Textbook Question
Describe how each of the following compounds could be synthesized from the given starting material.
a.
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Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing CompoundsProblem 80
Bruice 8th EditionCh. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing CompoundsProblem 80Chapter 11, Problem 80
When the following seven-membered ring alcohol is dehydrated, three alkenes are formed. Propose a mechanism for their formation.
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Step 1: Recognize that the reaction involves acid-catalyzed dehydration of the alcohol. Sulfuric acid (H₂SO₄) acts as a catalyst, and heat (Δ) promotes the elimination of water to form alkenes.
Step 2: Protonation of the hydroxyl group occurs first. The alcohol group (-OH) is protonated by H₂SO₄, converting it into a better leaving group (water, H₂O). This step increases the electrophilicity of the carbon attached to the hydroxyl group.
Step 3: Formation of a carbocation intermediate. After the departure of water, a carbocation is formed at the carbon where the hydroxyl group was originally attached. The stability of this carbocation is influenced by hyperconjugation and alkyl substituents.
Step 4: Rearrangement of the carbocation. The seven-membered ring allows for possible hydride or alkyl shifts to form more stable carbocations. This rearrangement can lead to different carbocation intermediates, which will ultimately result in the formation of multiple alkenes.
Step 5: Elimination of a proton (E1 mechanism). A base (often the conjugate base of H₂SO₄) abstracts a proton from a β-carbon adjacent to the carbocation, leading to the formation of double bonds (alkenes). Depending on the position of the β-hydrogens, three different alkenes are formed as shown in the image.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Dehydration Reaction
Dehydration reactions involve the removal of a water molecule from a compound, often resulting in the formation of a double bond. In the context of alcohols, this process typically occurs under acidic conditions, where the hydroxyl group is protonated, making it a better leaving group. The elimination of water leads to the formation of alkenes, which can vary based on the structure of the starting material.
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Mechanism of Alkene Formation
The mechanism for alkene formation from alcohols generally follows an E1 or E2 pathway. In the E1 mechanism, the first step involves the formation of a carbocation after the leaving of water, followed by the elimination of a proton to form a double bond. In the E2 mechanism, the elimination occurs in a single concerted step, where a base abstracts a proton while the leaving group departs, leading to the formation of the alkene.
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Regioselectivity and Stereochemistry
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others. In the dehydration of the seven-membered ring alcohol, multiple alkenes can form due to different positions of double bond formation. Stereochemistry also plays a role, as the spatial arrangement of substituents around the double bond can lead to different geometric isomers, influencing the overall product distribution.
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Related Practice
Textbook Question
Propose a mechanism for each of the following reactions:
a.
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Textbook Question
When ethyl ether is heated with excess HI for several hours, the only organic product obtained is ethyl iodide. Explain why ethyl alcohol is not obtained as a product.
2
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Textbook Question
How could you synthesize isopropyl propyl ether, using isopropyl alcohol as the only carbon-containing reagent?
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Textbook Question
Propose a mechanism for each of the following reactions:
b.
1
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Textbook Question
Ethylene oxide reacts readily with HO- because of the strain in the three-membered ring. Explain why cyclopropane, a compound with approximately the same amount of strain, does not react with HO-.
1
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