20. Carbohydrates

Identify each pair of carbohydrates as enantiomers or diastereomers.

Draw the enantiomer of given structure of Xylose, and identify as D or L.

Aldoheptoses have five chiral carbon atoms. What is the maximum possible number of aldoheptose stereoisomers? Draw all of the aldoheptose stereoisomers.

Only three stereoisomers are possible for 2,3-dibromo-2, 3-dichlorobutane. Draw them, indicating which pair are enantiomers (optical isomers). Why does the other isomer not have an enantiomer?

Sucrose and D-glucose rotate plane-polarized light to the right; D-fructose rotates light to the left. When sucrose is hydrolyzed, the glucose–fructose mixture rotates light to the left.

b. Why do you think the mixture is called “invert sugar”?

 Identify each of the following pairs of Fischer projections as enantiomers or identical compounds:

a.

 Identify each of the following pairs of Fischer projections as enantiomers or identical compounds:

a.

 Identify each of the following pairs of Fischer projections as enantiomers or identical compounds:

c.

Indicate whether each pair of Fischer projections represents enantiomers or identical structures.

a.

Indicate whether each pair of Fischer projections represents enantiomers or identical structures.

b.

Draw the Fischer projection of the C3 epimer of D-glucose. Compare your structure with those in Table 6.1 and give the name of this compound.

Draw the Fischer projection for the enantiomer (mirror image) of each of the following:

(a)

Classify structures A, B, and C in the figure as being either an enantiomer or a diastereomer of D-galactose.

Use the structure of D-galactose in Problem 6.15 to answer the following:

(a) Draw the Fischer projection of the carbon 3 epimer.