The two possible structures for the β -D-aldohexose are to be distinguished. Concept Introduction: The Wohl-degradation is opposite of the Killiani-Fisher synthesis. It shortens an aldoses chain by one carbon. Hexoses are converted to pentoses and pentoses are converted to tetroses. Aldehyde group reacts with hydroxylamine to form an oxime. It is heated with acetic anhydride to dehydrate the oxime forming a cyano group and all the hydroxyl groups are converted to esters. All the ester groups are hydrolyzed in a basic aqueous solution and the cyano group is eliminated.

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Definition Definition Organic compounds that have a carbonyl group, C=O, as their functional group. The carbonyl group in aldehydes is placed at the end of the molecular structure, which means the C=O is attached to one hydrogen atom and an alkyl group or a benzene ring. Just like all the other homologous series in organic chemistry, the naming of aldehydes uses the suffix “-al”. The general molecular formula is C n H 2n O.

Chapter 20, Problem 48P

Interpretation Introduction

Interpretation:

The two possible structures for the β-D-aldohexose are to be distinguished.

Concept Introduction:

The Wohl-degradation is opposite of the Killiani-Fisher synthesis. It shortens an aldoses chain by one carbon. Hexoses are converted to pentoses and pentoses are converted to tetroses. Aldehyde group reacts with hydroxylamine to form an oxime. It is heated with acetic anhydride to dehydrate the oxime forming a cyano group and all the hydroxyl groups are converted to esters. All the ester groups are hydrolyzed in a basic aqueous solution and the cyano group is eliminated.

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An unknown β-d-aldohexose has only one axial substituent. A Wohl degradation forms a compound which, when treated with sodium borohydride, forms an optically active alditol. This information allows you to arrive at two possible structures for the β-d-aldohexose. What experiment can you carry out to distinguish between the two possibilities?

When an optically active D-aldopentose was subjected to Kiliani-Fischer synthesis, followed by NaBH4/H2O, it produced a mixture of an optically active and an optically inactive alditol. When the same D-aldopentose was subjected to Wohl degradation followed by HNO3 it produced an optically inactive aldaric acid. Provide the structure of this D-aldopentose. Н- НО- н- H -ОН НО -H Н- -Н CH₂OH 1 A) 1 B) II C) III осн H D) IV НО осн -H Н- -OH H- H HỌ CH₂OH П -OH H -OH H Н -H CH₂OH Ш _H -OH HO -OH H- -OH H- осн -H -OH CH₂OH IV -OH CH₂OH V

An important technique for establishing relative configurations among isomeric aldoses and ketoses is to convert both terminal carbon atoms to the same functional group. This can be done either by selective oxidation or reduction. As a specific example, nitric acid oxidation of d-erythrose gives meso-tartaric acid . Similar oxidation of d-threose gives (2S,3S)-tartaric acid. Given this information and the fact that d-erythrose and d-threose are diastereomers, draw Fischer projections for d-erythrose and d-threose. Check your answers against Table 25.1.

Answer 2

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Definition Definition Organic compounds that have a carbonyl group, C=O, as their functional group. The carbonyl group in aldehydes is placed at the end of the molecular structure, which means the C=O is attached to one hydrogen atom and an alkyl group or a benzene ring. Just like all the other homologous series in organic chemistry, the naming of aldehydes uses the suffix “-al”. The general molecular formula is C n H 2n O.

Chapter 20, Problem 48P

Interpretation Introduction

Interpretation:

The two possible structures for the β-D-aldohexose are to be distinguished.

Concept Introduction:

The Wohl-degradation is opposite of the Killiani-Fisher synthesis. It shortens an aldoses chain by one carbon. Hexoses are converted to pentoses and pentoses are converted to tetroses. Aldehyde group reacts with hydroxylamine to form an oxime. It is heated with acetic anhydride to dehydrate the oxime forming a cyano group and all the hydroxyl groups are converted to esters. All the ester groups are hydrolyzed in a basic aqueous solution and the cyano group is eliminated.

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Answer 3

Question

Definition Definition Organic compounds that have a carbonyl group, C=O, as their functional group. The carbonyl group in aldehydes is placed at the end of the molecular structure, which means the C=O is attached to one hydrogen atom and an alkyl group or a benzene ring. Just like all the other homologous series in organic chemistry, the naming of aldehydes uses the suffix “-al”. The general molecular formula is C n H 2n O.

Chapter 20, Problem 48P

Interpretation Introduction

Interpretation:

The two possible structures for the β-D-aldohexose are to be distinguished.

Concept Introduction:

The Wohl-degradation is opposite of the Killiani-Fisher synthesis. It shortens an aldoses chain by one carbon. Hexoses are converted to pentoses and pentoses are converted to tetroses. Aldehyde group reacts with hydroxylamine to form an oxime. It is heated with acetic anhydride to dehydrate the oxime forming a cyano group and all the hydroxyl groups are converted to esters. All the ester groups are hydrolyzed in a basic aqueous solution and the cyano group is eliminated.

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Check out a sample textbook solution

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Answer 4

Question

Definition Definition Organic compounds that have a carbonyl group, C=O, as their functional group. The carbonyl group in aldehydes is placed at the end of the molecular structure, which means the C=O is attached to one hydrogen atom and an alkyl group or a benzene ring. Just like all the other homologous series in organic chemistry, the naming of aldehydes uses the suffix “-al”. The general molecular formula is C n H 2n O.

Chapter 20, Problem 48P

Interpretation Introduction