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

Constitutional Isomers vs. Stereoisomers

Organic Chemistry

5. Chirality

Constitutional Isomers vs. Stereoisomers

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3:44 minutes

Problem 75

Textbook Question

For many centuries, the Chinese have used extracts from a group of herbs known as ephedra to treat asthma. A compound named ephedrine has been isolated from these herbs and found to be a potent dilator of air passages in the lungs.
a. How many stereoisomers does ephedrine have?
b. The stereoisomer shown here is the one that is pharmacologically active. What is the configuration of each of the asymmetric centers?

Verified step by step guidance

Step 1: Identify the asymmetric centers in the structure of ephedrine. An asymmetric center is a carbon atom bonded to four different groups. In the given structure, there are two asymmetric centers: one is the carbon attached to the hydroxyl group (-OH), the phenyl group, a hydrogen atom, and the rest of the chain; the other is the carbon attached to the amino group (-NH2), a methyl group (-CH3), a hydrogen atom, and the rest of the chain.

Step 2: Determine the number of stereoisomers possible for ephedrine. The formula for calculating the number of stereoisomers is 2^n, where n is the number of asymmetric centers. Since ephedrine has two asymmetric centers, the number of stereoisomers is 2^2 = 4.

Step 3: Analyze the configuration of each asymmetric center in the given stereoisomer. To assign the configuration (R or S), use the Cahn-Ingold-Prelog priority rules: assign priorities to the groups attached to the asymmetric center based on atomic number, and determine the spatial arrangement of these groups.

Step 4: For the first asymmetric center (carbon attached to -OH), assign priorities to the groups: phenyl group > hydroxyl group (-OH) > the rest of the chain > hydrogen. Determine the configuration by observing the arrangement of these groups in the given structure.

Step 5: For the second asymmetric center (carbon attached to -NH2), assign priorities to the groups: amino group (-NH2) > methyl group (-CH3) > the rest of the chain > hydrogen. Determine the configuration by observing the arrangement of these groups in the given structure.

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Key Concepts

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

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. This can lead to different physical and chemical properties. In the case of ephedrine, it has multiple stereocenters, resulting in several stereoisomers, which can have varying biological activities.

Chirality and Asymmetric Centers

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of asymmetric centers (chiral centers). Each asymmetric center in a molecule can have two configurations, typically designated as R (rectus) or S (sinister). Understanding the configuration of these centers is crucial for determining the pharmacological activity of compounds like ephedrine.

Pharmacologically Active Stereoisomers

Pharmacologically active stereoisomers are specific stereoisomers of a compound that exhibit the desired therapeutic effects in biological systems. In the case of ephedrine, only one stereoisomer is responsible for its effectiveness as a bronchodilator. Identifying and understanding the configuration of this active stereoisomer is essential for drug development and therapeutic applications.

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For each of the following chiral molecules, obtain the enantiomer (i) by drawing the nonsuperimposable mirror image and (ii) by switching the spatial orientation at each asymmetric center. Confirm (possibly using models) that the structures you drew for (i) and (ii) are the same.

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How many stereoisomers are possible for each of the following molecules?

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Textbook Question

How many stereoisomers are possible for each of the following molecules?

(c)

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Draw a three-dimensional structure for each compound, and star all asymmetric carbon atoms. Draw the mirror for each structure, and state whether you have drawn a pair of enantiomers or just the same molecule twice. Build molecular models of any of these examples that seem difficult to you

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Draw the stereoisomers of the following amino acids. Indicate pairs of enantiomers and pairs of diastereomers.

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