28. Carbohydrates

Draw the structures of the compound methyl α-D-galactopyranoside.

Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.

Provide the mechanism for the cyclic hemiacetal formation of the following hydroxycarbonyl.

4-Hydroxy- and 5-hydroxyaldehydes exist primarily as cyclic hemiacetals. Draw the structure of the cyclic hemiacetal formed by each of the following:

b. 4-hydroxypentanal

When monosaccharides form cyclic hemiacetals, which type of molecule is released during the linkage process?

What type of bonds are formed when monosaccharides form cyclic hemiacetals?

In the formation of a cyclic hemiacetal from a monosaccharide, what type of reaction occurs?

Where does the chemical digestion of table sugar ($\mathrm{sucrose}$) begin in the human body?

Monosaccharides may link together to form polysaccharides by forming which type of bond?

Without referring to the chapter, draw the chair conformations of

(d) N-acetylglucosamine, glucose with the C2 oxygen atom replaced by an acetylated amino group.

The carbonyl group in D-galactose may be isomerized from C1 to C2 by brief treatment with dilute base (by the enediol rearrangement). The product is the C4 epimer of fructose. Draw the furanose structure of the product.

Draw the mechanism for the interconversion of α-D-glucose and β-D-glucose in dilute HCl.

Draw the structures of the compound ethyl β-D-ribofuranoside.

Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.

Without referring to the chapter, draw the chair conformations of

(b) α-D-allopyranose (the C3 epimer of glucose).

Two structures for the sugar glucose are shown on page 914. Interconversion of the open-chain and cyclic hemiacetal forms is catalyzed by either acid or base.

(b) The cyclic hemiacetal is more stable than the open-chain form, so very little of the open-chain form is present at equilibrium. Will an aqueous solution of glucose reduce Tollens reagent and give a positive Tollens test? Explain.

Draw the structures of the compound α-D-allopyranose.

Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.