Textbook Question
Predict the products formed by sodium hydroxide-promoted dehydrohalogenation of the following compounds. In each case, predict which will be the major product.
d. cis-1-bromo-2-methylcyclohexane
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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 51a,b,c
What halides would undergo E2 dehydrohalogenation to give the following pure alkenes?
a. hex-1-ene
b. isobutylene
c. pent-2-ene
Verified step by step guidance1
Step 1: Understand the E2 elimination mechanism. E2 dehydrohalogenation involves the removal of a hydrogen atom (β-hydrogen) and a halide ion (X⁻) from adjacent carbon atoms in a single concerted step, forming a double bond (alkene). The reaction requires a strong base and a good leaving group (halide).
Step 2: Analyze the structure of the desired alkene (product) and determine the position of the double bond. For each case, identify the β-hydrogen and the halide that must be removed to form the double bond in the product.
Step 3: For hex-1-ene, the double bond is between the first and second carbon atoms. The halide must be attached to the first carbon, and a β-hydrogen must be present on the second carbon. Suitable halides include 1-bromohexane, 1-chlorohexane, or 1-iodohexane.
Step 4: For isobutylene, the double bond is between the second and third carbon atoms in a branched structure. The halide must be attached to the second carbon, and a β-hydrogen must be present on the third carbon. Suitable halides include 2-bromoisobutane, 2-chloroisobutane, or 2-iodoisobutane.
Step 5: For pent-2-ene, the double bond is between the second and third carbon atoms. The halide must be attached to either the second or third carbon, and a β-hydrogen must be present on the adjacent carbon. Suitable halides include 2-bromopentane, 2-chloropentane, or 2-iodopentane.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
E2 Mechanism
The E2 mechanism is a type of elimination reaction where a base removes a proton from a β-carbon while a leaving group (such as a halide) departs from the α-carbon simultaneously. This concerted process results in the formation of a double bond. Understanding the stereochemistry and the requirement for anti-periplanar geometry is crucial for predicting the outcome of E2 reactions.
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09:36
Drawing the E2 Mechanism.
Dehydrohalogenation
Dehydrohalogenation refers to the elimination of a hydrogen halide (HX) from an alkyl halide, leading to the formation of an alkene. This reaction typically requires a strong base and is a key step in synthesizing alkenes from alkyl halides. The choice of base and the structure of the halide influence the reaction pathway and the stability of the resulting alkene.
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03:02The dehydrohalogenation mechanism.
Alkene Stability and Substitution
The stability of alkenes is influenced by their degree of substitution; more substituted alkenes are generally more stable due to hyperconjugation and the inductive effect. This concept is important when predicting which halides will undergo E2 reactions to yield specific alkenes, as the formation of more stable alkenes is favored. Understanding Zaitsev's rule helps in determining the major product in elimination reactions.
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04:28Understanding trends of alkene stability.
Related Practice
Textbook Question
Predict the products formed by sodium hydroxide-promoted dehydrohalogenation of the following compounds. In each case, predict which will be the major product.
a. 1-bromobutane
b. 2-chlorobutane
c. 3-bromopentane
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Textbook Question
What halides would undergo E2 dehydrohalogenation to give the following pure alkenes?
d. methylenecyclohexane
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Textbook Question
Predict the major products of acid-catalyzed dehydration of the following alcohols.
(a)
(b)
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Textbook Question
Predict the products formed by sodium hydroxide-promoted dehydrohalogenation of the following compounds. In each case, predict which will be the major product.
e. trans-1-bromo-2-methylcyclohexane
668
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Textbook Question
What halides would undergo E2 dehydrohalogenation to give the following pure alkenes?
e. 4-methylcyclohexene
588
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