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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Problem 7c

Textbook Question

We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(c)

Verified step by step guidance

Step 1: Identify the type of pericyclic reaction involved. Based on the reactants and products, this appears to be a hydroboration reaction, which is a type of concerted addition reaction where boron adds to the less substituted carbon of an alkene.

Step 2: Analyze the reactants. The alkene (CH2=CH-CH2CH3) is the electron-rich species, and the borane (BH3) is the electron-deficient species. The reaction proceeds via a cyclic transition state.

Step 3: Draw the mechanism. In the hydroboration step, the π-electrons of the alkene interact with the empty p-orbital of boron, while one of the B-H bonds simultaneously donates a proton to the more substituted carbon. This results in syn addition of boron and hydrogen across the double bond.

Step 4: Show the product formation. The boron atom attaches to the less substituted carbon (CH2 group), and the hydrogen attaches to the more substituted carbon (CH group). This regioselectivity is due to steric and electronic factors.

Step 5: Review the stereochemistry. The addition of boron and hydrogen occurs in a syn fashion, meaning both groups are added to the same face of the alkene. This stereochemical outcome is consistent with the concerted nature of the reaction.

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Key Concepts

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

Pericyclic Reactions

Pericyclic reactions are a class of organic reactions that occur through a concerted mechanism, involving a cyclic transition state. These reactions often involve the rearrangement of electrons in a way that conserves orbital symmetry, allowing for the formation of new bonds without the need for intermediates. Common types include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements.

Hydroboration

Hydroboration is a chemical reaction that involves the addition of borane (BH3) to alkenes, resulting in the formation of organoboranes. This reaction proceeds via a concerted mechanism, where the boron atom adds to the less substituted carbon of the alkene, leading to syn-addition. Hydroboration is often followed by oxidation to yield alcohols, making it a valuable method for synthesizing alcohols from alkenes.

Mechanism of Reactions

The mechanism of a chemical reaction describes the step-by-step process by which reactants are converted into products. It includes details about bond breaking and forming, the movement of electrons, and the role of intermediates. Understanding the mechanism is crucial for predicting the outcome of reactions, optimizing conditions, and designing new synthetic pathways in organic chemistry.

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Related Practice

Textbook Question

a. Starting with 3-methyl-1-butyne, how can you prepare the following alcohols?

1. 2-methyl-2-butanol

b. In each case, a second alcohol would also be obtained. What alcohol would it be?

Textbook Question

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

a. cyclohexene

b. 1-ethylcyclohexene

Textbook Question

Explain why 3-methylcyclohexene should not be used as the starting material in Problem 52b.

Textbook Question

How can the following compounds be synthesized, starting with a hydrocarbon that has the same number of carbons as the desired product?

b. CH₃CH₂CH₂CH₂OH

Textbook Question

What reagents are needed to synthesize the following alcohols?

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.

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We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.(c)

Key Concepts

Pericyclic Reactions

Hydroboration

Mechanism of Reactions

Watch next

We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(c)