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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1:33 minutes

Problem 55c

Textbook Question

Suggest an alkene to undergo hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.
(c)

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Analyze the product structure: The alcohol group (-OH) is attached to a carbon that is stereochemically defined (wedge bond indicates stereochemistry). This suggests that the reaction involves stereospecificity.

Recall the mechanism of hydroboration–oxidation: This reaction adds water across the double bond of an alkene in an anti-Markovnikov fashion, meaning the -OH group will attach to the less substituted carbon. Additionally, the reaction proceeds with syn addition, meaning both the hydrogen and hydroxyl group are added to the same face of the alkene.

Determine the alkene structure: To achieve the observed stereochemistry, the starting alkene must have a double bond positioned such that the less substituted carbon becomes the site of hydroxyl group attachment. The stereochemistry of the product suggests that the alkene must have a cis configuration to allow syn addition.

Propose the alkene: Based on the product structure, the alkene should have a phenyl group (Ph) and an ethyl group on one side of the double bond, and a methyl group on the other side. The double bond should be positioned between the carbon bearing the phenyl group and the carbon bearing the methyl group.

Verify stereochemical outcome: Ensure that the proposed alkene, when undergoing hydroboration–oxidation, will lead to the observed stereochemistry of the alcohol product. The syn addition mechanism ensures that the hydrogen and hydroxyl group are added to the same face, resulting in the correct relative stereochemistry.

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Key Concepts

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

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction that converts 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) and a base (NaOH), which replaces the boron with a hydroxyl group, yielding an alcohol. This reaction is notable for its syn-addition mechanism, leading to specific stereochemical outcomes.

Stereochemistry

Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the context of hydroboration-oxidation, the stereochemical outcome is influenced by the syn-addition mechanism, which results in the formation of alcohols with specific stereochemical configurations. Understanding stereochemistry is crucial for predicting the relative configurations of products formed from reactions involving chiral centers.

Alkene Reactivity

Alkenes are reactive compounds due to the presence of a carbon-carbon double bond, which can undergo various addition reactions. The reactivity of alkenes in hydroboration-oxidation is influenced by factors such as sterics and electronic effects. When selecting an alkene for this reaction, it is essential to consider how substituents on the double bond will affect the regioselectivity and stereoselectivity of the resulting alcohol, particularly in the context of the desired product structure.

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Related Practice

Textbook Question

Predict the product(s) that would result when the following molecules are allowed to react under the following conditions: (i) 1. BH₃ 2. NaOH, H₂O₂. If there is no reaction, write 'no reaction.'

(a)

Textbook Question

a. Show the reagents required to form the primary alcohol in each of the following reactions.

Textbook Question

Identify A through O:

Textbook Question

Hydroboration, an electrophilic addition reaction like those studied in Section 21.4, only gives 1,2-addition to buta-1,3-diene, regardless of temperature. Why?

Textbook Question

Would you expect the following to produce an equal or unequal mixture of stereoisomers?

(c)

Textbook Question

Suggest an alkene to undergo hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.

(b)

Textbook Question

Suggest a reagent and a reactant that could be combined to make each of the following alcohols.

(a)

Textbook Question

Predict the products you would get when the following alkenes undergo (i) hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂ or (ii) oxymercuration–reduction [1. Hg(OAc)₂, H₂O 2. NaBH₄].

(a)

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Suggest an alkene to undergo hydroboration–oxidation (1. BH3 2. NaOH, H2O2) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.(c)

Key Concepts

Hydroboration-Oxidation

Stereochemistry

Alkene Reactivity

Watch next

Suggest an alkene to undergo hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.
(c)