Textbook Question
What reagents would you use for the following syntheses?
c. hexane from 3-hexyne
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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 38b
Bruice 8th EditionCh. 7 - The Reactions of Alkynes • An Introduction to Multistep SynthesisProblem 38bChapter 8, Problem 38b
What reagents would you use for the following syntheses?
b. (E)-3-hexene from 3-hexyne
Verified step by step guidance1
Step 1: Begin by understanding the transformation required. The goal is to convert 3-hexyne (a triple bond) into (E)-3-hexene (a double bond with trans stereochemistry). This involves selective reduction of the alkyne to an alkene with control over stereochemistry.
Step 2: To achieve the (E)-configuration (trans alkene), use a dissolving metal reduction. This method typically involves reagents such as sodium (Na) in liquid ammonia (NH₃). The dissolving metal reduction selectively produces the trans alkene due to the mechanism of electron transfer and protonation.
Step 3: Write the reaction mechanism. The dissolving metal reduction involves the addition of electrons from sodium to the alkyne, forming a radical anion intermediate. Protonation from ammonia then leads to the trans alkene.
Step 4: Ensure stereochemical control. The dissolving metal reduction is preferred for forming the (E)-alkene because it minimizes steric hindrance and stabilizes the trans configuration during the reaction.
Step 5: Verify the product. After the reaction, confirm that the product is (E)-3-hexene by analyzing its stereochemistry using techniques such as NMR spectroscopy or IR spectroscopy to ensure the double bond is in the trans configuration.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alkyne to Alkene Conversion
The conversion of alkynes to alkenes typically involves a process called hydrogenation or partial hydrogenation. In this case, 3-hexyne, a terminal alkyne, can be converted to (E)-3-hexene by using a reagent that selectively adds hydrogen across the triple bond, resulting in the formation of a double bond while maintaining the desired stereochemistry.
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Stereochemistry of Alkenes
Stereochemistry refers to the spatial arrangement of atoms in molecules and is crucial in determining the properties of alkenes. The (E) designation indicates that the higher priority substituents on either side of the double bond are on opposite sides, which can be achieved through careful selection of reagents during the synthesis process to ensure the correct geometric isomer is formed.
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Reagents for Selective Hydrogenation
To achieve the selective hydrogenation of 3-hexyne to (E)-3-hexene, specific catalysts such as Lindlar's catalyst (palladium on calcium carbonate) can be used. This catalyst allows for the partial hydrogenation of alkynes to alkenes without fully saturating the double bond, thus preserving the desired alkene configuration.
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Related Practice
Textbook Question
How can the following compounds be synthesized, starting with a hydrocarbon that has the same number of carbons as the desired product?
b. CH3CH2CH2CH2OH
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Textbook Question
How can the following compounds be synthesized, starting with a hydrocarbon that has the same number of carbons as the desired product?
c.
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Textbook Question
What reagents would you use for the following syntheses?
a. (Z)-3-hexene from 3-hexyne
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Textbook Question
What is the major product of the reaction of 1 mol of propyne with each of the following reagents?
d. Br2 (2 mol)/CH2Cl2
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Textbook Question
What is the major product of the reaction of 1 mol of propyne with each of the following reagents?
c. Br2 (1 mol)/CH2Cl2
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