Ch. 23 - Carbohydrates and Nucleic Acids

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 23 - Carbohydrates and Nucleic Acids

Problem 59e

Chapter 23, Problem 59e

Show what product results if the aldopentose formed from degradation of X is further degraded to an aldotetrose. Does HNO₃ oxidize this aldotetrose to an optically active aldaric acid?

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Identify the aldopentose formed from the degradation of compound X. Aldopentoses are monosaccharides with five carbon atoms, including an aldehyde group. The degradation process typically involves the removal of one carbon atom from the original sugar, often through the Ruff degradation method.

Perform a second degradation step to convert the aldopentose into an aldotetrose. Aldotetroses are monosaccharides with four carbon atoms, including an aldehyde group. This step involves the removal of another carbon atom, again typically through a Ruff degradation or similar process.

Draw the structure of the resulting aldotetrose. Ensure that the stereochemistry of the molecule is preserved during the degradation process. The stereochemistry of the aldotetrose will depend on the configuration of the original aldopentose.

Determine whether the aldotetrose can be oxidized by HNO₃ (nitric acid) to form an aldaric acid. HNO₃ oxidizes both the aldehyde group and the terminal primary alcohol group of the sugar to carboxylic acids. Check if the resulting aldaric acid is optically active by analyzing its symmetry. If the molecule has a plane of symmetry, it will be optically inactive.

Conclude whether the aldaric acid formed from the oxidation of the aldotetrose is optically active or inactive. This depends on the stereochemistry of the aldotetrose and whether the oxidation product has a chiral center or a plane of symmetry.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Aldopentose and Aldotetrose

Aldopentoses are monosaccharides with five carbon atoms and an aldehyde group, while aldotetroses have four carbon atoms and also contain an aldehyde group. The degradation of aldopentoses can yield aldotetroses through the loss of a carbon atom. Understanding the structural differences and the process of degradation is essential for predicting the products formed in carbohydrate chemistry.

Oxidation Reactions in Organic Chemistry

Oxidation reactions involve the loss of electrons or an increase in oxidation state, often resulting in the formation of carboxylic acids from aldehydes. In this context, HNO3 (nitric acid) can oxidize the aldotetrose to an aldaric acid, which contains two carboxylic acid groups. Recognizing the role of oxidizing agents is crucial for understanding how carbohydrates can be transformed into different functional groups.

Optical Activity and Aldaric Acids

Optical activity refers to the ability of a compound to rotate plane-polarized light, which is a characteristic of chiral molecules. Aldaric acids, derived from aldoses, can be optically active if they possess chiral centers. Determining whether the resulting aldaric acid from the oxidation of the aldotetrose is optically active involves analyzing its structure and the presence of chiral centers.

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Mutorotation and Optical Activity

Related Practice

Textbook Question

Sugar X is known to be a D-aldohexose. On oxidation with HNO₃, X gives an optically inactive aldaric acid. When X is degraded to an aldopentose, oxidation of the aldopentose gives an optically active aldaric acid. Determine the structure of X.

Textbook Question

Some protecting groups can block two OH groups of a carbohydrate at the same time. One such group is shown here, protecting the 4-OH and 6-OH groups of β-d-glucose.

(a) What type of functional group is involved in this blocking group?

(b) What did glucose react with to form this protected compound?

(c) When this blocking group is added to glucose, a new chiral center is formed. Where is it? Draw the stereoisomer that has the other configuration at this chiral center. What is the relationship between these two stereoisomers of the protected compound?

(d) Which of the two stereoisomers in part (c) do you expect to be the major product? Why?

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Textbook Question

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.

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Textbook Question

An important protecting group developed specifically for polyhydroxy compounds like nucleosides is the tetraisopropyldisiloxanyl group, abbreviated TIPDS, that can protect two alcohol groups in a molecule.

(a) The TIPDS group is somewhat hindered around the Si atoms by the isopropyl groups. Which OH is more likely to react first with TIPDS chloride? Show the product with the TIPDS group on one oxygen.

(b) Once the TIPDS group is attached at the first oxygen, it reaches around to the next closest oxygen. Show the final product with two oxygens protected.

(c) The unprotected hydroxy group can now undergo reactions without affecting the protected oxygens. Show the product after the protected nucleoside from (b) is treated with tosyl chloride and pyridine, followed by NaBr, ending with deprotection with Bu₄NF.

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Textbook Question

Which of the D-aldotetroses will give optically active aldaric acids on oxidation with HNO₃?

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Textbook Question

Even though sugar X gives an optically inactive aldaric acid, the pentose formed by degradation gives an optically active aldaric acid. Does this finding contradict the principle that optically inactive reagents cannot form optically active products?

Show what product results if the aldopentose formed from degradation of X is further degraded to an aldotetrose. Does HNO3 oxidize this aldotetrose to an optically active aldaric acid?

Verified video answer for a similar problem:

Key Concepts

Aldopentose and Aldotetrose

Oxidation Reactions in Organic Chemistry

Optical Activity and Aldaric Acids

Show what product results if the aldopentose formed from degradation of X is further degraded to an aldotetrose. Does HNO₃ oxidize this aldotetrose to an optically active aldaric acid?