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

5. Chirality

Enantiomeric Excess

Organic Chemistry

5. Chirality

Enantiomeric Excess

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2:02 minutes

Problem 63

Textbook Question

A chemist prepared a racemic mixture of the enantiomeric sulfonic acids shown here. Suggest two ways that these might be separated.

Verified step by step guidance

Understand the problem: A racemic mixture contains equal amounts of two enantiomers, which are non-superimposable mirror images of each other. The goal is to separate these enantiomers into their pure forms. This process is called resolution.

Step 1: Use a chiral resolving agent. React the racemic mixture with a chiral base or chiral alcohol to form diastereomeric salts or esters. Diastereomers have different physical properties (e.g., solubility, melting point), allowing them to be separated by physical methods such as crystallization.

Step 2: Perform chromatographic separation using a chiral stationary phase. In this method, the racemic mixture is passed through a column containing a chiral stationary phase. The enantiomers interact differently with the chiral environment, leading to their separation as they elute at different rates.

Step 3: After separation, regenerate the original enantiomers. For example, if diastereomeric salts were formed, treat them with an acid or base to recover the individual enantiomers of the sulfonic acids.

Step 4: Verify the purity of the separated enantiomers. Use techniques such as polarimetry to measure optical rotation or NMR spectroscopy with a chiral shift reagent to confirm the enantiomeric excess and purity of the separated compounds.

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Key Concepts

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

Racemic Mixture

A racemic mixture contains equal amounts of two enantiomers, which are molecules that are mirror images of each other. These compounds often exhibit different properties, particularly in chiral environments, such as biological systems. Understanding the nature of racemic mixtures is crucial for developing methods to separate enantiomers effectively.

Chiral Separation Techniques

Chiral separation techniques exploit the differences in the behavior of enantiomers in chiral environments. Common methods include chromatography using chiral stationary phases and resolution through diastereomer formation. These techniques are essential for isolating enantiomers from racemic mixtures, allowing for the study and application of each enantiomer's unique properties.

Enantiomers and Optical Activity

Enantiomers are compounds that are non-superimposable mirror images of each other and often exhibit different optical activities. This means that they rotate plane-polarized light in opposite directions, a property that can be used to distinguish between them. Understanding optical activity is vital for identifying and separating enantiomers in a racemic mixture.

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Related Practice

Textbook Question

The α- and β-anomers of glucose are shown here. In solution, these two epimers can interconvert through a process called mutarotation.

Given that α-D-glucose has a specific rotation of + 112.2° , why is the specific rotation of β-D-glucose not -112.2°? What molecule would have a specific rotation of -112.2°?

Textbook Question

Upon dissolving α-D-glucose or β-D-glucose in water, the specific rotation gradually changes, eventually reaching +52.6° for both solutions. Explain what is happening here.

Textbook Question

Questions (a)–(d) all refer to the following reaction, which has been engineered to produce one enantiomer to the exclusion of the other.

Textbook Question

How might you separate enantiomers of 2-phenylpropionic acid?

Open Question

When 0.200 g of lactose is dissolved in 10.0 ml of water and placed in a sample cell 10.0 cm in length, the observed rotation is +2°. Calculate the specific rotation of lactose.

Textbook Question

Chromatography using a chiral stationary phase is able to separate a pair of enantiomers because one of the enantiomers forms a more tightly bound complex with the stationary phase. Assuming that the (S) enantiomer elutes more slowly, rationalize this result on a reaction coordinate diagram.

Textbook Question

Figure 6.52 <IMAGE> shows the lipase-catalyzed kinetic resolution of secondary alcohols. Show a reaction coordinate diagram that rationalizes the results obtained.

Open Question

Calculate the observed rotation of a chiral mixture that contains 65% (S)-stereoisomer where the [α] of pure (S)-stereoisomer = -118.

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