Textbook Question
Draw the important resonance contributors for the following cations, anions, and radicals.
(b)
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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 26b
Wade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 26bChapter 15, Problem 26b
Show how the reaction of an allylic halide with a Grignard reagent might be used to synthesize the following hydrocarbons.
b. 2,5,5-trimethylhept-2-ene
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Identify the structure of the target molecule, 2,5,5-trimethylhept-2-ene. This molecule contains a double bond at the second carbon and three methyl groups attached to the fifth carbon. Break the molecule into two fragments: one that will come from the allylic halide and the other from the Grignard reagent.
Determine the allylic halide fragment. Since the target molecule has a double bond at the second carbon, the allylic halide should have a halogen (e.g., bromine) attached to the carbon adjacent to the double bond. For this synthesis, use 3-bromo-2-methylpropene as the allylic halide.
Determine the Grignard reagent fragment. The Grignard reagent will contribute the remaining carbon chain. In this case, use tert-butylmagnesium bromide (t-BuMgBr) to introduce the 5,5-dimethyl group (tert-butyl group) to the molecule.
Write the reaction mechanism. The Grignard reagent (t-BuMgBr) will attack the allylic halide (3-bromo-2-methylpropene) at the allylic position, displacing the bromine atom and forming a new carbon-carbon bond. This reaction proceeds via an SN2' (allylic substitution) mechanism, where the nucleophile attacks the allylic position opposite the leaving group.
Verify the product structure. After the reaction, confirm that the resulting molecule matches the structure of 2,5,5-trimethylhept-2-ene, with the double bond at the second carbon and the tert-butyl group attached to the fifth carbon.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Allylic Halides
Allylic halides are organic compounds where a halogen atom is bonded to an allylic carbon, which is adjacent to a double bond. This positioning makes them reactive in nucleophilic substitution reactions, allowing for the formation of new carbon-carbon bonds when reacted with nucleophiles like Grignard reagents. Understanding the structure and reactivity of allylic halides is crucial for predicting the outcomes of synthetic reactions.
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Grignard Reagents
Grignard reagents are organomagnesium compounds represented as R-MgX, where R is an organic group and X is a halogen. They are powerful nucleophiles that can react with electrophiles to form new carbon-carbon bonds. In the context of synthesizing hydrocarbons, Grignard reagents can add to carbonyl compounds or react with allylic halides to create larger, more complex molecules.
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Stereochemistry and Regioselectivity
Stereochemistry and regioselectivity are essential concepts in organic synthesis that refer to the spatial arrangement of atoms in molecules and the preference for certain reaction pathways, respectively. When synthesizing compounds like 2,5,5-trimethylhept-2-ene, understanding how the reaction conditions influence the formation of specific isomers is vital. This knowledge helps predict the major products and their configurations resulting from the reaction of allylic halides with Grignard reagents.
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Related Practice
Textbook Question
Predict the products of the following reactions.
(h) cyclopentadiene + methyl acrylate, CH2=CH–COOCH3
2
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Textbook Question
Show how the reaction of an allylic halide with a Grignard reagent might be used to synthesize the following hydrocarbons.
c. 1-cyclopentylpent-2-ene
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Textbook Question
Show how the reaction of an allylic halide with a Grignard reagent might be used to synthesize the following hydrocarbons.
a. 5-methylhex-1-ene
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Textbook Question
Draw the important resonance contributors for the following cations, anions, and radicals.
(a)
3
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Textbook Question
Predict the products of the following reactions.
(i)
1
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