Organic Chemistry
Organic Chemistry
8th Edition
ISBN: 9781305580350
Author: William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Publisher: Cengage Learning
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Question
Chapter 25, Problem 25.25P

(a)

Interpretation Introduction

Interpretation:

The product formed by the reaction of D-ribose with NaBH4 and H2O has to be drawn in Fischer projection and the product is optically active or inactive has to be stated.

Concept Introduction:

The reaction of NaBH4 and H2O with carbohydrates is a reduction reaction.  The carbonyl group in the carbohydrate is reduced to alcoholic group and forms alditols.

(a)

Expert Solution
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Explanation of Solution

The D-ribose is an aldopentose molecule.  The carbonyl group present in D-ribose is aldehyde (-CHO).  When the D-ribose molecule is reacted with NaBH4 and H2O, the aldehyde group is reduced to alcohol group (-CH2OH) forming the alditol product.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  1

The D-ribitol is a meso compound and shows plane of symmetry.  So, it is optically inactive.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  2

(b)

Interpretation Introduction

Interpretation:

The product formed by the reaction of D-ribose with H2/Pt has to be drawn in Fischer projection and the product is optically active or inactive has to be stated.

Concept Introduction:

The reagent H2/Pt is a reducing agent which reduces the carbonyl group into alcoholic group.  The carbonyl group in the carbohydrate is reduced to alcoholic group and forms alditols.

(b)

Expert Solution
Check Mark

Explanation of Solution

When the D-ribose molecule is made to react with H2/Pt, the aldehyde group is reduced to alcoholic group forming the alditol.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  3

The D-ribitol is a meso compound and shows plane of symmetry.  So, it is optically inactive.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  4

(c)

Interpretation Introduction

Interpretation:

The product formed by the reaction of D-ribose with warm HNO3 has to be drawn in Fischer projection and the product is optically active or inactive has to be stated.

Concept Introduction:

The reaction of warm HNO3 with carbohydrates is a oxidation reaction.  The carbonyl groups and alcoholic groups in the carbohydrate is oxidised to acid groups.

(c)

Expert Solution
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Explanation of Solution

The nitric acid (HNO3) is an oxidising agent.  It oxidises the alcoholic groups and carbonyl groups into acidic groups.  In D-ribose, the aldehyde group (C1) and the alcoholic group (C5) are oxidised to acid groups forming D-ribaric acid.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  5

The product formed is a meso compound and shows plane of symmetry.  So, it is optically inactive.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  6

(d)

Interpretation Introduction

Interpretation:

The product formed by the reaction of D-ribose with Br2/H2O/CaCO3 has to be drawn in Fischer projection and the product is optically active or inactive has to be stated.

Concept Introduction:

The reaction of Br2/H2O/CaCO3 with carbohydrates is a oxidation reaction.  The carbonyl group in the carbohydrate is oxidised to acid group.  It is a mild oxidising agent compared to HNO3.

(d)

Expert Solution
Check Mark

Explanation of Solution

When the D-ribose reacts with Br2/H2O/CaCO3, the aldehyde group is oxidised to acid group forming the acidic product, D-ribonic acid.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  7

The D-ribonic acid is a chiral molecule and is optically active.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  8

(e)

Interpretation Introduction

Interpretation:

The product formed by the reaction of D-ribose with H5IO6 has to be drawn in Fischer projection and the product is optically active or inactive has to be stated.

Concept Introduction:

The reaction of H5IO6 oxidises the carbohydrate molecule by cleaving the carbon-carbon bonds.  It forms many cleaved products of the carbohydrate.

(e)

Expert Solution
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Explanation of Solution

The D-ribose molecule consumes 4H5IO6 molecules to cleave the five carbon-carbon bonds.  The aldehyde group and hydroxyl groups (C2-C4) are reduced to acid groups and the C5 alcohol group is converted to aldehyde group.  It forms five products among which four are formic acid molecules and one is formaldehyde.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  9

The products formed are achiral and are optically inactive.

(f)

Interpretation Introduction

Interpretation:

The product formed by the reaction of D-ribose with aniline (C6H5NH2) has to be drawn in Fischer projection and the product is optically active or inactive has to be stated.

(f)

Expert Solution
Check Mark

Explanation of Solution

The D-galactose molecule reacts with aniline molecule and the aldehyde group of carbohydrate is reacted with the amine group of aniline.  By the loss of water molecule, it forms Schiff’s base of D-ribose.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  10

The product formed is chiral and optically active.

Organic Chemistry, Chapter 25, Problem 25.25P , additional homework tip  11

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Students have asked these similar questions
An unknown reducing disaccharide is found to be unaffected by invertase enzymes. Treatment with an a@galactosidasecleaves the disaccharide to give one molecule of d-fructose and one molecule of d-galactose. When the disaccharideis treated with excess iodomethane and silver oxide and then hydrolyzed in dilute acid, the products are2,3,4,6-tetra-O-methylgalactose and 1,3,4-tri-O-methylfructose. Propose a structure for this disaccharide, and give itscomplete systematic name.
Regarding the following monosaccharides, indicate the CORRECT alternative: a) Only Gulosa, Idosa and Mannose can produce alditols because they are aldoses. b) There is only one pair of epimers. c) The reaction of Idosa with HNO3 converts it into a product without optical activity. d) Only two monosaccharides will give a positive result with Fehling's reagent. e) Mutarotation converts D-psychose into an aldose.
A D-aldopentose A is reduced to an optically active alditol. Upon Kiliani–Fischer synthesis, A is converted to two Daldohexoses, B and C. B is oxidized to an optically inactive aldaric acid. C is oxidized to an optically active aldaric acid. What are the structures of A–C?
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