Textbook Question
How does the first step in the reaction of propene with Br2 differ from the first step in the reaction of propene with HBr?
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Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 18
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 18Chapter 7, Problem 18
Which is more highly regioselective: reaction of an alkene with BH3 or with 9-BBN?
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Understand the concept of regioselectivity: Regioselectivity refers to the preference of a chemical reaction to produce one structural isomer over another when multiple outcomes are possible. In the context of hydroboration, regioselectivity determines which carbon in the alkene will bond to the boron atom.
Recall the hydroboration mechanism: In the hydroboration of an alkene, the boron atom adds to the less substituted carbon (anti-Markovnikov addition), while the hydrogen adds to the more substituted carbon. This is due to steric and electronic factors.
Compare BH3 and 9-BBN: BH3 (borane) is a smaller, less sterically hindered molecule, while 9-BBN (9-borabicyclo[3.3.1]nonane) is a bulky boron reagent. The bulkiness of 9-BBN increases its steric hindrance, making it more selective in targeting the less substituted carbon of the alkene.
Explain why 9-BBN is more regioselective: The increased steric hindrance of 9-BBN forces it to approach the alkene in a more controlled manner, favoring the addition to the less substituted carbon. This makes 9-BBN more highly regioselective compared to BH3.
Conclude the comparison: While both BH3 and 9-BBN follow the same anti-Markovnikov addition pattern, 9-BBN exhibits greater regioselectivity due to its bulkier structure, which limits alternative reaction pathways and enhances selectivity for the less substituted carbon.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple isomers are possible. In the context of alkene reactions, it indicates which carbon atom of the alkene is more likely to bond with a reagent, leading to the formation of a specific product. Understanding regioselectivity is crucial for predicting the outcome of reactions involving alkenes.
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Heck Reaction
Hydroboration
Hydroboration is a chemical reaction that involves the addition of borane (BH3) or its derivatives to alkenes, resulting in the formation of organoboranes. This reaction is characterized by its anti-Markovnikov selectivity, where the boron atom attaches to the less substituted carbon of the alkene. The regioselectivity of hydroboration is influenced by the sterics and electronics of the alkene and the boron reagent used.
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9-BBN
9-BBN (9-borabicyclo[3.3.1]nonane) is a bulky boron reagent used in hydroboration reactions. Its structure provides unique steric properties that enhance regioselectivity, often favoring the formation of less substituted products. When comparing 9-BBN to BH3, the bulkiness of 9-BBN typically leads to higher regioselectivity in reactions with alkenes, making it a valuable reagent in synthetic organic chemistry.
Related Practice
Textbook Question
What is the major product obtained from the reaction of HBr with each of the following?
a.
Textbook Question
What is the major product obtained from the reaction of HBr with each of the following?
b.
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Textbook Question
What is the major product obtained from hydroboration–oxidation of the following alkenes?
a. 2-methyl-2-butene
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Textbook Question
Which of the following carbocations would you expect to rearrange?
Textbook Question
What will be the product of the preceding reaction if HBr is used in place of Br2?
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