Textbook Question
Make models of the following compounds, and predict the products formed when they react with the strong bases shown.
(b) meso-1,2-dibromo-1,2-diphenylethane + (CH3CH2)3N:
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Ch. 7 - Structure and Synthesis of Alkenes; Elimination
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 7, Problem 28a
Predict the elimination products of the following reactions, and label the major products.
a. cis-1-bromo-2-methylcyclohexane + NaOCH3 in CH3OH
Verified step by step guidance1
Step 1: Identify the type of elimination reaction. This reaction involves NaOCH3 in CH3OH, which is a strong base and a polar protic solvent. This setup typically favors an E2 elimination mechanism.
Step 2: Analyze the structure of the substrate (cis-1-bromo-2-methylcyclohexane). In an E2 reaction, the β-hydrogen must be anti-periplanar to the leaving group (Br). Draw the chair conformation of the cyclohexane ring to determine the positions of the β-hydrogens relative to the bromine atom.
Step 3: Determine the possible β-hydrogens that can be eliminated. In cis-1-bromo-2-methylcyclohexane, there are β-hydrogens on the carbons adjacent to the carbon bonded to the bromine. Check which β-hydrogens are anti-periplanar to the bromine in the chair conformation.
Step 4: Predict the elimination products. The elimination of a β-hydrogen and the bromine atom will result in the formation of a double bond. Consider the regioselectivity (Zaitsev's rule) to predict the major product, which is the more substituted alkene.
Step 5: Label the major and minor products. Based on Zaitsev's rule, the major product will be the more substituted alkene, while the minor product will be the less substituted alkene. Draw the structures of both products and label them accordingly.
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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. In organic chemistry, these reactions can follow either E1 or E2 mechanisms, depending on the substrate and conditions. Understanding the mechanism is crucial for predicting the products, as it influences the stereochemistry and regioselectivity of the reaction.
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Stereochemistry
Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the case of cis-1-bromo-2-methylcyclohexane, the relative positions of substituents can lead to different elimination products. Recognizing the stereochemical configuration is essential for predicting which product will be favored in elimination reactions.
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Regioselectivity
Regioselectivity is the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In elimination reactions, the stability of the resulting alkene plays a significant role in determining the major product. For example, more substituted alkenes are generally more stable and thus favored in elimination reactions, guiding predictions about the major product.
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Related Practice
Textbook Question
Make models of the following compounds, and predict the products formed when they react with the strong bases shown.
(c) (d,l)-1,2-dibromo-1,2-diphenylethane + (CH3CH2)3N:
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Textbook Question
Make models of the following compounds, and predict the products formed when they react with the strong bases shown.
(d)
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Textbook Question
Two stereoisomers of a bromodecalin are shown. Although the difference between these stereoisomers may seem trivial, one isomer undergoes elimination with KOH much faster than the other. Predict the products of these eliminations, and explain the large difference in the ease of elimination.
Textbook Question
When the following stereoisomer of 2-bromo-1,3-dimethylcyclohexane is treated with sodium methoxide, no E2 reaction is observed. Explain why this compound cannot undergo the E2 reaction in the chair conformation.
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Textbook Question
Predict the elimination products of the following reactions, and label the major products.
b. trans-1-bromo-2-methylcyclohexane + NaOCH3 in CH3OH
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