Textbook Question
Show how you would accomplish the following synthetic conversions.
(a) but−1−ene → 1−bromobutane
(b) but−1−ene → 2−bromobutane
5
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Ch.8 - Reactions of Alkenes
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 8, Problem 5
Propose a mechanism to show how 3,3-dimethylbut-1-ene reacts with dilute aqueous H2SO4 to give 2,3-dimethylbutan-2-ol and a small amount of 2,3-dimethylbut-2-ene.
HINT: When predicting products for electrophilic additions, first draw the structure of the carbocation (or other intermediate) that results from electrophilic attack.
Verified step by step guidance1
Step 1: Begin by identifying the electrophilic addition reaction mechanism. The dilute aqueous H2SO4 provides H⁺ ions, which act as the electrophile. The π-electrons in the double bond of 3,3-dimethylbut-1-ene will attack the H⁺, leading to the formation of a carbocation intermediate.
Step 2: Determine the most stable carbocation intermediate. The double bond in 3,3-dimethylbut-1-ene is between the first and second carbon atoms. Protonation of the double bond can occur at either carbon, but the resulting carbocation will be more stable if formed at the second carbon due to hyperconjugation and inductive effects from the adjacent alkyl groups.
Step 3: Draw the structure of the carbocation intermediate. After protonation, the double bond is broken, and a positive charge is localized on the second carbon atom. This carbocation is stabilized by the two methyl groups attached to the second carbon, making it a tertiary carbocation.
Step 4: Consider the nucleophilic attack by water. The carbocation intermediate is highly reactive and will be attacked by a water molecule (H₂O), which acts as a nucleophile. This leads to the formation of a protonated alcohol intermediate.
Step 5: Deprotonation of the protonated alcohol intermediate occurs. A water molecule or another base in the solution will remove the extra proton from the oxygen atom, resulting in the formation of 2,3-dimethylbutan-2-ol as the major product. Additionally, a small amount of 2,3-dimethylbut-2-ene is formed via elimination of water from the carbocation intermediate.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition Mechanism
Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, typically involving alkenes. In this case, the double bond of 3,3-dimethylbut-1-ene acts as a nucleophile, attacking the electrophilic hydrogen from dilute aqueous H2SO4, leading to the formation of a carbocation intermediate.
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Features of Addition Mechanisms.
Carbocation Stability
Carbocations are positively charged intermediates that play a crucial role in many organic reactions. Their stability is influenced by the degree of substitution; tertiary carbocations are more stable than secondary or primary ones. In this reaction, the formation of a stable tertiary carbocation from 3,3-dimethylbut-1-ene is favored, which subsequently leads to the formation of the alcohol product.
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Markovnikov's Rule
Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the major product in this reaction, where the addition of H2SO4 to 3,3-dimethylbut-1-ene results in the formation of 2,3-dimethylbutan-2-ol as the main product, following the regioselectivity outlined by the rule.
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Related Practice
Textbook Question
Predict the products of the following hydration reactions.
b. 2-phenylpropene + dilute acid
c. 1-phenylcyclohexene + dilute acid
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Textbook Question
a. Propose a mechanism for the following reaction.
b. Give the structure of the product that results when this intermediate is reduced by sodium borohydride.
1
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Textbook Question
Predict the products of the following hydration reactions.
a. 1−methylcyclopentene + dilute acid
3
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Textbook Question
Show how you would accomplish the following synthetic conversions.
(c) 2−methylcyclohexanol → 1−bromo−1−methylcyclohexane
2
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Textbook Question
Show how you would accomplish the following synthetic conversions.
(d) 2−methylbutan-2-ol → 2-bromo-3-methylbutane
1
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