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

Atropisomers

Organic Chemistry

5. Chirality

Atropisomers

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2:30 minutes

Problem 49c,d

Textbook Question

Which of the following compounds has a stereoisomer that is a meso compound?
c. 2,4-dimethylpentane
d. 1,3-dichlorocyclohexane

Verified step by step guidance

Step 1: Understand the concept of a meso compound. A meso compound is a molecule that has multiple stereocenters but is achiral due to an internal plane of symmetry. This symmetry makes the compound superimposable on its mirror image.

Step 2: Analyze the structure of 2,4-dimethylpentane. Draw the molecule and identify if it has stereocenters (carbon atoms bonded to four different groups). Check if the molecule has an internal plane of symmetry that would make it a meso compound.

Step 3: Analyze the structure of 1,3-dichlorocyclohexane. Draw the molecule in its chair conformation and identify the stereocenters (the carbons bonded to the chlorine atoms). Determine if the molecule has an internal plane of symmetry in any of its possible stereoisomeric forms.

Step 4: Compare the findings for both compounds. Determine which compound has a stereoisomer that meets the criteria for being a meso compound (multiple stereocenters and an internal plane of symmetry).

Step 5: Conclude which compound has a stereoisomer that is a meso compound based on the analysis. Remember that meso compounds are achiral despite having stereocenters.

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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. Stereoisomers can be further classified into enantiomers, which are non-superimposable mirror images, and diastereomers, which are not mirror images of each other.

Meso Compounds

Meso compounds are a specific type of stereoisomer that possess multiple chiral centers but are achiral due to an internal plane of symmetry. This means that despite having chiral centers, the overall molecule does not exhibit optical activity. Meso compounds can often be identified by their symmetrical structure, which allows for superimposition on their mirror image.

Chirality and Chiral Centers

Chirality is a property of a molecule that makes it non-superimposable on its mirror image, typically due to the presence of chiral centers, which are carbon atoms bonded to four different substituents. The presence of chiral centers in a molecule can lead to the formation of stereoisomers. Understanding chirality is crucial for identifying potential meso compounds, as the arrangement of substituents around chiral centers determines the molecule's stereochemical properties.

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Related Practice

Textbook Question

Which of the following compounds are meso?

(f)

Textbook Question

The original definition of meso is 'an achiral compound that has chiral diastereomers.' Our working definition of meso is 'an achiral compound that has chiral centers (usually asymmetric carbon atoms).' The working definition is much easier to apply, because we don't have to envision all possible chiral diastereomers of the compound. Still, the working definition is not quite as complete as the original definition.

a. Show how cis-cyclooctene is defined as a meso compound under the original definition, but not under our working definition. (Review Figure 5-19)

Textbook Question

Draw three-dimensional representations of the following compounds. Which have asymmetric carbon atoms? Which have no asymmetric carbons but are chiral anyway? Use your models for parts (a) through (d) and any others that seem unclear.

(g)

Textbook Question

A compound with two chiral centers that is meso will always have opposite absolute configurations at the two chiral centers. That is, a meso compound will never be (R,R) or (S,S); instead, it will be (R,S). Explain why this must be true.

Textbook Question

Which of the following compounds has a stereoisomer that is a meso compound?

a. 2,4-dibromohexane

b. 2,4-dibromopentane

Textbook Question

Which of the following has an achiral stereoisomer?

a. 2,3-dichlorobutane

b. 2,3-dichloropentane

Textbook Question

Which of the following compounds are chiral? Draw each compound in its most symmetric conformation, star (*) any asymmetric carbon atoms, and draw any mirror planes. Label any meso compounds. You may use Fischer projections if you prefer.

(d) (2R,3S)-2,3-dibromobutane

Textbook Question

Which of the following compounds are meso?

(e)

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