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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1:09 minutes

Problem 36c

Textbook Question

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

Verified step by step guidance

Identify the number of stereocenters (chiral centers) in the molecule. A stereocenter is typically a carbon atom bonded to four different groups.

Use the formula for calculating the maximum number of stereoisomers: \( 2^n \), where \( n \) is the number of stereocenters in the molecule.

Check for any elements of symmetry in the molecule, such as a plane of symmetry or a center of symmetry. Symmetry can reduce the number of stereoisomers because some configurations may be identical.

Determine if the molecule contains any double bonds with restricted rotation (e.g., \( C=C \) bonds). If so, consider the possibility of cis-trans (geometric) isomerism, which can also contribute to the total number of stereoisomers.

Combine the information from the stereocenters and any geometric isomerism to calculate the total number of stereoisomers. Adjust for symmetry if applicable.

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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 those atoms. This can lead to different physical and chemical properties. The two main types of stereoisomers are enantiomers, which are non-superimposable mirror images, and diastereomers, which are not mirror images of each other.

Chirality

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of a chiral center, typically a carbon atom bonded to four different substituents. Molecules that are chiral can exist as two enantiomers, which can have significantly different biological activities. Identifying chiral centers is crucial for determining the number of stereoisomers.

Calculating Stereoisomers

The number of possible stereoisomers for a molecule can be calculated using the formula 2^n, where n is the number of chiral centers in the molecule. This formula assumes that all chiral centers are independent and can exist in both configurations (R and S). For molecules with additional elements of symmetry, the actual number of stereoisomers may be less than the maximum calculated using this formula.

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Related Practice

Textbook Question

Draw all the stereoisomers for each of the following:

e. 3,4-dichlorohexane

f. 1,2-dichlorocyclobutane

Textbook Question

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.

(d)

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?

Textbook Question

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

(a)

Textbook Question

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

(a)

(b)

Textbook Question

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

Textbook Question

Which of the following pairs of compounds could be separated by recrystallization or distillation?

a. meso-tartaric acid and (±)-tartaric acid (HOOC—CHOH—CHOH—COOH)

Textbook Question

Draw the enantiomer, if any, for each structure.

(e)

(f)

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