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
Chapter 7, Problem 29
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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Identify the structures of DPP (Dimethylallyl pyrophosphate) and IPP (Isopentenyl pyrophosphate). Both are isomers and intermediates in the mevalonate pathway. DPP has a double bond at the terminal position, while IPP has a double bond in the internal position.
Recognize that the reaction is acid-catalyzed. This means a proton (H⁺) will be added to initiate the reaction. The acid catalyst will protonate the terminal double bond of DPP, forming a carbocation intermediate.
Draw the carbocation intermediate. Protonation of the double bond in DPP will result in a more stable secondary carbocation due to hyperconjugation and inductive effects.
Show the rearrangement of the carbocation. A 1,2-hydride shift occurs, where a hydrogen atom from the adjacent carbon migrates to stabilize the carbocation, forming a new carbocation at a different position.
Deprotonate the carbocation to regenerate the double bond in a new position, resulting in the formation of IPP. Verify the mechanism by ensuring that all steps follow the principles of stability (e.g., carbocation stability) and that the final product matches the structure of IPP.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Catalyzed Reactions
Acid-catalyzed reactions involve the use of an acid to increase the rate of a chemical reaction. In organic chemistry, acids can donate protons (H+) to substrates, facilitating the formation of reactive intermediates. Understanding how acids interact with molecules is crucial for predicting the pathway and products of the reaction, such as the conversion of DPP to IPP.
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Reaction Mechanism
A reaction mechanism is a step-by-step description of the process by which reactants are converted into products. It outlines the sequence of bond-breaking and bond-forming events, including the formation of intermediates. Drawing a mechanism helps visualize the transformation of DPP to IPP, allowing chemists to understand the roles of various species and the overall energy changes involved.
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Verification of Mechanisms
Verifying a reaction mechanism involves checking its consistency with experimental data and established chemical principles. This can include analyzing reaction rates, intermediates, and product distributions. A correct mechanism should align with known reactivity patterns and provide a plausible explanation for the observed outcomes, ensuring that the proposed steps are feasible under the given conditions.
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Related Practice
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
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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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
Which would you expect to be more selective for carbocation formation, the electrophilic addition of HF or HBr to 2-methylbut-2-ene? Explain your answer.
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