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

Enantiomers vs. Diastereomers

Organic Chemistry

5. Chirality

Enantiomers vs. Diastereomers

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3:17 minutes

Problem 36d,e,f

Textbook Question

Free-radical bromination of the following compound introduces bromine primarily at the benzylic position next to the aromatic ring. If the reaction stops at the monobromination stage, two stereoisomers result.

d. What is the relationship between the two isomeric products?
e. Will these two products be produced in identical amounts? That is, will the product mixture be exactly 50:50?
f. Will these two stereoisomers have identical physical properties such as boiling point, melting point, solubility, etc.? Could they be separated (theoretically, at least) by distillation or recrystallization?

Verified step by step guidance

Step 1: Analyze the reaction conditions. The reaction involves free-radical bromination using Br₂ and hv (light). This type of reaction typically occurs at the most stable radical position, which in this case is the benzylic position adjacent to the aromatic ring.

Step 2: Consider the stereochemistry of the benzylic position. The benzylic carbon is a stereocenter, meaning that bromination at this position can lead to two stereoisomers due to the formation of a new chiral center.

Step 3: Address part (d). The relationship between the two isomeric products is that they are enantiomers. Enantiomers are non-superimposable mirror images of each other, differing in the spatial arrangement of atoms around the chiral center.

Step 4: Address part (e). The two enantiomers will be produced in identical amounts (50:50) because the reaction does not favor one enantiomer over the other. This is due to the symmetrical nature of the radical intermediate formed during the reaction.

Step 5: Address part (f). Enantiomers have identical physical properties such as boiling point, melting point, and solubility in achiral environments. However, they can be separated theoretically by methods such as recrystallization using a chiral resolving agent or chromatography on a chiral stationary phase, but not by simple distillation.

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Key Concepts

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

Free-Radical Bromination

Free-radical bromination is a reaction mechanism where bromine (Br2) reacts with alkanes or substituted alkanes in the presence of light or heat, generating bromine radicals. These radicals abstract hydrogen atoms from the substrate, leading to the formation of alkyl radicals, which can then react with bromine to form bromoalkanes. This process is selective, often favoring the formation of products at more stable radical sites, such as benzylic positions adjacent to aromatic rings.

Stereoisomers

Stereoisomers are compounds that have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. In the context of bromination at the benzylic position, two stereoisomers can arise due to the presence of chiral centers created during the reaction. These isomers can exhibit different physical properties and reactivity, making their study important in organic chemistry.

Physical Properties of Stereoisomers

Stereoisomers can have different physical properties, such as boiling points, melting points, and solubility, due to their distinct spatial arrangements. For example, enantiomers (a type of stereoisomer) often have identical physical properties in achiral environments but can behave differently in chiral environments. This difference can affect separation techniques like distillation or recrystallization, where the isomers may not be produced in equal amounts, leading to potential challenges in isolating them.

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Related Practice

Textbook Question

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

(c)

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.

(i)

Textbook Question

For each of the compounds described by the following names,

1. draw a three-dimensional representation.

2. star (*) each chiral center.

3. draw any planes of symmetry.

4. draw any enantiomer.

5. draw any diastereomers.

6. label each structure you have drawn as chiral or achiral.

a. (S)-2-chlorobutane

b. (R)-1,1,2-trimethylcyclohexane

Textbook Question