Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives

Problem 86a

Chapter 17, Problem 86a

In an aqueous solution, D-glucose exists in equilibrium with two six-membered ring compounds. Draw the structures of these compounds.

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Understand that D-glucose is an aldohexose, meaning it contains an aldehyde group and six carbon atoms. In aqueous solution, it undergoes intramolecular cyclization to form cyclic hemiacetals.

Recognize that the cyclization occurs when the hydroxyl group on carbon-5 (C-5) reacts with the aldehyde group on carbon-1 (C-1), forming a six-membered ring structure called a pyranose.

Identify that the cyclization creates a new stereocenter at C-1, known as the anomeric carbon. This results in two possible stereoisomers: the alpha (α) anomer and the beta (β) anomer.

Draw the structure of the α-D-glucopyranose, where the hydroxyl group attached to the anomeric carbon (C-1) is positioned *axially* (down) relative to the ring plane.

Draw the structure of the β-D-glucopyranose, where the hydroxyl group attached to the anomeric carbon (C-1) is positioned *equatorially* (up) relative to the ring plane.

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Key Concepts

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

Anomeric Carbon

The anomeric carbon is the carbon atom in a sugar molecule that is derived from the carbonyl carbon of the open-chain form. In cyclic forms of sugars, it is the carbon that determines the alpha or beta configuration, depending on whether the hydroxyl group is positioned below or above the plane of the ring. Understanding this concept is crucial for drawing the correct structures of d-glucose's cyclic forms.

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. It illustrates the orientation of substituents around the ring, making it easier to visualize the stereochemistry of the molecule. This representation is essential for accurately drawing the six-membered ring compounds of d-glucose.

Mutarotation

Mutarotation is the process by which the optical rotation of a sugar solution changes over time as the sugar equilibrates between its anomeric forms. For d-glucose, this involves the interconversion between alpha and beta anomers in solution. Understanding mutarotation is important for recognizing the dynamic nature of sugar structures in aqueous environments.

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Mechanism

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Textbook Question

Propose a mechanism for each of the following reactions:

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Textbook Question

In the presence of an acid catalyst, acetaldehyde forms a trimer known as paraldehyde. Because it induces sleep when it is administered to animals in large doses, paraldehyde is used as a sedative or hypnotic. Propose a mechanism for the formation of paraldehyde.

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Textbook Question

How can the following compounds be prepared from the given starting materials?

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Textbook Question

Shown below is the ¹H NMR spectrum of the alkyl bromide used to make the phosphonium ylide that reacts with a ketone in a Wittig reaction to form a compound with molecular formula C₁₁H₁₄. What product is obtained from the Wittig reaction?

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Textbook Question

What carbonyl compound and what phosphonium ylide are needed to synthesize the following compounds?

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Textbook Question

Propose a mechanism for each of the following reactions:

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