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

Fischer Projection

Organic Chemistry

5. Chirality

Fischer Projection

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2:42 minutes

Problem 4

Textbook Question

a. Are d-erythrose and l-erythrose enantiomers or diastereomers?
b. Are l-erythrose and l-threose enantiomers or diastereomers?

Verified step by step guidance

Step 1: Understand the definitions of enantiomers and diastereomers. Enantiomers are stereoisomers that are non-superimposable mirror images of each other, while diastereomers are stereoisomers that are not mirror images.

Step 2: Analyze the structures of d-erythrose and l-erythrose. These molecules are mirror images of each other, as the configuration of all chiral centers is opposite. This makes them enantiomers.

Step 3: Examine the structures of l-erythrose and l-threose. These molecules differ in the configuration of one or more (but not all) chiral centers, meaning they are not mirror images. This makes them diastereomers.

Step 4: Confirm the reasoning by comparing the Fischer projections of the molecules. For enantiomers, all chiral centers are inverted, while for diastereomers, only some chiral centers differ.

Step 5: Summarize the findings: d-erythrose and l-erythrose are enantiomers, while l-erythrose and l-threose are diastereomers.

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Key Concepts

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

Enantiomers

Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They typically arise in molecules with chiral centers, where the arrangement of atoms around the chiral carbon differs in such a way that one structure cannot be aligned with its mirror image. For example, D-erythrose and L-erythrose are enantiomers because they differ at all chiral centers.

Diastereomers

Diastereomers are stereoisomers that are not mirror images of each other. They occur when two or more chiral centers exist in a molecule, and at least one but not all of the chiral centers differ in configuration. In the case of L-erythrose and L-threose, they are diastereomers because they have different configurations at one of their chiral centers while sharing the same configuration at the other.

Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting carbohydrates and amino acids. In these projections, vertical lines represent bonds that go behind the plane of the page, while horizontal lines represent bonds that come out of the plane. This format helps in visualizing stereochemistry and determining relationships between different sugars, such as identifying enantiomers and diastereomers.

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Related Practice

Textbook Question

(a) There is only one ketotriose, called dihydroxyacetone. Draw its structure.

(b) There is only one aldotriose, called glyceraldehyde. Draw the two enantiomers of glyceraldehyde.

Textbook Question

For each set of examples, make a model of the first structure, and indicate the relationship of each of the other structures to the first structure. Examples of relationships: same compound, enantiomer, structural isomer.

(c)

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.

(e) (R,R)-2,3-dibromobutane

(f)

Textbook Question

Draw a Fischer projection for each compound. Remember that the cross represents an asymmetric carbon atom, and the carbon chain should be along the vertical, with the IUPAC numbering from top to bottom.

(e)

Textbook Question

For each pair, give the relationship between the two compounds. Making models will be helpful.

(e)

(f)

Textbook Question

For each structure,

1. draw all the stereoisomers.

2. label each structure as chiral or achiral.

3. give the relationships between the stereoisomers (enantiomers, diastereomers).

(a)

Textbook Question

Give the stereochemical relationships between each pair of structures. Examples are same compound, structural isomers, enantiomers, and diastereomers. Which pairs could you (theoretically) separate by distillation or recrystallization?

(a)

(b)

Textbook Question

Are the following pairs identical, enantiomers, diastereomers, or constitutional isomers?

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