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

Test 2:Stereocenter Test

Organic Chemistry

5. Chirality

Test 2:Stereocenter Test

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8:19 minutes

Problem 63

Textbook Question

Explain why compound A has two stereoisomers but compounds B and C exist as single compounds.

Verified step by step guidance

Step 1: Analyze the structures of compounds A, B, and C. Compound A has a positively charged nitrogen atom bonded to four different groups: a methyl group, a hydrogen atom, an ethyl group, and a carbonyl group. This makes the nitrogen atom a stereogenic center, allowing for two stereoisomers (R and S configurations).

Step 2: Examine compound B. The nitrogen atom in compound B is also positively charged and bonded to four different groups: a methyl group, a hydrogen atom, another methyl group, and a carbonyl group. However, two of the groups are identical (methyl groups), which means the nitrogen atom is not a stereogenic center, and compound B exists as a single compound.

Step 3: Evaluate compound C. The nitrogen atom in compound C is neutral and has a lone pair of electrons. It is bonded to three groups: a methyl group, a hydrogen atom, and a carbonyl group. Since the nitrogen atom is sp2 hybridized and planar, it does not have a stereogenic center, and compound C exists as a single compound.

Step 4: Understand the concept of stereoisomers. Stereoisomers arise when a molecule has a stereogenic center (a carbon or nitrogen atom bonded to four different groups) and can exist in two non-superimposable mirror image forms. Compound A meets this criterion, while compounds B and C do not.

Step 5: Summarize the reasoning. Compound A has two stereoisomers due to the presence of a stereogenic nitrogen atom bonded to four different groups. Compound B lacks stereoisomers because it has two identical groups bonded to the nitrogen atom, and compound C lacks stereoisomers because its nitrogen atom is planar and not stereogenic.

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Key Concepts

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

Stereoisomerism

Stereoisomerism occurs when 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. Compounds A has two stereoisomers due to the presence of a chiral center, which allows for non-superimposable mirror images.

Chirality

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of a carbon atom bonded to four different substituents. In compound A, the nitrogen atom creates a chiral center, leading to two distinct stereoisomers. In contrast, compounds B and C lack such chiral centers, resulting in only one form.

Geometric Isomerism

Geometric isomerism, a subtype of stereoisomerism, arises from the restricted rotation around a double bond or a ring structure, leading to different spatial arrangements of substituents. Compounds B and C may have double bonds or cyclic structures that do not allow for geometric isomerism, thus existing as single compounds without stereoisomers.

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Related Practice

Textbook Question

Identify the following molecules as chiral or achiral. If chiral, draw the nonsuperimposable mirror image and verify its nonsuperimposability.

(f)

Multiple Choice

Which of the following atoms are stereocenters?

Textbook Question

Which of the following has an asymmetric center?

CHBr₂Cl, BHFCl, CH₃CHCl₂, CHFBrCl, BeHCl

Textbook Question

Of all the possible cyclooctanes that have one chloro substituent and one methyl substituent, which ones do not have any asymmetric centers?

Textbook Question

The following four structures are naturally occurring optically active compounds. Star (*) the asymmetric carbon atoms in these structures.

Textbook Question

A molecule of the type shown here is discussed in greater detail in Section 6.5.1. Draw the mirror image. Is it superimposable? Switch the spatial orientation at both asymmetric centers. Have you generated a new molecule?

Textbook Question

For each of the following molecules, identify all stereocenters and draw all possible stereoisomers.

(e)

Textbook Question

Tetracycline is called a broad-spectrum antibiotic because it is active against a wide variety of bacteria. How many asymmetric centers does tetracycline have?

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