Textbook Question
Would you expect but-2-ene or 2-methylbut-2-ene to react more quickly with HBr?
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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 35b
Mullins 1st EditionCh. 8 - Alkenes I: Properties and Electrophilic AdditionsProblem 35bChapter 7, Problem 35b
Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H2O2
(b) 
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Identify the structure of the alkene involved in the reaction. Alkenes are hydrocarbons with a carbon-carbon double bond, which is the site of reactivity in these reactions.
For the reaction with HBr alone, apply Markovnikov's rule. This 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, and the halogen will attach to the carbon with fewer hydrogen atoms. This results in the formation of the more stable carbocation intermediate.
Draw the intermediate carbocation formed after the initial addition of HBr to the alkene. Consider the stability of the carbocation, as tertiary carbocations are more stable than secondary, which are more stable than primary.
For the reaction with HBr and H₂O₂, apply anti-Markovnikov's rule. In the presence of peroxides, the addition of HBr to an alkene proceeds via a radical mechanism, where the bromine atom attaches to the carbon with more hydrogen atoms, opposite to Markovnikov's rule.
Draw the expected product for each reaction, considering the regioselectivity (Markovnikov vs. anti-Markovnikov) and the mechanism (ionic vs. radical) involved in each case.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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 more hydrogen atoms, and the halogen will attach to the carbon with fewer hydrogen atoms. This rule helps predict the major product in the absence of peroxides.
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03:54
The 18 and 16 Electron Rule
Anti-Markovnikov Addition
Anti-Markovnikov addition occurs when HBr is added to an alkene in the presence of peroxides (H₂O₂). The reaction proceeds via a radical mechanism, resulting in the bromine atom attaching to the less substituted carbon, opposite to Markovnikov's Rule, due to the influence of the radical initiator.
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02:43Anti-Markovnikov addition of alcohols to terminal alkynes yields aldehydes
Radical Mechanism
A radical mechanism involves the formation of free radicals, which are highly reactive species with unpaired electrons. In the presence of peroxides, the addition of HBr to alkenes follows a radical pathway, leading to anti-Markovnikov products. Understanding this mechanism is crucial for predicting product formation in peroxide-mediated reactions.
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03:28The mechanism of Radical Polymerization.
Related Practice
Textbook Question
Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H2O2.
(e)
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Textbook Question
In your own words, explain why it is not possible to make primary alkyl halides, such as 1-bromopentane, using the electrophilic addition of HCl or HBr to an alkene.
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Textbook Question
Provide an arrow-pushing mechanism that rationalizes the formation of each of the products you predicted in Assessment 8.31. Make sure your mechanism accounts for all products formed, including stereoisomers and regioisomers, where applicable.
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Textbook Question
Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H2O2
(c)
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Textbook Question
Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H2O2.
(d)
1
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