Textbook Question
What stereoisomers are obtained when 2-butyne undergoes each of the following reaction sequences?
c. 1. Cl2/CH2Cl2 2. Br2/CH2Cl2
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Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 7 - The Reactions of Alkynes • An Introduction to Multistep SynthesisProblem 50a
Bruice 8th EditionCh. 7 - The Reactions of Alkynes • An Introduction to Multistep SynthesisProblem 50aChapter 8, Problem 50a
Show how the following compounds can be synthesized starting with ethyne:
a. cis-2-octene
Verified step by step guidance1
Step 1: Start with ethyne (C₂H₂), which is a terminal alkyne. The first step is to elongate the carbon chain. Perform a reaction with sodium amide (NaNH₂) to deprotonate the terminal hydrogen of ethyne, forming the acetylide ion (C≡C⁻).
Step 2: React the acetylide ion with 1-bromobutane (CH₃CH₂CH₂CH₂Br) in an SN2 reaction. This will result in the formation of 1-hexyne (CH₃CH₂CH₂CH₂C≡CH), which is a longer alkyne chain.
Step 3: To convert the terminal alkyne into an internal alkyne, perform another alkylation. Deprotonate the terminal hydrogen of 1-hexyne using sodium amide (NaNH₂) to form the corresponding acetylide ion. Then react this ion with ethyl bromide (CH₃CH₂Br) to form 3-octyne (CH₃CH₂CH₂CH₂C≡CCH₂CH₃).
Step 4: Reduce the triple bond of 3-octyne to a cis double bond. Use Lindlar's catalyst (Pd/CaCO₃ poisoned with quinoline) and hydrogen gas (H₂) to selectively hydrogenate the alkyne to cis-2-octene (CH₃CH₂CH₂CH₂CH=CHCH₂CH₃).
Step 5: Verify the stereochemistry of the product. Lindlar's catalyst ensures the formation of the cis isomer of the alkene, so the final product is cis-2-octene.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Ethyne as a Building Block
Ethyne, also known as acetylene, is a simple alkyne that serves as a versatile building block in organic synthesis. Its triple bond allows for various reactions, including addition reactions with electrophiles, which can lead to the formation of more complex molecules. Understanding how to manipulate ethyne's reactivity is crucial for synthesizing larger compounds like cis-2-octene.
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Hydroboration-Oxidation
The hydroboration-oxidation reaction is a two-step process used to convert alkenes into alcohols. In the first step, borane adds to the alkene, resulting in a trialkylborane intermediate. The subsequent oxidation with hydrogen peroxide and sodium hydroxide converts the boron to a hydroxyl group, yielding an alcohol. This method is particularly useful for synthesizing specific stereoisomers, such as cis-2-octene.
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Stereochemistry of Alkenes
Stereochemistry refers to the spatial arrangement of atoms in molecules and is crucial in determining the properties and reactivity of alkenes. For cis-2-octene, the 'cis' designation indicates that the substituents on the double bond are on the same side, which affects its physical properties and reactivity. Understanding stereochemistry is essential for predicting the outcomes of reactions and for synthesizing specific isomers.
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Related Practice
Textbook Question
What stereoisomers are obtained when 2-butyne undergoes each of the following reaction sequences?
a. 1. H2/Lindlar catalyst 2. Br2/CH2Cl2
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Textbook Question
Show how the following compounds can be synthesized starting with ethyne:
b. trans-3-heptene
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Textbook Question
Show how each of the following compounds can be prepared using the given starting material, any needed inorganic reagents, and any organic compound that has no more than four carbons:
b.
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Textbook Question
Show how each of the following compounds can be prepared using the given starting material, any needed inorganic reagents, and any organic compound that has no more than four carbons:
a.
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Textbook Question
What is each compound's systematic name?
c.
d.
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