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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15:06 minutes

Problem 14a

Textbook Question

When (Z)-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?

Verified step by step guidance

Step 1: Understand the reaction mechanism. Hydroboration–oxidation is a two-step reaction where an alkene reacts with borane (BH₃) in the first step, followed by oxidation with hydrogen peroxide (H₂O₂) and hydroxide (OH⁻). This reaction adds water (H and OH) across the double bond in a syn addition manner, meaning both groups are added to the same face of the alkene.

Step 2: Analyze the starting material. The compound (Z)-3-methylhex-3-ene is a stereoisomer with the double bond in the Z configuration, meaning the higher-priority groups on either side of the double bond are on the same side. This geometry will influence the stereochemistry of the products.

Step 3: Predict the products. During hydroboration–oxidation, the OH group is added to the less substituted carbon of the double bond (anti-Markovnikov addition), while the H is added to the more substituted carbon. Since the addition is syn, the stereochemistry of the products will depend on the orientation of the substituents in the starting material.

Step 4: Determine the stereochemistry of the products. After the addition, two stereoisomers are formed because the reaction creates a new chiral center at the carbons involved in the double bond. Label each asymmetric carbon atom in the products as (R) or (S) using the Cahn-Ingold-Prelog priority rules.

Step 5: Identify the relationship between the isomers. The two products are enantiomers, which are non-superimposable mirror images of each other. This is because the reaction creates two stereoisomers with opposite configurations at the chiral centers.

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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 process used to convert alkenes into alcohols. In the first step, borane (BH3) adds across the double bond of the alkene in a syn addition, leading to the formation of an organoborane intermediate. The second step involves oxidation with hydrogen peroxide (H2O2) in a basic solution, resulting in the formation of an alcohol. This reaction is notable for its anti-Markovnikov selectivity, meaning that the hydroxyl group ends up on the less substituted carbon.

Stereochemistry and Asymmetric Carbon

Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. An asymmetric carbon atom, or chiral center, is a carbon atom bonded to four different groups, leading to non-superimposable mirror images known as enantiomers. The configuration of these chiral centers is designated as (R) or (S) based on the Cahn-Ingold-Prelog priority rules, which help in determining the three-dimensional orientation of the substituents around the chiral center.

Isomerism

Isomerism is the phenomenon where two or more compounds have the same molecular formula but different structural or spatial arrangements of atoms. In the context of the hydroboration-oxidation of (Z)-3-methylhex-3-ene, the reaction produces two isomeric alcohols, which can differ in their stereochemistry due to the presence of chiral centers. These isomers can be classified as enantiomers if they are non-superimposable mirror images or diastereomers if they differ at one or more chiral centers but not all.

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Related Practice

Textbook Question

What is the major product obtained from hydroboration–oxidation of the following alkenes?

a. 2-methyl-2-butene

Textbook Question

Disiamylborane adds only once to alkynes by virtue of its two bulky secondary isoamyl groups. Disiamylborane is prepared by the reaction of BH₃·THF with an alkene.

a. Draw the structural formulas of the reagents and the products in the preparation of disiamylborane.

b. Explain why the reaction in part (a) goes only as far as the dialkylborane. Why is Sia₃B not formed?

Textbook Question

In the hydroboration of 1-methylcyclopentene shown in Solved Problem 8-3, the reagents are achiral, and the products are chiral. The product is a racemic mixture of trans-2-methylcyclopentanol, but only one enantiomer is shown. Show how the other enantiomer is formed.

Textbook Question

Show how you would synthesize each compound using methylenecyclohexane as your starting material.

(c)

Textbook Question

When 1,2-dimethylcyclopentene undergoes hydroboration–oxidation, one diastereomer of the product predominates. Show why this addition is stereospecific, and predict the stereochemistry of the major product.

Textbook Question

An inexperienced graduate student treated dec-5-ene with borane in THF, placed the flask in a refrigerator, and left for a party. When he returned from the party, he discovered that the refrigerator was broken and that it had gotten quite warm inside. Although all the THF had evaporated from the flask, he treated the residue with basic hydrogen peroxide. To his surprise, he recovered a fair yield of decan-1-ol. Use a mechanism to show how this reaction might have occurred. (Hint: The addition of BH₃ is reversible.)

Textbook Question

The bulky borane 9-BBN was developed to enhance the selectivity of hydroboration. In this example, 9-BBN adds to the less hindered carbon with 99.3% regioselectivity, compared with only 57% for diborane.

a. Show the two organic products generated when the trialkylborane is oxidized with H₂O₂/NaOH.

Textbook Question

Draw the organic products you would expect to isolate from the following reactions (after hydrolysis).

(m)

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When (Z)-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?

Key Concepts

Hydroboration-Oxidation

Stereochemistry and Asymmetric Carbon

Isomerism

Watch next

When (Z)-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?