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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1:40 minutes

Problem 79a

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.

Verified step by step guidance

Step 1: Analyze the reaction mechanism. The hydroboration reaction involves the addition of 9-BBN (a bulky borane) to the alkene. Due to steric hindrance, 9-BBN selectively adds to the less hindered carbon of the double bond, forming a trialkylborane intermediate.

Step 2: Identify the regioselectivity. The image indicates that 9-BBN adds to the less hindered carbon with 99.3% regioselectivity. This means the boron atom attaches to the less substituted carbon of the double bond, while the hydrogen attaches to the more substituted carbon.

Step 3: Understand the oxidation step. The trialkylborane intermediate is oxidized using hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH). This oxidation converts the boron-carbon bond into a hydroxyl group (-OH), resulting in the formation of alcohols.

Step 4: Predict the products. The regioselectivity of the hydroboration step determines the position of the hydroxyl group in the final products. The major product will have the hydroxyl group on the less substituted carbon, while the minor product (if any) will have the hydroxyl group on the more substituted carbon.

Step 5: Draw the two organic products. The major product will be the alcohol with the hydroxyl group on the less substituted carbon, and the minor product (if formed) will have the hydroxyl group on the more substituted carbon. Use the provided structure to visualize the placement of the hydroxyl groups.

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Key Concepts

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

Hydroboration

Hydroboration is a chemical reaction that involves the addition of borane (BH3) or its derivatives to alkenes, resulting in the formation of trialkylboranes. This reaction proceeds via a concerted mechanism, where the boron atom adds to the less hindered carbon of the double bond, leading to regioselectivity. The use of bulky boranes like 9-BBN enhances this selectivity, allowing for the preferential formation of specific isomers.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of hydroboration, 9-BBN demonstrates high regioselectivity (99.3%) by adding to the less sterically hindered carbon of the alkene. This property is crucial for synthesizing specific products in organic reactions, influencing the overall yield and purity of the desired compound.

Oxidation of Trialkylboranes

The oxidation of trialkylboranes, such as those formed from hydroboration, typically involves treatment with hydrogen peroxide (H2O2) and sodium hydroxide (NaOH). This reaction converts the boron-containing compound into alcohols, effectively replacing the boron atom with a hydroxyl group. The outcome is the formation of alcohols that correspond to the original alkene's regioselectivity, thus providing insight into the reaction's mechanism and product distribution.

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Related Practice

Textbook Question

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

(c)

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?

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

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

(m)

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.

b. 9-BBN is synthesized by adding BH₃ across a symmetric, cyclic diene. What is the structure of the diene?

Textbook Question

Show how you would accomplish the following synthetic conversions.

(b) but-1-ene → butan-2-ol

Textbook Question

Show how you would synthesize the following alcohol from appropriate alkene.

(b)

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