28. Carbohydrates

How many stereoisomers are possible for a $2-\mathrm{ketohexose}$, considering $D$ and $L$ isomerism?

Provide the generic name, including stereochemistry, for the following monosaccharide:

c. Draw d-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.

d. Draw the C4 “epimer” of D-xylose. Notice that this “epimer” is actually an L-series sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.

Indicate whether each of the following structures is D-glyceraldehyde or L-glyceraldehyde, assuming that the horizontal bonds point toward you and the vertical bonds point away from you (Section 4.7):

a.

b.

c.

Categorize the following monosaccharides as d or l.

(a)

Starting with a Fischer projection of d-glucose (and other sugars), switch only the stereocenter that gave it the designation of d. What new sugar have you made? [Hint: The answer is not l-glucose.]

Is the compound d or l?