Textbook Question
In this, and previous, chapters, we have seen 1,2-alkyl and 1,2-hydride shifts. If both are possible, as in the carbocation shown, which would you expect to occur? Explain your answer.
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Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes
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. 12 - Substitution and Elimination: Reactions of HaloalkanesProblem 73c
Mullins 1st EditionCh. 12 - Substitution and Elimination: Reactions of HaloalkanesProblem 73cChapter 11, Problem 73c
Suggest a mechanism for the following reactions.
(c) Elimination:
Verified step by step guidance1
Step 1: Protonation of the alcohol group - The reaction begins with the alcohol group (-OH) being protonated by sulfuric acid (H₂SO₄). This converts the hydroxyl group into a better leaving group, forming water (H₂O). The protonation step can be represented as: .
Step 2: Formation of the carbocation - After protonation, the water molecule leaves, generating a carbocation intermediate. This step is crucial as it determines the stability of the intermediate. The carbocation formed is tertiary, which is highly stable due to hyperconjugation and inductive effects.
Step 3: Rearrangement (if necessary) - In some cases, carbocation rearrangement may occur to form a more stable carbocation. However, in this reaction, the carbocation is already tertiary and stable, so no rearrangement is needed.
Step 4: Elimination of a proton - A base (often the bisulfate ion, HSO₄⁻, from sulfuric acid) abstracts a proton from a β-carbon adjacent to the carbocation. This leads to the formation of a double bond (alkene) via the E1 elimination mechanism. The most substituted alkene is formed due to Zaitsev's rule.
Step 5: Final product formation - The reaction concludes with the formation of the alkene product (2-methylcyclohexene) and water as a byproduct. The alkene is the major product due to its stability and adherence to Zaitsev's rule.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Elimination Reactions
Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond or a ring structure. In organic chemistry, these reactions often occur with the loss of a small molecule, such as water or hydrogen halide. The most common types are E1 and E2 mechanisms, which differ in their steps and conditions.
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Recognizing Elimination Reactions.
Acid-Catalyzed Dehydration
Acid-catalyzed dehydration is a specific type of elimination reaction where an alcohol is converted into an alkene through the removal of water. In this process, an acid, such as sulfuric acid (H2SO4), protonates the alcohol, making it a better leaving group. This leads to the formation of a carbocation intermediate, which can then lose a proton to form the double bond.
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Carbocation Stability
Carbocation stability is crucial in elimination reactions, as the stability of the carbocation intermediate influences the reaction pathway. Carbocations are classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the positively charged carbon. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects, making them more favorable in elimination mechanisms.
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Related Practice
Textbook Question
The bromoalkanes shown below participate in SN1 reactions with the relative rates shown. Explain this trend. relative rate:
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Textbook Question
Suggest a mechanism for the following reactions.
(b) Substitution :
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Textbook Question
Suggest a mechanism for the following reactions.
(a) Substitution:
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Textbook Question
Of the three possible elimination mechanisms (Figure 12.50), this chapter focused on two of them (E1 and E2). The third possibility occurs in situations like the one below. What makes this mechanism favored under these conditions?
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Textbook Question
Using pKₐ values, calculate Keq for the following acid–base reaction.
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