Textbook Question
Write a balanced equation for each reaction, showing the major product you expect.
(b)
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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 55a,b,c
Predict the dehydrohalogenation product(s) that result when the following alkyl halides are heated in alcoholic KOH. When more than one product is formed, predict the major and minor products.
(a) 
(b) 
(c) 
Verified step by step guidance1
Step 1: Understand the reaction mechanism. Dehydrohalogenation involves the elimination of a hydrogen atom and a halogen atom (e.g., Br or Cl) from adjacent carbon atoms, forming a double bond. This reaction typically follows the E2 mechanism when heated in alcoholic KOH.
Step 2: Analyze the structure of the alkyl halide in part (a), (CH3)2CH-C(CH3)2Br. Identify the β-hydrogens (hydrogens on carbons adjacent to the carbon bonded to the halogen). The bulky tert-butyl group (C(CH3)2) limits steric accessibility, favoring elimination from the less hindered β-carbon.
Step 3: For part (b), (CH3)2CH-CH(CH3)Br, identify the β-hydrogens on the adjacent carbons. There are two possible β-carbons, leading to two possible alkenes. Apply Zaitsev's rule, which states that the more substituted alkene is typically the major product.
Step 4: For part (c), (CH3)2C(Br)CH2CH3, identify the β-hydrogens on the adjacent carbons. There are two β-carbons, leading to two possible elimination products. Again, apply Zaitsev's rule to predict the major product, which will be the more substituted alkene.
Step 5: Consider stereochemistry and regioselectivity for all parts. In cases where multiple β-hydrogens are available, the reaction may produce both E and Z isomers. The major product is typically the thermodynamically favored isomer (more stable configuration).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Dehydrohalogenation
Dehydrohalogenation is an elimination reaction where a hydrogen halide (HX) is removed from an alkyl halide, resulting in the formation of an alkene. This process typically occurs under basic conditions, such as with alcoholic KOH, which promotes the elimination of the halogen and a hydrogen atom from adjacent carbon atoms. The reaction can yield multiple products, including alkenes with different degrees of substitution.
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03:02
The dehydrohalogenation mechanism.
Zaitsev's Rule
Zaitsev's Rule states that in elimination reactions, the more substituted alkene is generally the major product. This is because more substituted alkenes are more stable due to hyperconjugation and the inductive effect. When predicting products, it is essential to consider the structure of the starting alkyl halide and the possible alkene products to determine which will be favored.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the context of dehydrohalogenation, regioselectivity is influenced by the stability of the resulting alkenes. Understanding the sterics and electronics of the alkyl halides involved helps predict which alkene will be the major or minor product in the reaction.
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Related Practice
Textbook Question
Write a balanced equation for each reaction, showing the major product you expect.
(d)
1657
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Textbook Question
Predict the dehydrohalogenation product(s) that result when the following alkyl halides are heated in alcoholic KOH. When more than one product is formed, predict the major and minor products.
(f)
1206
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Textbook Question
Using cyclohexane as your starting material, show how you would synthesize each of the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)
a. bromocyclohexane
b. cyclohexene
c. ethoxycyclohexane
1798
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Textbook Question
Predict the dehydrohalogenation product(s) that result when the following alkyl halides are heated in alcoholic KOH. When more than one product is formed, predict the major and minor products.
(d)
(e)
1501
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Textbook Question
Write a balanced equation for each reaction, showing the major product you expect.
(c)
929
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