Ch.6 Carbohydrates Life's Sweet Molecules

Frost - General, Organic and Biological Chemistry 4th Edition

Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Not the one you use?Change textbook

Frost 4th Edition

Ch.6 Carbohydrates Life's Sweet Molecules

Problem 67a

Chapter 3, Problem 67a

Identify the following carbohydrates as the ⍺ or β anomer:
(a)

Verified step by step guidance

Examine the structure of the carbohydrate provided in the image. Focus on the orientation of the hydroxyl group (-OH) attached to the anomeric carbon (the carbon derived from the carbonyl group in the cyclic form).

Determine the position of the hydroxyl group relative to the ring. If the hydroxyl group is pointing down (on the opposite side of the ring from the CH2OH group), it is the α-anomer. If it is pointing up (on the same side as the CH2OH group), it is the ß-anomer.

Identify the anomeric carbon in the cyclic structure. This is typically the carbon bonded to two oxygen atoms: one in the ring and one in the hydroxyl group.

Compare the orientation of the hydroxyl group on the anomeric carbon to the CH2OH group attached to the ring. Use the α/ß distinction based on their relative positions.

Label the carbohydrate as either the α or ß anomer based on your observations from the previous steps.

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Key Concepts

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

Anomers

Anomers are a type of stereoisomer found in carbohydrates that differ in configuration at the anomeric carbon, which is the carbon derived from the carbonyl group during cyclization. In cyclic forms of sugars, the anomeric carbon can be in two configurations: alpha (α) when the hydroxyl group is on the opposite side of the CH2OH group, and beta (β) when it is on the same side. This distinction is crucial for understanding the reactivity and properties of sugars.

Cyclic Forms of Carbohydrates

Carbohydrates can exist in linear and cyclic forms, with the cyclic form being more stable in aqueous solutions. The formation of a cyclic structure occurs when the carbonyl group reacts with a hydroxyl group, leading to the creation of a ring. This process involves the formation of an anomeric carbon, which is key to determining whether the carbohydrate is in its α or β form.

Haworth Projection

The Haworth projection is a common way to represent the cyclic structures of carbohydrates, providing a clear visualization of the orientation of substituents around the ring. In this representation, the anomeric carbon is typically at the right side of the ring, allowing for easy identification of the α or β configuration based on the position of the hydroxyl group. Understanding this projection is essential for accurately identifying anomers in carbohydrate structures.

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Guided course

2:18

Intro to Haworth Projections Concept 1

Related Practice

Textbook Question

How are the following pairs of carbohydrates, shown in a Fischer projection, related to each other? Are they structural isomers, enantiomers, diastereomers, or epimers? Identify each as the D- or L-isomer.

(b)

Textbook Question

How are the following pairs of carbohydrates, shown in a Fischer projection, related to each other? Are they structural isomers, enantiomers, diastereomers, or epimers?

(a)

Textbook Question

Draw the Fischer projection of the C3 epimer of D-glucose. Compare your structure with those in Table 6.1 and give the name of this compound.

Textbook Question

Identify the following carbohydrates as the ⍺ or β anomer:

(b)

Textbook Question

Draw the Fischer projection of the product of the oxidation of D-galactose at C1.

Textbook Question

Draw the Fischer projection of the product of reduction reaction of D-galactose at C1.