Textbook Question
How many stereoisomers are possible for the following alkenes?
(b)
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Ch. 8 - Alkenes I: Properties and Electrophilic Additions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 8 - Alkenes I: Properties and Electrophilic AdditionsProblem 62b
Mullins 1st EditionCh. 8 - Alkenes I: Properties and Electrophilic AdditionsProblem 62bChapter 7, Problem 62b
Which of the following alkenes would you expect to react fastest with HBr in each pair?
(b) 
Verified step by step guidance1
Identify the alkenes in the pair: The first alkene is 2-methyl-2-butene, and the second alkene is ethene (H₂C=CH₂).
Understand the mechanism of the reaction: The reaction of alkenes with HBr is an electrophilic addition reaction where the alkene's π bond attacks the electrophile (H⁺ from HBr), forming a carbocation intermediate.
Consider the stability of the carbocation intermediate: More substituted carbocations are more stable due to hyperconjugation and inductive effects. Tertiary carbocations are more stable than secondary, which are more stable than primary.
Analyze the structure of each alkene: 2-methyl-2-butene can form a tertiary carbocation upon reaction with HBr, while ethene can only form a primary carbocation.
Predict the reactivity: Since 2-methyl-2-butene forms a more stable tertiary carbocation, it will react faster with HBr compared to ethene, which forms a less stable primary carbocation.
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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. In the case of alkenes reacting with HBr, the double bond acts as a nucleophile, attacking the electrophilic hydrogen atom of HBr. This process leads to the formation of a carbocation intermediate, which is crucial for determining the reaction rate and product distribution.
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Carbocation Stability
Carbocation stability is a key factor influencing the rate of reaction in electrophilic addition. Carbocations can be classified based on their stability: tertiary > secondary > primary. The more stable the carbocation formed during the reaction, the faster the reaction will proceed. Therefore, when comparing alkenes, the one that can form a more stable carbocation will react more quickly with HBr.
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Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX (like HBr) 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 and is closely related to carbocation stability. Understanding this rule is essential for determining which alkene will react faster, as it guides the formation of the more stable carbocation.
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Related Practice
Textbook Question
Cyclooctene is one of the smaller rings that can form a trans alkene. Would you expect cis-cyclooctene or trans-cyclooctene to react more quickly in an acid-catalyzed hydration reaction?
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Textbook Question
Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (vi) 1. BH3 2. H2O2, NaOH
(k)
1287
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Textbook Question
Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (iv) H2SO4 , H2O
(k)
1294
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Textbook Question
Which of the following cycloalkanes would you expect to produce the least heat upon combustion when measured per CH2? Explain your answer.
203
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Textbook Question
Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr
(k)
1274
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