Ch.6 Carbohydrates Life's Sweet Molecules

Frost - General, Organic and Biological Chemistry 4th Edition

Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Non è quello che usi tu?Cambia libro di testo

Frost 4th Edition

Ch.6 Carbohydrates Life's Sweet Molecules

Problema 92

Capitolo 3, Problema 92

D-Fructose can also form a six-membered ring. Draw the β anomer of D-fructose in the six-membered ring form.

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Understand that d-fructose is a ketohexose, meaning it contains six carbon atoms and a ketone functional group. In aqueous solutions, it can cyclize to form a six-membered ring structure called a pyranose.

Identify the key functional groups in d-fructose: the ketone group at carbon 2 and hydroxyl groups on other carbons. These groups participate in the cyclization reaction.

Recognize that the six-membered ring forms when the hydroxyl group on carbon 6 reacts with the ketone group on carbon 2, creating a hemiacetal linkage.

Determine the anomeric configuration: The newly formed hydroxyl group at the anomeric carbon (carbon 2) can be either axial (α-anomer) or equatorial (β-anomer) in the ring structure. This depends on the orientation of the hydroxyl group relative to the ring plane.

Draw the six-membered ring structure (pyranose form) of d-fructose, ensuring the correct placement of substituents on each carbon atom and indicating the α or β configuration at the anomeric carbon.

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Anomer

An anomer is a type of stereoisomer that differs at the anomeric carbon, which is the carbon atom that becomes a new chiral center when a sugar cyclizes. In the case of d-fructose, the anomeric carbon is the one that is part of the carbonyl group in its open-chain form. The two anomers are designated as alpha (α) and beta (β) based on the orientation of the hydroxyl group attached to the anomeric carbon.

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2:49

Cyclic Structures of Monosaccharides Concept 1

Cyclization of Sugars

Cyclization is the process by which a linear sugar molecule forms a cyclic structure, typically a five- or six-membered ring. For d-fructose, this involves the reaction of the carbonyl group with a hydroxyl group on the same molecule, leading to the formation of a hemiacetal. This transformation is crucial for the stability and reactivity of sugars in biological systems.

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1:01

Ketoses as Reducing Sugars Example 2

Haworth Projection

The Haworth projection is a common way to represent the cyclic forms of sugars, showing the ring structure in a two-dimensional format. In this representation, the orientation of substituents (like hydroxyl groups) is depicted clearly, allowing for easy identification of anomers. For d-fructose, drawing its six-membered ring in a Haworth projection helps visualize the spatial arrangement of its functional groups.

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2:18

Intro to Haworth Projections Concept 1

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