Question

Which of the other three D aldopentoses gives the same aldaric acid as D-lyxose?

Short answer

D-xylose gives the same aldaric acid as D-lyxose.

Step-by-step solution

Understand Aldopentoses

Aldopentoses are five-carbon sugars with an aldehyde group. They have four stereocenters, creating different stereoisomers. In D-configuration, they have specific orientation around the third carbon (C3). The common D-aldopentoses are D-ribose, D-arabinose, D-xylose, and D-lyxose.

Oxidation of D-Lyxose into Aldaric Acid

Convert D-lyxose into the corresponding aldaric acid by oxidizing both the aldehyde group and the primary alcohol group to carboxylic acids. This gives the aldaric acid derived from D-lyxose.

Configuration of Aldaric Acid

Recognize that when D-lyxose is oxidized, it results in meso-tartaric acid, due to symmetrical configuration around the central carbon atom in the sugar's aldaric acid form.

Determine Other Aldopentoses Conversion

Determine which other D-aldopentose can be oxidized to form the same symmetrical meso-tartaric acid. To do this, analyze the configurations of other D-aldopentoses for similar symmetry around the central carbon after oxidation.

Compare D-Xylose and Meso Formation

Understand that D-xylose, when both ends are oxidized, also becomes the same meso-tartaric acid, due to its particular stereochemical structure. This similarity in symmetry makes D-xylose a match.

Key concepts

D-aldopentoses

D-aldopentoses are sugars that consist of five carbon atoms with an aldehyde group functioning as a pivotal feature. This group of carbohydrates is distinguished by the specific configuration of hydroxyl groups attached to the carbon skeleton, based on the direction they point. Each D-aldopentose molecule includes four stereocenters, also known as chiral centers. These create variations or stereoisomers of the sugar, making them diverse in structure and orientation.
The 'D' in D-aldopentoses indicates the arrangement of the hydroxyl group at the chiral center farthest from the aldehyde group. In practical terms, it implies a specific stereochemical layout around the third carbon (C3).
A few common examples of these sugars include:

• D-ribose
• D-arabinose
• D-xylose
• D-lyxose

These sugars are not only structural peers but also vary in functional qualities based on their stereochemistry. This property leads to intriguing transformations when exposed to certain reactions, particularly oxidation.

Oxidation of sugars

Oxidation of sugars is a chemical process wherein the aldehyde group and the primary alcohol group of a sugar are converted into carboxylic acids. This transformation is crucial in understanding how aldopentoses like D-lyxose become aldaric acids.
In oxidation, D-lyxose undergoes a chemical reaction that reforms its structure. Both the aldehyde group at one end and the primary hydroxyl group at the other end are oxidized into carboxylic acids, resulting in an aldaric acid. Specifically, oxidation of sugars can lead to the formation of unique compounds such as meso-tartaric acid.
This acid is a product of symmetrical oxidation due to its stereo arrangement, which means that despite the changes at the molecular level, some aspects of symmetry are retained or produced. Understanding which other aldopentoses can form the same aldaric acid involves examining these reactions and recognizing the similarity or difference in stereochemistry leading to analogous products.

Stereochemistry in organic chemistry

Stereochemistry is the study of how molecules are spatially arranged, which is crucial in understanding the reactivity and interaction of organic compounds. In the context of sugars and their derivatives, stereochemistry determines how these substances behave under different conditions, such as during oxidation processes.
For D-aldopentoses, the stereochemical configuration helps predict the outcome of oxidation. When D-lyxose, for instance, undergoes oxidation, it forms a meso-tartaric acid. This is linked to its symmetrical molecular structure, as the stereochemistry ensures the formation of a meso compound, which is achiral despite containing stereocenters.
A crucial role of stereochemistry comes to light when comparing different sugars like D-lyxose and D-xylose. Both can yield the same meso-tartaric acid upon oxidation due to their stereochemical similarities around the central carbon atom. Thus, understanding the basics of stereochemistry is significant in determining which sugars result in identical aldaric acids after oxidation. Keeping track of the spatial arrangement of groups in these molecules is essential for predicting their chemical behavior.