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

10. Addition Reactions

Hydroboration

Organic Chemistry

10. Addition Reactions

Hydroboration

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7:17 minutes

Problem 42c

Textbook Question

What stereoisomers are obtained from hydroboration–oxidation of the following compounds? Assign an R or S configuration to each asymmetric center.
c. cis-2-butene

Verified step by step guidance

Identify the reaction: Hydroboration–oxidation is a two-step reaction. The first step involves the addition of borane (BH₃) to the alkene, and the second step involves oxidation with hydrogen peroxide (H₂O₂) in a basic medium (NaOH). This reaction proceeds via anti-Markovnikov addition, where the hydroxyl group (-OH) attaches to the less substituted carbon of the double bond.

Analyze the starting material: cis-2-butene is a symmetrical alkene with the double bond between carbons 2 and 3. The two methyl groups are on the same side of the double bond, making it a cis isomer.

Determine the stereochemistry of the product: Hydroboration–oxidation occurs with syn addition, meaning that both the hydrogen (H) and hydroxyl group (-OH) are added to the same face of the double bond. This syn addition will result in the formation of a pair of enantiomers (stereoisomers) because the starting material is symmetrical.

Assign R or S configuration: After the addition of -OH and H, the product will have two chiral centers (at carbons 2 and 3). To assign R or S configuration, prioritize the substituents on each chiral center based on the Cahn-Ingold-Prelog rules. Assign priorities to the groups attached to each chiral center, determine the direction of rotation (clockwise or counterclockwise), and assign R (clockwise) or S (counterclockwise) accordingly.

Conclude the stereoisomers: The reaction will yield a racemic mixture of two enantiomers, one with (2R,3R) configuration and the other with (2S,3S) configuration, due to the symmetrical nature of the starting material and the syn addition mechanism.

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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. In organic chemistry, stereoisomers include enantiomers and diastereomers, which are crucial for understanding reactions involving chiral centers.

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction process used to convert alkenes into alcohols. In the first step, borane (BH3) adds across the double bond of the alkene, resulting in a trialkylborane intermediate. The second step involves oxidation with hydrogen peroxide (H2O2) in a basic solution, leading to the formation of an alcohol. This reaction is stereospecific and results in anti-Markovnikov addition.

R and S Configuration

The R and S configuration system is used to describe the absolute configuration of chiral centers in molecules. To assign R or S, the substituents attached to the chiral carbon are ranked according to their atomic number. The configuration is determined by the orientation of the highest priority substituent: if it is clockwise, the configuration is R; if counterclockwise, it is S. This is essential for understanding the stereochemistry of the products formed in reactions.

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Textbook Question

Draw the products, including their configurations, obtained from the reaction of 1-ethylcyclohexene with the following reagents:

c. R₂BH/THF, followed by HO^–, H₂O₂, H₂O

Textbook Question

Show how each of the following compounds can be synthesized from an alkene:

Textbook Question

Draw the product or products that will be obtained from the reaction of cis-2-butene and trans-2-butene with each of the following reagents. If a product can exist as stereoisomers, show which stereoisomers are formed.

2. BH₃/THF, followed by HO^-, H₂O₂, H₂O

Textbook Question

What stereoisomers are obtained from hydroboration–oxidation of the following compounds? Assign an R or S configuration to each asymmetric center.

d. (Z)-3,4-dimethyl-3-hexene

Textbook Question

Which is more highly regioselective: reaction of an alkene with BH₃ or with 9-BBN?

Textbook Question

Predict the major products of the following reactions, and give the structures of any intermediates. Include stereochemistry where appropriate.

(c)

Textbook Question

When (E)-3-methylhex-3-ene undergoes hydroboration–oxidation, two isomeric products are formed. Give their structures, and label each asymmetric carbon atom as (R) or (S). What is the relationship between these isomers? What is the relationship between the products formed from (Z)-3-methylhex-3-ene and those formed from (E)-3-methylhex-3-ene?

Textbook Question

Predict the major products of the following reactions. Include stereochemistry where applicable.

(c)

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