Textbook Question
The introduction of elimination reactions provides a second way to synthesize alkynes in a two-step process starting with an alkene. Suggest a mechanism for both steps of this process.
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Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 12 - Substitution and Elimination: Reactions of HaloalkanesProblem 60b
Mullins 1st EditionCh. 12 - Substitution and Elimination: Reactions of HaloalkanesProblem 60bChapter 11, Problem 60b
Suggest a bromoalkane and the conditions necessary to produce the alkenes shown.
(b) 
Verified step by step guidance1
Analyze the product structure: The product is an alkene with a phenyl group (Ph) attached to the carbon chain. The double bond is located between two carbons in the chain.
Determine the precursor: To form this alkene, a bromoalkane with the bromine atom attached to the carbon adjacent to the double bond in the product is required. This is because elimination reactions typically occur at the β-hydrogen relative to the halogen.
Select the reaction type: The formation of alkenes from bromoalkanes is commonly achieved through an elimination reaction, such as an E2 mechanism. This requires a strong base to abstract a β-hydrogen and promote the elimination of the bromine atom.
Choose the conditions: Use a strong base like potassium tert-butoxide (K⁺[CH₃]₃CO⁻) in a polar aprotic solvent such as dimethyl sulfoxide (DMSO) or ethanol. Heat is often applied to favor elimination over substitution.
Verify regioselectivity: The reaction conditions should favor the formation of the more substituted alkene (Zaitsev's rule), which is the major product in elimination reactions. Ensure the base and solvent are chosen to promote this outcome.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Bromoalkanes
Bromoalkanes are organic compounds containing a bromine atom attached to an alkane chain. They are often used as intermediates in organic synthesis, particularly in reactions that form alkenes through elimination processes. Understanding the structure and reactivity of bromoalkanes is crucial for predicting the products of reactions involving them.
Elimination Reactions
Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond. In the context of bromoalkanes, these reactions typically occur under conditions such as heating with a strong base, leading to the formation of alkenes. The mechanism can be either E1 or E2, depending on the substrate and conditions.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others. In the formation of alkenes from bromoalkanes, the regioselectivity can be influenced by the stability of the resulting double bond and the sterics of the substituents. Understanding regioselectivity is essential for predicting the major products in elimination reactions.
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Related Practice
Textbook Question
Suggest a bromoalkane and the conditions necessary to produce the alkenes shown.
(a)
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Textbook Question
In Chapter 10, you learned how to make an alkyne by acetylide alkylation with a 1° haloalkane. Suggest a mechanism by which this reaction occurs.
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Textbook Question
Acetylide alkylation, from Assessment 12.61, fails to give the desired product with 2° haloalkanes. Why? What is the actual product of this reaction?
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Textbook Question
For each pair, choose the haloalkane that would react most quickly in an SN1 or E1 reaction.
(b)
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Textbook Question
For each pair, choose the haloalkane that would react most quickly in an Sₙ1 or E1 reaction.
(c)
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