Textbook Question
Imagine an electrophilic addition where the first step is exothermic. Which carbocation—2°, 3°, or neither—would you expect to form preferentially? Explain.
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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 31d
Mullins 1st EditionCh. 8 - Alkenes I: Properties and Electrophilic AdditionsProblem 31dChapter 7, Problem 31d
What is the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HCl?
(d)
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Identify the structure of the alkene in part (d). Alkenes are hydrocarbons with a carbon-carbon double bond, which is the site of reactivity in addition reactions.
Understand the mechanism of electrophilic addition of HX (where X is a halogen, such as Br or Cl) to alkenes. The reaction proceeds via the formation of a carbocation intermediate.
For the reaction with HBr, the alkene will react with HBr to form a carbocation. The hydrogen from HBr will add to the less substituted carbon of the double bond, following Markovnikov's rule, which states that the more stable carbocation is formed.
Once the carbocation is formed, the bromide ion (Br-) will attack the positively charged carbon, resulting in the formation of the alkyl bromide product.
Repeat the process for the reaction with HCl. The mechanism is similar, where the chloride ion (Cl-) will attack the carbocation formed after the addition of HCl, resulting in the formation of the alkyl chloride product.
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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 the greater number of hydrogen atoms, while the halogen will attach to the carbon with fewer hydrogen atoms. This rule helps predict the major product in electrophilic addition reactions.
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The 18 and 16 Electron Rule
Electrophilic Addition Reaction
Electrophilic addition is a reaction where an electrophile reacts with an alkene, resulting in the addition of atoms across the double bond. The alkene's π electrons attack the electrophile, forming a carbocation intermediate, which is then attacked by a nucleophile, leading to the final product.
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Carbocation Stability
Carbocation stability is crucial in determining the major product of an electrophilic addition reaction. Tertiary carbocations are more stable than secondary, which are more stable than primary. The stability is influenced by hyperconjugation and the inductive effect, guiding the formation of the most stable intermediate during the reaction.
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Related Practice
Textbook Question
Would you expect but-2-ene or 2-methylbut-2-ene to react more quickly with HBr?
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Textbook Question
What is the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HCl?
(e)
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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
For the enzyme isopentenyl pyrophosphate isomerase, IPP binds tightly as a result of interactions between the active site amino acid residues and the diphosphate of IPP. Without concerning yourself with the structure of amino acids, what charges might you expect to be present in the active site to hold IPP in place so that the enzymatic reactions can occur?
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Textbook Question
Draw a mechanism for the acid-catalyzed conversion of DPP to IPP. How do you know that your mechanism is correct?
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