Textbook Question
What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction?
b.
1208
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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 Benzene
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. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 29
Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 29Chapter 9, Problem 29
Which of the double bonds in zingiberene, the compound responsible for the aroma of ginger, is most reactive in an electrophilic addition reaction with HBr?
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Identify the structure of zingiberene from the image. Zingiberene contains three double bonds labeled as 1, 2, and 3. These double bonds are located in different positions within the molecule, and their reactivity in electrophilic addition reactions depends on their electronic environment and steric factors.
Understand the mechanism of electrophilic addition of HBr. In this reaction, the π-electrons of the double bond attack the electrophilic hydrogen (H⁺) of HBr, forming a carbocation intermediate. The stability of this carbocation intermediate is a key factor in determining which double bond is most reactive.
Analyze the stability of the carbocation intermediates formed by each double bond. Double bond 1 forms a secondary carbocation, double bond 2 forms a tertiary carbocation, and double bond 3 forms a primary carbocation. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects, followed by secondary and then primary carbocations.
Consider steric hindrance and accessibility. Double bond 2 is located in a less sterically hindered position compared to double bond 1 and double bond 3, making it more accessible for the electrophilic addition reaction.
Conclude that double bond 2 is the most reactive in an electrophilic addition reaction with HBr because it forms the most stable carbocation (tertiary) and is in a relatively accessible position within the molecule.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition Reactions
Electrophilic addition reactions involve the addition of an electrophile to a nucleophile, typically across a double bond. In alkenes, the π bond is broken, allowing the electrophile to bond with one carbon atom while a nucleophile can bond with the other. The reactivity of the double bond is influenced by factors such as sterics and electronic effects, which determine how readily the double bond can react with electrophiles like HBr.
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Features of Addition Mechanisms.
Stability of Carbocation Intermediates
During electrophilic addition, a carbocation intermediate is often formed. The stability of this carbocation is crucial for determining the reactivity of the double bond. More stable carbocations, such as tertiary carbocations, are formed from more substituted double bonds, making those bonds more reactive in electrophilic addition reactions. Understanding the stability of these intermediates helps predict which double bond will react preferentially.
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Regioselectivity in Electrophilic Addition
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of electrophilic addition to alkenes, the Markovnikov rule often applies, stating that the more substituted carbon will bond with the electrophile. This concept is essential for predicting the outcome of the reaction with HBr in zingiberene, as it helps identify which double bond will be more reactive based on the structure of the compound.
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Related Practice
Textbook Question
What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction? Disregard stereoisomers.
b.
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What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction? Disregard stereoisomers.
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What products would be obtained from the reaction of 1,3,5-hexatriene with one equivalent of HBr? Disregard stereoisomers.
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What are the products of the following reactions, assuming that one equivalent of each reagent is used in each reaction?
c.
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What is the major product of each of the following reactions, assuming that one equivalent of each reagent is used in each reaction?
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