28. Carbohydrates

Identify the following sugar as reducing sugars (RS) or non-reducing sugars (NS)

Identify the following sugar as reducing sugar(RS) or non-reducing sugar(NS)

Identify the following sugar as reducing sugar(RS) or non-reducing sugar(NS)

Identify the following sugar as reducing sugar(RS) or non-reducing sugar(NS)

Name the following compounds and indicate whether or not each is a reducing sugar:

a.

Is gentiobiose a reducing sugar? Does it mutarotate? Explain your reasoning

Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?

(a) methyl β-D-glucopyranoside

(b) 2,3,4,6-tetra-O-methyl-D-mannopyranose

(c) 1,3,6-tri-O-methyl-D-fructofuranose

(d) methyl 2,3,4,6-tetra-O-methyl-β-D-galactopyranoside

Which of the following are reducing sugars? Comment on the common name sucrose for table sugar.

(c) α-D-allopyranose

(d) ethyl β-D-ribofuranoside

Which of the following are reducing sugars? Comment on the common name sucrose for table sugar.

(e)

(f)

Name the following compounds and indicate whether or not each is a reducing sugar:

b.

Name the following compounds and indicate whether or not each is a reducing sugar:

c.

A hexose is obtained when the residue of a shrub Sterculia setigeria undergoes acid-catalyzed hydrolysis. Identify the hexose from the following experimental information: it undergoes mutarotation; it does not react with Br₂; and D-galactonic acid and D-talonic acid are formed when it reacts with Tollens’ reagent.

When the gum of the shrub Sterculia setigera is subjected to acidic hydrolysis, one of the water-soluble components of the hydrolysate is found to be tagatose. The following information is known about tagatose:

(1) Molecular formula C₆H₁₂O₆

(2) Undergoes mutarotation.

(3) Does not react with bromine water.

(4) Reduces Tollens reagent to give D-galactonic acid and D-talonic acid.

(5) Methylation of tagatose (using excess CH₃I and Ag₂O) followed by acidic hydrolysis gives 1,3,4,5-tetra-O-methyltagatose.

(a) Draw a Fischer projection structure for the open-chain form of tagatose.

Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?

(a) 4-O-(α-D-glucopyranosyl)-D-galactopyranose

Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?

(b) α-D-fructofuranosyl-β-D-mannopyranoside