Textbook Question
Which is more highly regioselective: reaction of an alkene with BH3 or with 9-BBN?
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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 20
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 20Chapter 7, Problem 20
What will be the product of the preceding reaction if HBr is used in place of Br2?
Verified step by step guidance1
Step 1: Identify the type of reaction taking place. When HBr is used, it typically undergoes an electrophilic addition reaction with alkenes or alkynes, or a substitution reaction with alcohols or other functional groups. Determine the functional group present in the starting material.
Step 2: Analyze the mechanism of the reaction. If the starting material contains a double bond (alkene), HBr will add across the double bond following Markovnikov's rule, where the hydrogen atom attaches to the carbon with more hydrogens, and the bromine atom attaches to the carbon with fewer hydrogens.
Step 3: Consider the possibility of carbocation rearrangement. If the intermediate carbocation formed during the reaction can rearrange to a more stable carbocation (e.g., tertiary carbocation), this rearrangement will occur before bromine attaches.
Step 4: Write the structure of the product. After the bromine atom attaches to the appropriate carbon, the final product will be a bromoalkane. Ensure the stereochemistry is considered if applicable.
Step 5: Verify the reaction conditions. Confirm that no other reagents or conditions (e.g., peroxides) are present, as these could alter the mechanism (e.g., anti-Markovnikov addition in the presence of peroxides).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition
Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes or alkynes. In this context, HBr acts as the electrophile, adding across the double bond of an alkene. This process results in the formation of a more stable product, often a bromoalkane, depending on the structure of the starting material.
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1,2 vs 1,4 Addition
Markovnikov's Rule
Markovnikov's Rule states that when HX (where X is a halogen) adds to an unsymmetrical alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This rule helps predict the major product of the reaction when HBr is used, leading to the formation of the more stable carbocation intermediate and ultimately the more substituted alkyl halide.
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Carbocation Stability
Carbocation stability is a key concept in organic chemistry that refers to the relative stability of positively charged carbon species. Carbocations are stabilized by alkyl groups through hyperconjugation and inductive effects. In the context of the reaction with HBr, the formation of a more stable carbocation intermediate influences the final product, as the reaction pathway will favor the formation of the more substituted and stable carbocation.
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Related Practice
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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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
To understand why Br− adds to a carbon of the bromonium ion rather than to the positively charged bromine, draw the product that would be obtained if Br− did add to bromine.
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Textbook Question
Why are Na+ and K+ unable to form covalent bonds?
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