Question 1

The Ruff degradation of two aldopentoses gives D-threose. Deduce the structures of the two aldopentoses.

Accepted Answer

The Ruff degradation will remove the top carbon of an aldopentose. Carbon 2 of the aldopentose will become the aldehyde carbon in the threose. Working backward, this means the aldopentoses must have been D-lyxose or D-xylose.

Question 2

A D-aldopentose forms two aldohexoses, A and B, after a Kiliani-Fisher synthesis. Aldohexose A is oxidized to an optically inactive aldaric acid, while aldohexose B is oxidized to an optically active aldaric acid. The aldopentose can also be oxidized to an optically inactive aldaric acid. Deduce the structures of the aldopentose and the two aldohexoses.

Accepted Answer

The Kiliani-Fischer synthesis adds a carbon to an aldopentose to generate the two aldohexoses. The aldopentose and aldohexoses can be oxidized to aldaric acids, where the top and bottom carbons of the Fischer projections are both carboxylic acids. The aldopentose gives an optically inactive aldaric acid, so it must have been either D-ribose or D-xylose, since both aldaric acids formed from these have a plane of symmetry bisecting carbon 3.
   ​
The two aldohexoses formed from the Kiliani-Fischer synthesis of ribose would be D-allose and D-altrose.
   ​
The aldaric acid made from D-allose would be optically inactive, while the aldaric acid made from D-altrose would be optically active. This matches the data given. Let's look at the other possibility.
The two aldohexoses made from the Kiliani-Fischer synthesis of xylose would be D-gulose and D-idose.
   ​
The aldaric acids made from gulose and idose will both be optically active, which doesn't match the data given, so we can conclusively identify the aldopentose as D-ribose. Aldohexose A is D-allose and aldohexose B is D-altrose.

Question 3

Predict the major organic product for the reaction. If more than one isomer is formed, just draw one.

Accepted Answer

The monosaccharide will react with methanol under acidic conditions to give a cyclic acetal. None of the other hydroxy groups will be converted to an ether. Both the alpha and beta anomers will be formed.

Question 4

D-Altrose can be transformed to another aldose and 2-ketose upon treatment with base. Draw the structure of the aldose and 2-ketose.

Accepted Answer

The alpha proton can be deprotonated and

Question 5

Classify the carbohydrate, then indicate the chiral carbons with an asterisk. How many possible stereoisomers can exist for this carbohydrate?

Accepted Answer

A carbohydrate with a ketone group is ca

Question 6

Given the chair conformation of a monosaccharide, provide the open-chain form.

Accepted Answer

Translate the chair conformation to the

Question 7

Two aldohexoses (D-galactose and D-talose) are formed from a Kiliani-Fischer synthesis. Deduce the starting material.

Accepted Answer

The Kiliani-Fischer synthesis adds a car

Question 8

Identify the relationship between the two carbohydrates. Select all that apply.

Accepted Answer

A)  enantiomer 
B)  diastereomer 
C)  anomer 
D)  epimer 
A)  enantiomer 
B)  diastereomer 
C)  anomer 
D)  epimer

Question 9

Convert the line-and-wedge structure into a Fischer projection, then assign as a D- or L-carbohydrate.

Accepted Answer

You might find it easier to assign the c

Question 10

When F1F1F1S1F1F1F10-D-glucopyranose is dissolved in water, mutarotation occurs. What has happened?

Accepted Answer

A)  The carbohydrate has converted completely to F1F1F1S1F1F1F10-D-glucopyranose. 
B)  The carbohydrate has converted to a mixture of F1F1F1S1F1F1F10-D-glucopyranose and F1F1F1S1F1F1F10-D-glucopyranose. 
C)  The carbohydrate has converted to its enantiomer. 
D)  The carbohydrate has changed from D- to L-configuration. 
A)  The carbohydrate has converted completely to F1F1F1S1F1F1F10-D-glucopyranose. 
B)  The carbohydrate has converted to a mixture of F1F1F1S1F1F1F10-D-glucopyranose and F1F1F1S1F1F1F10-D-glucopyranose. 
C)  The carbohydrate has converted to its enantiomer. 
D)  The carbohydrate has changed from D- to L-configuration.

Question 11

A D-aldotetrose reacts with NaBH4 to give an optically active product. Deduce the structure of the D-aldotetrose and the product.

Accepted Answer

There are two possible D-aldotetroses, e

Question 12

Ribose is cyclized to the hemiacetal F1F1F1S1F1F1F10-D-ribofuranose. Draw a curved-arrow mechanism to show the cyclization step.

Accepted Answer

The hydroxy group on carbon 4

Question 13

Classify the carbohydrate, then indicate the chiral carbons with an asterisk. How many possible stereoisomers can exist for this carbohydrate?

Accepted Answer

A carbohydrate with an aldehyde group is

Question 14

A methyl D-glucopyranoside contains a methoxy group on which carbon of glucose? Explain the difference between a pyranoside and a pyranose.

Accepted Answer

A pyranose is a hemiacetal, wh

Question 15

Draw an enantiomer of the carbohydrate. Assign the D- or L-configuration to each.

Accepted Answer

The enantiomer is simply the mirror imag

Question 16

Identify the relationship between the two carbohydrates. Select all that apply.

