Textbook Question
Show how you might synthesize the following compounds starting with bromobenzene, and alkyl or alkenyl halides of four carbon atoms or fewer.
a. 3-phenylprop-1-ene
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Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
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
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Wade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 12
Wade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 12Chapter 15, Problem 12
Addition of 1-bromobut-2-ene to magnesium metal in dry ether results in formation of a Grignard reagent. Addition of water to this Grignard reagent gives a mixture of but-1-ene and but-2-ene (cis and trans). When the Grignard reagent is made using 3-bromobut-1-ene, addition of water produces exactly the same mixture of products in the same ratios. Explain this curious result
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Identify the structure of the Grignard reagent formed from 1-bromobut-2-ene. The reaction of 1-bromobut-2-ene with magnesium in dry ether forms a Grignard reagent, which is an organomagnesium compound. The Grignard reagent will have the structure CH3CH=CHCH2MgBr.
Consider the reaction of the Grignard reagent with water. When water is added to the Grignard reagent, it acts as a proton donor, converting the organomagnesium compound into a hydrocarbon. The Grignard reagent CH3CH=CHCH2MgBr will react with water to form but-1-ene (CH3CH=CHCH2) and but-2-ene (CH3CH=CHCH3).
Analyze the formation of but-1-ene and but-2-ene. The Grignard reagent can undergo rearrangement or isomerization before reacting with water, leading to the formation of both but-1-ene and but-2-ene. This is due to the presence of a double bond, which allows for such rearrangements.
Examine the Grignard reagent formed from 3-bromobut-1-ene. The reaction of 3-bromobut-1-ene with magnesium in dry ether forms a Grignard reagent with the structure CH2=CHCH2CH2MgBr. This reagent can also undergo similar rearrangements or isomerizations.
Explain the identical product mixture. Both Grignard reagents, despite originating from different starting materials, can rearrange to form the same carbocation intermediates, leading to the same mixture of but-1-ene and but-2-ene upon reaction with water. This is why the product mixtures are identical in composition and ratio.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Grignard Reagent Formation
Grignard reagents are organomagnesium compounds formed by the reaction of an alkyl or aryl halide with magnesium metal in anhydrous ether. They are highly reactive and serve as nucleophiles in organic synthesis. In this context, 1-bromobut-2-ene reacts with magnesium to form a Grignard reagent, which is crucial for subsequent reactions.
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Carbonation of Grignard Reagents
Carbanion Stability and Rearrangement
Grignard reagents can form carbanions, which are negatively charged carbon species. These carbanions can undergo rearrangement to form more stable intermediates. In this case, the carbanion formed from the Grignard reagent can rearrange, leading to the same mixture of but-1-ene and but-2-ene, regardless of the starting alkene's position.
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Alkene Isomerization
Alkene isomerization involves the conversion of one alkene isomer to another, such as from cis to trans or from one positional isomer to another. This process can occur under certain conditions, such as the presence of a Grignard reagent, which can facilitate the rearrangement of double bonds, resulting in a mixture of but-1-ene and but-2-ene isomers.
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Related Practice
Textbook Question
Show how you might synthesize the following compounds starting with bromobenzene, and alkyl or alkenyl halides of four carbon atoms or fewer.
c. dec-5-ene
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Textbook Question
When Br2 is added to buta-1,3-diene at –15 °C, the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 60 °C, the product ratio is 10% A and 90% B.
a. Propose structures for products A and B. (Hint: In many cases, an allylic carbocation is more stable than a bromonium ion.)
b. Propose a mechanism to account for formation of both A and B.
c. Show why A predominates at –15 °C and B predominates at 60 °C.
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Textbook Question
When Br2 is added to buta-1,3-diene at –15 °C, the product mixture contains 60% of product A and 40% of product B. When the same reaction takes place at 60 °C, the product ratio is 10% A and 90% B.
d. If you had a solution of pure A, and its temperature were raised to 60 °C, what would you expect to happen? Propose a mechanism to support your prediction.
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Textbook Question
Show how you might synthesize the following compounds starting with bromobenzene, and alkyl or alkenyl halides of four carbon atoms or fewer.
b. 5-methylhex-2-ene
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Textbook Question
When N-bromosuccinimide is added to hex-1-ene in CCl4 and a sunlamp is shone on the mixture, three products result.
(a) Give the structures of these three products.
(b) Propose a mechanism that accounts for the formation of these three products
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