Textbook Question
Rank the following carbocations in each set from most stable to least stable:
b.
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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 6a,b
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 6a,bChapter 7, Problem 6a,b
To which compound is the addition of HBr more highly regioselective?
a. 
b. 
Verified step by step guidance1
Step 1: Understand the concept of regioselectivity in addition reactions. Regioselectivity refers to the preference for the formation of one constitutional isomer over another in a chemical reaction. In the case of HBr addition to alkenes, the Markovnikov rule applies, which states that the hydrogen atom from HBr will add to the carbon with more hydrogen atoms (less substituted), and the bromine atom will add to the carbon with fewer hydrogen atoms (more substituted).
Step 2: Analyze the first pair of compounds (CH3CH2C=CH2 vs CH3C=CHCH3). In CH3CH2C=CH2, the double bond is terminal, meaning one of the carbons in the double bond is bonded to only one other carbon atom. In CH3C=CHCH3, the double bond is internal, meaning both carbons in the double bond are bonded to other carbon atoms. Terminal alkenes generally exhibit higher regioselectivity because the difference in substitution between the two carbons in the double bond is more pronounced.
Step 3: Analyze the second pair of compounds (cyclohexene with CH2 vs cyclohexene with CH3). In the first compound, the double bond is terminal, with one carbon bonded to only one other carbon atom. In the second compound, the double bond is internal, with both carbons bonded to other carbon atoms. Similar to the first pair, terminal alkenes tend to show higher regioselectivity due to the greater difference in substitution between the two carbons in the double bond.
Step 4: Compare the regioselectivity of HBr addition to the compounds in each pair. For both pairs, the terminal alkenes (CH3CH2C=CH2 and cyclohexene with CH2) are expected to exhibit higher regioselectivity because the Markovnikov addition of HBr is more pronounced when there is a clear difference in substitution between the two carbons in the double bond.
Step 5: Conclude that the addition of HBr is more highly regioselective to the terminal alkenes in both pairs of compounds. This is due to the greater difference in substitution between the carbons in the double bond, which makes the Markovnikov rule more applicable.
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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 occur at one location over another in a molecule. In the context of electrophilic addition reactions, such as the addition of HBr to alkenes, regioselectivity determines which carbon atom of the double bond will bond with the bromine atom and which will bond with the hydrogen atom, leading to different products.
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Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX (where X is a halogen) to an 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, as it indicates the regioselectivity based on the stability of the carbocation intermediates formed during the reaction.
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Carbocation Stability
Carbocation stability is a key factor in determining the outcome of electrophilic addition reactions. More stable carbocations, such as tertiary carbocations, are favored during the reaction process. The stability is influenced by factors such as the degree of substitution and resonance, which can affect the regioselectivity of the addition of HBr to alkenes.
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Related Practice
Textbook Question
What alkene should be used to synthesize each of the following alkyl bromides?
b.
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Textbook Question
What is the major product obtained from the addition of HBr to each of the following compounds?
e.
f.
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Textbook Question
Rank the following carbocations in each set from most stable to least stable:
a.
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Textbook Question
What is the major product obtained from the addition of HBr to each of the following compounds?
a.
b.
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Textbook Question
Is the structure of the transition state in the following reaction coordinate diagrams more similar to the structure of the reactant or to the structure of the product?
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