Accepted Answer

A)  enantiomer 
B)  diastereomer 
C)  anomer 
D)  epimer 
A)  enantiomer 
B)  diastereomer 
C)  anomer 
D)  epimer

Question 17

The disaccharide maltose is shown below.
a. Classify the disaccharide as a reducing or nonreducing sugar and explain why.
b. Identify the glucoside linkage in maltose and classify each as either alpha or beta.
c. Name the monosaccharides formed when maltose is hydrolyzed in aqueous acid.

Accepted Answer

a. Maltose is a reducing sugar since car

Question 18

A D-aldohexose is treated with HNO3 to give an optically inactive aldaric acid. Deduce the Fischer projection of the D-aldohexose. There is more than one correct answer.

Accepted Answer

Dilute nitric acid oxidizes both primary

Question 19

Most hexoses found in nature are D-carbohydrates. Comparing a D-carbohydrate with the Cahn-Ingold-Prelog system of nomenclature, select the true statement.

Accepted Answer

A)  A D-carbohydrate will have R configuration. 
B)  A D-carbohydrate will have S configuration. 
C)  There is no relationship between the D,L system and the R/S configuration. 
A)  A D-carbohydrate will have R configuration. 
B)  A D-carbohydrate will have S configuration. 
C)  There is no relationship between the D,L system and the R/S configuration.

Question 20

Assign the R/S configuration for each of the asymmetric carbons in the carbohydrate.

Accepted Answer

Recall in a Fischer projection that the

Exam 24: Carbohydrates

The Ruff degradation of two aldopentoses gives D-threose. Deduce the structures of the two aldopentoses.

Predict the major organic product for the reaction. If more than one isomer is formed, just draw one.

D-Altrose can be transformed to another aldose and 2-ketose upon treatment with base. Draw the structure of the aldose and 2-ketose.

Classify the carbohydrate, then indicate the chiral carbons with an asterisk. How many possible stereoisomers can exist for this carbohydrate?

Given the chair conformation of a monosaccharide, provide the open-chain form.

Two aldohexoses (D-galactose and D-talose) are formed from a Kiliani-Fischer synthesis. Deduce the starting material.

Identify the relationship between the two carbohydrates. Select all that apply.

Convert the line-and-wedge structure into a Fischer projection, then assign as a D- or L-carbohydrate.

When -D-glucopyranose is dissolved in water, mutarotation occurs. What has happened?

A D-aldotetrose reacts with NaBH4 to give an optically active product. Deduce the structure of the D-aldotetrose and the product.

Ribose is cyclized to the hemiacetal -D-ribofuranose. Draw a curved-arrow mechanism to show the cyclization step.

Classify the carbohydrate, then indicate the chiral carbons with an asterisk. How many possible stereoisomers can exist for this carbohydrate?

A methyl D-glucopyranoside contains a methoxy group on which carbon of glucose? Explain the difference between a pyranoside and a pyranose.

Draw an enantiomer of the carbohydrate. Assign the D- or L-configuration to each.

Identify the relationship between the two carbohydrates. Select all that apply.

The disaccharide maltose is shown below. a. Classify the disaccharide as a reducing or nonreducing sugar and explain why. b. Identify the glucoside linkage in maltose and classify each as either alpha or beta. c. Name the monosaccharides formed when maltose is hydrolyzed in aqueous acid.

A D-aldohexose is treated with HNO3 to give an optically inactive aldaric acid. Deduce the Fischer projection of the D-aldohexose. There is more than one correct answer.

Most hexoses found in nature are D-carbohydrates. Comparing a D-carbohydrate with the Cahn-Ingold-Prelog system of nomenclature, select the true statement.

Assign the R/S configuration for each of the asymmetric carbons in the carbohydrate.

Chemical Bonding and Chemical Structure

Alkanes and Organic Nomenclature

The Curved-Arrow Notation, Resonance, Acids and Bases, and Chemical Equilibrium

Introduction to Alkenes and Alkynes

Addition Reactions of Alkenes and Alkynes

Principles of Stereochemistry

Cyclic Compounds and Reaction Stereochemistry

Nomenclature and Noncovalent Intermolecular Interactions

The Chemistry of Alkyl Halides

Free-Radical Reactions, Main-Group Organometallic Compounds, and Carbenes

The Chemistry of Alcohols and Thiols

The Chemistry of Ethers, Epoxides, Glycols, and Sulfides

Introduction to Spectroscopy

Nuclear Magnetic Resonance Spectroscopy

Dienes and Aromaticity

The Chemistry of Benzene and Its Derivatives

Allylic and Benzylic Reactivity

The Chemistry of Aryl Halides, Vinylic Halides, and Phenols

The Chemistry of Aldehydes and Ketones

The Chemistry of Carboxylic Acids

The Chemistry of Carboxylic Acid Derivatives

The Chemistry of Enolate Ions, Enols, and Α,β-Unsaturated Carbonyl Compounds

The Chemistry of Amines

The Chemistry of Thioesters, Phosphate Esters, and Phosphate Anhydrides

The Chemistry of the Aromatic Heterocycles and Nucleic Acids

Amino Acids, Peptides, and Proteins

Pericyclic Reactions

Filters

A D-aldotetrose reacts with NaBH₄ to give an optically active product. Deduce the structure of the D-aldotetrose and the product.

A D-aldohexose is treated with HNO₃ to give an optically inactive aldaric acid. Deduce the Fischer projection of the D-aldohexose. There is more than one correct answer.