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Chapter 23: Q24P (page 1226)

Treatment of either anomer of fructose with excess ethanol in the presence of a trace of HCI gives a mixture of the α and β anomers of ethyl-D-fructofuranoside. Draw the starting materials, reagents, and products for this reaction. Circle the aglycone in each product.

Short Answer

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An anomer is an epimer of a cyclic sugar which possess different configuration at the anomeric carbon. An epimer is one of a pair of stereoisomers which differs only at one stereocenter. For each set of anomers, there exists an alpha anomer and a beta anomer. Anomeric carbon is the hemiacetal or hemiketal carbon of that particular sugar. Fructose hasand-D-fructofuranose as anomers.

Step by step solution

01

Step-1.

An anomer is an epimer of a cyclic sugar which possess different configuration at the anomeric carbon. An epimer is one of a pair of stereoisomers which differs only at one stereocenter. For each set of anomers, there exists an alpha anomer and a beta anomer. Anomeric carbon is the hemiacetal or hemiketal carbon of that particular sugar. Fructose hasand-D-fructofuranose as anomers.

02

Step-2.

Treatment of either anomer of fructose with excess ethanol and trace of hydrochloric acid gives a mixture of and anomers of ethyl-D-fructofuranoside. Aglycone is the non-sugar part of the glycoside. Aglycone part is circled in both the products.

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Most popular questions from this chapter

Does lactose mutarotate? Is it a reducing sugar? Explain. Draw the two anomeric forms of lactose.

In 1891, Emil Fischer determined the structures of glucose and seven other D-aldohexoses using only simple chemical reactions and clever reasoning about stereochemistry and symmetry. He received the Nobel Prize for this work in 1902. Fischer has determined that D-glucose is an aldohexose, and he used Ruff degradation to degrade it to (+)-glyceraldehyde. Therefore, the eight D-aldohexose structures shown in Figure 23-3 are the possible structures for glucose.

Pretend that no names are shown in Figure 23-3 except for glyceraldehyde, and sue the following results to prove which of these structures represent glucose, mannose, arabinose, and erythrose.

(a)Upon Ruff degradation, glucose and mannose gives the same aldopentose: arabinose.Nitric acid oxidation of arabinose gives an optically active aldaric acid. What are the two possible structures of arabinose?

(b) Upon Ruff degradation, arabinose gives the aldotetrose erythrose. Nitric acid oxidation of erythrose gives an optically inactive aldaric acid, meso-tartaric acid. What is the structure of erythrose?

(c) Which of the two possible structures of arabinose is correct? What are the possible structures of glucose and mannose?

(d) Fischer’s genius was needed to distinguish between glucose and mannose. He developed a series of reactions to convert the aldehyde group of an aldose to an alcohol while converting the terminal alcohol to an aldehyde. In effect, he swapped the functional groups on the ends. When he interchanged the functional groups on D-mannose, he was astonished to find that the product was still D-mannose. Show how this information completes the proof of the mannose structure, and show how it implies the correct glucose structure.

(e) When Fischer interchanged the functional groups on D-glucose, the product was an unnatural L sugar. Show which unnatural sugar he must have formed, and show how it completes the proof of the glucose structure.

Question: Exposure to nitrous acid (see Section 19-16), sometimes found in cells, can convert cytosine to uracil.

  1. Propose a mechanism for this conversion.
  2. Explain how this conversion would be mutagenic upon replication.
  3. DNA generally includes thymine, rather than uracil(found in RNA). Based on this fact, explain why the nitrous acid-induced mutation of cytosine to uracil is more easily repaired in DNA than it is in RNA.

Cellulose is converted to cellulose acetateby treatment with acetic anhydride and pyridine. Cellulose acetate is soluble in common organic solvents, and it is easily dissolved and spun into fibers. Show the structure of cellulose acetate.

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

(a) methylα‐D‐galactopyranoside (b) β‐L‐idopyranose (an aldohexose)

(c) α‐D‐allopyranose (d) β‐L‐ribofuranoside

(e) (f)
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