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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1:34 minutes

Problem 77

Textbook Question

Is the compound d or l?

Verified step by step guidance

Step 1: Understand the concept of optical isomerism. Optical isomers, also known as enantiomers, are molecules that are mirror images of each other and cannot be superimposed. They are designated as 'd' (dextrorotatory) or 'l' (levorotatory) based on the direction they rotate plane-polarized light.

Step 2: Identify the chiral center in the compound. A chiral center is typically a carbon atom bonded to four different groups. This is crucial for determining the optical activity of the compound.

Step 3: Assign priorities to the substituents attached to the chiral center using the Cahn-Ingold-Prelog priority rules. The substituent with the highest atomic number gets the highest priority.

Step 4: Determine the configuration of the chiral center. Arrange the molecule so that the lowest priority group is pointing away from you. Then, observe the order of the remaining groups. If the sequence is clockwise, the configuration is 'R'; if counterclockwise, it is 'S'.

Step 5: Relate the configuration to optical activity. While 'R' and 'S' configurations do not directly indicate 'd' or 'l', experimental determination of optical rotation is required. If the compound rotates light to the right, it is 'd'; if to the left, it is 'l'.

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Key Concepts

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

Chirality

Chirality refers to the geometric property of a molecule having a non-superimposable mirror image, much like left and right hands. In organic chemistry, chiral molecules typically have a carbon atom bonded to four different groups, creating two enantiomers that are mirror images of each other. Understanding chirality is essential for determining the optical activity of compounds.

Fischer Projection

The Fischer projection is a two-dimensional representation of a three-dimensional organic molecule used to depict stereochemistry. It is particularly useful for carbohydrates and amino acids, where horizontal lines represent bonds coming out of the plane, and vertical lines represent bonds going into the plane. This projection helps in identifying the configuration of chiral centers as D or L.

D and L Configuration

The D and L configuration system is used to denote the absolute configuration of chiral molecules, particularly sugars and amino acids. It is based on the orientation of the hydroxyl group on the chiral carbon farthest from the carbonyl group in Fischer projections. If the hydroxyl group is on the right, the molecule is D; if on the left, it is L. This system is crucial for understanding the stereochemistry of biomolecules.

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Related Practice

Textbook Question

c. Draw d-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.

d. Draw the C4 “epimer” of D-xylose. Notice that this “epimer” is actually an L-series sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.

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):

Textbook Question

Categorize the following monosaccharides as d or l.

(a)

Textbook Question

Starting with a Fischer projection of d-glucose (and other sugars), switch only the stereocenter that gave it the designation of d. What new sugar have you made? [Hint: The answer is not l-glucose.]

Multiple Choice

How many stereoisomers are possible for a 2-ketohexose, considering D and L isomerism?

Multiple Choice

Provide the generic name, including stereochemistry, for the following monosaccharide:

Multiple Choice

Which of the following depicts a D-sugar?

Textbook Question

c. Draw d-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.

d. Draw the C4 “epimer” of D-xylose. Notice that this “epimer” is actually an L-series sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.

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