Chemistry: Diastereomers and Cyclic Structures

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Questions and Answers

What defines diastereomers in terms of chiral centers?

They are mirror images of each other.

They differ at every chiral center.

They have opposite configurations at one or more chiral centers. (correct)

They have the same configuration at all chiral centers.

Which monosaccharides are considered C-2 epimers?

Glucose and Galactose

Galactose and Fructose

Glucose and Mannose (correct)

Mannose and Galactose

What is formed when an aldehyde reacts with an alcohol?

Hemiacetal (correct)

Acid

Carboxylate

Ketal

Which ring structure is formed primarily by monosaccharides with five or more carbon atoms?

Furanose Signup and view all the answers

What type of projection shows the three-dimensional structure of ring forms of monosaccharides more realistically?

Haworth projection Signup and view all the answers

Why are Fischer projection formulas considered unrealistic for representing certain carbohydrates?

They use elongated bent lines that complicate visualization. Signup and view all the answers

What does the term 'anomer' refer to in carbohydrate chemistry?

Isomers that differ at the anomeric carbon Signup and view all the answers

Which statement correctly describes the characteristics of furanoses?

They resemble the five-membered ring compound furan. Signup and view all the answers

What happens to reducing sugars when they react with cupperic solution?

They oxidize to sugar acids. Signup and view all the answers

Which of the following compounds is formed from the reduction of glucose?

Glucitol Signup and view all the answers

What is the primary feature of amino sugars like D-glucosamine?

They replace the hydroxyl group with an amino group at C-2. Signup and view all the answers

What is produced during the fermentation of glucose?

Ethanol and carbon dioxide Signup and view all the answers

What type of reaction leads to the formation of lactones from aldonic acids?

Condensation Signup and view all the answers

Which of the following statements is true regarding phosphate esters of carbohydrates?

They enhance the solubility of carbohydrates. Signup and view all the answers

Which of the following sugars is not a reducing sugar?

Sucrose Signup and view all the answers

What change occurs to the chemical properties of a sugar when it undergoes esterification?

It becomes less soluble in water. Signup and view all the answers

What characterizes the configuration at the anomeric carbon in α-D-glucose?

The hydroxyl group at the anomeric carbon is on the same side as the distant asymmetric carbon. Signup and view all the answers

How many stereoisomers can D-glucose and D-fructose form in their Haworth projections?

Two each Signup and view all the answers

What is mutarotation in relation to sugars?

The process where α and β anomers of a sugar are in equilibrium. Signup and view all the answers

In the Haworth projection of D-glucose, where do the OH groups that are on the right in a Fischer projection appear?

Below the ring level Signup and view all the answers

What type of bond is associated with axial positions in a pyranose ring?

Bonds projecting parallel to the vertical axis Signup and view all the answers

Which of the following correctly describes anomers?

Isomers that differ only at the anomeric carbon. Signup and view all the answers

What is the orientation of the -OH group at the anomeric carbon in β-D-glucose?

It is above the plane in the Haworth projection. Signup and view all the answers

Which conformation of a six-membered ring is NOT typically associated with the pyranose form?

Tetrahedral Signup and view all the answers

Study Notes

Diastereomers

Diastereomers are isomers with opposite configurations at one or more chiral centers but are not mirror images.
Example: Glucose and Galactose

Epimers

Epimers are diastereomers that differ in configuration at only one specific carbon atom.

Anomers and Cyclic Structures

Aldotetroses and monosaccharides with 5 or more carbon atoms primarily exist as cyclic structures in aqueous solution.
These ring structures are formed through reactions between alcohols and aldehydes or ketones to form hemiacetals or hemiketals, which have an additional asymmetric carbon atom.

Haworth Projection Formulas

Haworth projections are used to represent the three-dimensional structure of cyclic monosaccharides.
Six-membered rings are called pyranoses and resemble pyran.
Five-membered rings are called furanoses and resemble furan.
Haworth projections show the ring lying perpendicular to the plane of the paper with thickened lines indicating the side closest to the viewer.

Anomers

Anomers are isomeric forms of monosaccharides that differ in configuration only at the hemiacetal or hemiketal carbon.
The hemiacetal or carbonyl carbon is called the anomeric carbon.

Mutarotation

Mutarotation is the spontaneous interconversion between cyclic α and β anomers of a sugar in solution.

Conformational Isomers

Conformational isomers are interconvertible by rotation around a single bond without breaking covalent bonds.
Pyranose rings can exist in chair and boat conformations.

Axial and Equatorial Bonds

Axial bonds project parallel to the vertical axis through the ring.
Equatorial bonds project perpendicular to the axis.

Oxidation Reaction

Reducing sugars can reduce oxidizing agents like peroxide, ferricyanide, and some metals (Cu and Ag).
They reduce cupperic solution (Cu⁺²) to cupperous solution (Cu⁺¹) .
This redox reaction converts the sugar to a sugar acid.
Glucose is a reducing sugar.

Lactone

The carboxyl group of an aldonic acid can react with an -OH group in the same molecule to form a cyclic ester called a lactone.

Sugar Alcohols Reduction Reaction

Reduction of the aldehyde and ketone groups of a monosaccharide yields sugar alcohols (alditols).
Sugar alcohols are used in food processing and pharmaceuticals.

Amino Sugars

Amino sugars contain an amino group at the C-2 position instead of a hydroxyl group.
They are found in oligo- and polysaccharides, including chitin.

Esterification

Free -OH groups in carbohydrates can be converted to esters by reaction with acids.
Phosphate and sulfate esters of carbohydrates are common in nature.

Fermentation Reaction

Fermentation is a process catalyzed by enzymes.
An example is the conversion of glucose to ethanol and carbon dioxide.

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Description

This quiz explores the concepts of diastereomers, epimers, and the formation of cyclic structures in monosaccharides. Learn how Haworth projections are used to visualize these compounds and their configurations. Test your understanding of stereochemistry and carbohydrate structures!