Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

28. Carbohydrates

Monosaccharides - D and L Isomerism

Organic Chemistry

28. Carbohydrates

Monosaccharides - D and L Isomerism

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2:02 minutes

Problem 3

Textbook Question

Indicate whether each of the following structures is D-glyceraldehyde or L-glyceraldehyde, assuming that the horizontal bonds point toward you and the vertical bonds point away from you (Section 4.7):
a.
b.
c.

Verified step by step guidance

Step 1: Recall the Fischer projection convention. In a Fischer projection, horizontal bonds represent groups pointing toward the viewer, while vertical bonds represent groups pointing away from the viewer.

Step 2: Identify the chiral center in glyceraldehyde. Glyceraldehyde has one chiral center, which is the carbon atom bonded to the hydroxyl group (-OH), the hydrogen atom (H), and the aldehyde group (-CHO).

Step 3: Determine the configuration of the chiral center. Assign priorities to the substituents based on the Cahn-Ingold-Prelog rules: (1) -CHO, (2) -OH, (3) -CH2OH, and (4) H.

Step 4: Analyze the arrangement of the substituents. If the -OH group is on the right side of the Fischer projection, the molecule is d-glyceraldehyde. If the -OH group is on the left side, the molecule is l-glyceraldehyde.

Step 5: Apply the above rules to each structure (a, b, c) provided in the problem. Carefully inspect the position of the -OH group in each Fischer projection to classify them as d-glyceraldehyde or l-glyceraldehyde.

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Key Concepts

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

D and L Configuration

The D and L notation refers to the configuration of chiral centers in sugars. It is based on the orientation of the hydroxyl group (-OH) on the penultimate carbon (the second to last carbon) in the molecule. If the -OH group is on the right side in a Fischer projection, the sugar is designated as D; if it is on the left, it is designated as L.

Fischer Projection

A Fischer projection is a two-dimensional representation of a three-dimensional organic molecule, particularly useful for depicting carbohydrates. In this representation, vertical lines represent bonds that project away from the viewer, while horizontal lines represent bonds that come toward the viewer. Understanding how to interpret Fischer projections is essential for determining the D or L configuration of sugars.

Chirality and Stereoisomers

Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, leading to the existence of stereoisomers. In the case of glyceraldehyde, there are two enantiomers: D-glyceraldehyde and L-glyceraldehyde, which differ in the spatial arrangement of their atoms. Recognizing chirality is crucial for understanding the behavior and reactivity of organic compounds, especially in biological systems.

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