In Section 15.6, you saw that aldehydes react with reducing agents to yield primary alcohols (RCH=O → RCH 2 OH). The structures of two D-aldotetroses are shown. One of them can be reduced to yield a chiral product, but the other yields an achiral product. Explain.

Hello, everyone. Today, we have the following problem. Aldehydes are converted to primary alcohols. When reacted with a reducing agent, consider the two Aldo hexes shown below. When both of them are reduced, one gives a cro product and the other gives an ayro product. Explain. So if we reduce both of these, starting with galactose, the aldehyde will become a primary alcohol group and the rest of the molecule remains unchanged. If we take the Talos and reduce it, the aldehyde once again becomes a primary alcohol and the rest of the molecule remains unchanged. So what is the difference between these two? Well, both of them, both of the reduced products have four chiral centers. However, the reduced product of D galactose essentially has an internal plane of symmetry. And because of this, it is considered a meso compound and therefore a chiral. On the other hand, there is no internal plan of symmetry with the reduced product of the Talos. And so with that, we have solved the problem overall, I hope this helped. And until next time

Table of contents

Skip topic navigation

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

20. Carbohydrates

Reduction of Monosaccharides

GOB Chemistry

20. Carbohydrates

Reduction of Monosaccharides

Previous problemNext problem

1:48 minutes

Problem 41

Textbook Question

In Section 15.6, you saw that aldehydes react with reducing agents to yield primary alcohols (RCH=O → RCH₂OH). The structures of two D-aldotetroses are shown. One of them can be reduced to yield a chiral product, but the other yields an achiral product. Explain.

Verified step by step guidance

Step 1: Understand the reaction. Aldehydes (RCH=O) react with reducing agents to form primary alcohols (RCH₂OH). This involves the addition of hydrogen to the carbonyl group, converting the double bond to a single bond and adding a hydroxyl group (-OH) to the carbon.

Step 2: Analyze the structures of the two d-aldotetroses. Aldotetroses are four-carbon sugars with an aldehyde group at one end and hydroxyl groups attached to the other carbons. The chirality of the product depends on the symmetry of the molecule after reduction.

Step 3: Consider the concept of chirality. A molecule is chiral if it has a non-superimposable mirror image, often due to the presence of a carbon atom bonded to four different groups. If the product has a plane of symmetry, it will be achiral.

Step 4: Examine the reduction process. When the aldehyde group is reduced to a primary alcohol, the resulting molecule will have a hydroxyl group (-OH) at the end. For one of the d-aldotetroses, this reduction creates a molecule with a plane of symmetry, making it achiral. For the other, the reduction does not introduce symmetry, so the product remains chiral.

Step 5: Identify the specific d-aldotetroses. The d-aldotetrose that yields an achiral product likely has a symmetric arrangement of hydroxyl groups after reduction, while the one that yields a chiral product has an asymmetric arrangement. Carefully compare the structures of the two d-aldotetroses to determine which is which.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Aldehyde Reduction

Aldehyde reduction is a chemical reaction where an aldehyde (RCH=O) is converted into a primary alcohol (RCH₂OH) through the addition of hydrogen or a reducing agent. This process is significant in organic chemistry as it alters the functional group of the molecule, impacting its reactivity and properties. The stereochemistry of the resulting alcohol can vary depending on the structure of the aldehyde and the conditions of the reaction.

Chirality

Chirality refers to the geometric property of a molecule having non-superimposable mirror images, much like left and right hands. A chiral molecule typically has at least one carbon atom bonded to four different substituents, leading to two distinct enantiomers. In the context of aldehyde reduction, the formation of a chiral product indicates that the reduction process creates a new stereocenter, which can result in two different optical isomers.

Achirality

Achirality describes molecules that are superimposable on their mirror images, meaning they do not have a chiral center. Such molecules can be symmetrical or have identical substituents around a central atom, leading to a single form without enantiomers. In the case of aldehyde reduction, if the starting aldehyde is achiral, the resulting alcohol will also be achiral, as the reduction does not introduce any new stereocenters.

Watch next

Master Reduction of Monosaccharides Concept 1 with a bite sized video explanation from Jules

Start learning