Question

What other \(\mathrm{D}\) aldohexose gives the same alditol as \(\mathrm{D}\) -talose?

Short answer

D-mannose is the D-aldohexose that gives the same alditol as D-talose.

Step-by-step solution

Understand the Problem

We need to find another D-aldohexose that produces the same alditol as D-talose upon reduction. Alditols are formed when all carbons in an aldose are reduced to alcohol groups.

Visualize the Structure of D-Talose

D-talose is a six-carbon sugar (aldohexose) where the hydroxyl groups on carbons 2, 3, 4, and 5 have the stereochemistry 'left-right-right-right' if we are considering the Fischer projection. This means it's specifically an epimer of another sugar at a particular carbon.

Determine the Corresponding Alditol

When D-talose is reduced, all of its carbonyl group is reduced to an alcohol group. This means the stereochemistry of the alditol will not change from its starting sugar, just the aldehyde group is reduced to an alcohol.

Find an Epimer of D-Talose

An epimer is a sugar that differs in configuration at only one chiral center. The task is to find a D-aldohexose that is an epimer at one of the chiral carbons of D-talose, resulting in the same alditol. The most logical step is to look at changes at the fourth carbon, specifically D-mannose.

Verify the Structure of D-Mannose

D-mannose has the hydroxyl configuration 'left-left-right-right' on its 2, 3, 4, and 5 carbons, differing from D-talose only at the C-2 position, which allows it to reduce to the same alditol as D-talose.

Key concepts

alditol

Alditols are fascinating chemical compounds derived from sugars. They are the result of a reduction process where all the carbonyl groups of an aldose sugar are reduced to alcohol groups.
This transformation turns the sugar into a sugar alcohol. The key process here is converting the aldehyde group found in aldohexoses into an alcohol group.
For example, when you reduce a sugar like D-talose, you change its chemical structure while preserving its stereochemistry. Alditols are extremely useful:

• They serve as sugar substitutes, common in products like sugar-free gum.
• They are important in food industries due to their lower caloric value compared to sugars.

By understanding alditols, we can better comprehend the chemical behavior of sugars upon reduction.

D-talose

D-talose is a lesser-known but interesting sugar known as an aldohexose. It has six carbon atoms with an aldehyde group at one end.
The hydroxyl groups attached to its carbon chain follow a "left-right-right-right" pattern when drawn using the Fischer projection, making it unique. A few key points about D-talose include:

• It is a stereoisomer with various uses in biochemical research.
• It forms specific alditols when reduced, maintaining its stereochemistry.

D-talose is an epimer of several other aldohexoses, meaning it only differs from them by the configuration at one carbon atom.

epimer

Epimers are a fascinating type of stereoisomer, which are molecules that have the same formula but a different arrangement of atoms in space. Specifically, epimers differ at just one chiral center of their carbon chain.
This tiny change can lead to significant differences in properties and behavior of sugars. For instance, D-talose and D-mannose are epimers of each other. Their distinction lies at the second carbon (C-2) in their chain.
This small change allows these sugars to form the same alditol upon reduction. Understanding epimers is vital because:

• It helps predict reactions between similar molecules.
• It demonstrates the delicate balance of stereochemistry in sugars.

Recognizing epimers gives insight into the subtle, yet impactful details of sugar structure.

D-mannose

D-mannose is another aldohexose, much like D-talose, and is well-known in both biological and chemical contexts. Its structure is distinguishable by its "left-left-right-right" pattern of hydroxyl groups on carbons 2 to 5 in the Fischer projection.
This setup makes D-mannose an epimer of D-talose, differing only at the second carbon in the chain. D-mannose has its own set of important attributes:

• It's naturally occurring and plays a crucial role in human health, often linked with urinary tract health.
• When reduced, it yields the same alditol as D-talose, demonstrating the impact of stereochemistry.

Knowing about D-mannose helps understand the diversity of sugar structures and their implications in health and industry.