon atoms of each. Explain and sketch mechanistically
how D-glucose can be converted to D-mannose? Can D-glucose be
readily converted to L-glucose? If so, how? Show how D-glucose
and D-mannose can be converted, in part, to D-fructose.
4. Draw the conformational structures of D-glucopyranose and D-mannopyranose.
Which one is more thermodynamically stable? Why? Of the two anomers
of D-glucopyranose, which is imore stable, the alpha or beta?
Why? What principle is involved? Explain, on thermodynamic grounds,
why the cyclic hemiacetal form is favored over the acyclic form.
In forming the cyclic hemiacetal form, which hydroxyl group of
the acyclic form must add to the carbonyl group in order to give
the six-membered ring?
5. Explain why, when pure b-D-glucopyranose
is dissolved in water, the specific rotation gradually changes
and then becomes steady. Explain why this steady state specific
rotation is the same whether we start with the alpha or beta anomer.
What is this phenomenon called? Sketch the mechanism for the interconversion
of the alpha and beta anomers. What key intermediate is involved?
6. Write a mechanism for the conversion of b-D-glucopyranose
to the corresponding methyl glycoside, by reaction with methanol
in water. What kind of linkage is present in a glycoside?
7. Why is b-D-glucopyranose also called
"dextrose". Does the "D" in b-D-glucopyranose
imply that its rotation is positive? Why or why not?
8. Draw the structure of D-ribofuranose. Why is is termed "furanose"
and not "pyranose"? Which hydroxyl group of the acyclic
form of D-ribose must add to the aldehyde function to form the
furanose ring. Which one would have to add to form an aldopyranose
structure? Which form occurs in RNA? Is this because the aldopyranose
structure is too unstable? Under what conditions can D-ribopyranose
9. Draw the structures of maltose and cellobiose and identify
both the acetal and the hemiacetal linkages of each. Which linkage
makes these disaccharides "reducing sugars"? Why? Why
are these called "disaccharides"? Which alcohol function
of D-glucopyranose reacts to form the acetal function on the other
D-glucopyranose? Is there more than one isomer of maltose, e.g.?
Explain and draw the structures of any isomers which are still
10. Draw the repeat structures of cellulose and starch (amylose)
and point out the structural differences and any differences in
11. Look at the structure of sucrose in your book. What two simple
sugars are combined to generate this disaccharide? Is this sugar
a "reducing sugar"? Why or why not? Point out any functional
groups in this disaccharide other than simple alcohol functions.
12. Draw the structure of D-deoxyribose. Where is it found in nature. To which carbon are the bases bound? The phosphate moieties?