Textbook Question
Starting with ethyne, describe how the following compounds can be synthesized:
a. (3S,4R)-4-bromo-3-hexanol and (3R,4S)-4-bromo-3-hexanol
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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 55a
Bruice 8th EditionCh. 7 - The Reactions of Alkynes • An Introduction to Multistep SynthesisProblem 55aChapter 8, Problem 55a
What stereoisomers are obtained from the following reactions?
Verified step by step guidance1
Step 1: Analyze the starting material. The given compound is a terminal alkyne, (CH3)3CH2C≡CCH2(CH3)3. The triple bond is the reactive site in this molecule.
Step 2: Understand the first reaction conditions. Sodium (Na) in liquid ammonia (NH3) at −78°C is a classic setup for the Birch reduction. This reaction selectively reduces alkynes to trans-alkenes. The triple bond will be converted into a trans-alkene.
Step 3: Consider the stereochemistry of the trans-alkene. The two substituents on either side of the triple bond will end up on opposite sides of the double bond after the Birch reduction. This stereochemistry is important for determining the stereoisomers.
Step 4: Understand the second reaction conditions. D2 with Pd/C is a catalytic hydrogenation reaction, but instead of H2, deuterium gas (D2) is used. This reaction will reduce the double bond to a single bond, adding deuterium atoms to the molecule. Since the reduction is catalytic, the addition of deuterium is stereospecific and occurs in a syn fashion.
Step 5: Combine the results of both steps. After the Birch reduction, the molecule will have a trans-alkene configuration. The subsequent catalytic hydrogenation will add deuterium atoms to the molecule, resulting in a fully saturated alkane with specific stereochemistry based on the trans-alkene intermediate.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Stereoisomerism
Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. This can lead to different physical and chemical properties. In organic chemistry, stereoisomers include enantiomers and diastereomers, which are crucial for understanding the behavior of molecules in reactions.
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Determining when molecules are stereoisomers.
Alkyne Hydrogenation
Hydrogenation of alkynes involves the addition of hydrogen (H2) across the triple bond to form alkenes or alkanes. The reaction can be catalyzed by metals such as palladium (Pd) or nickel (Ni). The conditions of the reaction, such as temperature and the presence of solvents, can influence the stereochemistry of the resulting products, leading to the formation of different stereoisomers.
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Reduction with Sodium Ammonia
The reduction of alkynes using sodium in liquid ammonia (Na/NH3) leads to the formation of trans-alkenes. This reaction is characterized by the generation of a radical anion intermediate, which subsequently undergoes protonation. The stereochemistry of the product is important, as it determines the spatial arrangement of substituents around the double bond, influencing the types of stereoisomers formed.
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Related Practice
Textbook Question
A chemist is planning to synthesize 3-octyne by adding 1-bromobutane to the product obtained from the reaction of 1-butyne with sodium amide. Unfortunately, however, he forgot to order 1-butyne. How else can he prepare 3-octyne?
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Textbook Question
What stereoisomers are obtained from the following reactions?
b.
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Textbook Question
Explain why, in hydroboration–oxidation, HO− and HOOH cannot be added until after the hydroboration reaction is over.
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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:
f.
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Textbook Question
a. Explain why a single pure product is obtained from hydroboration–oxidation of 2-butyne, whereas two products are obtained from hydroboration–oxidation of 2-pentyne.
b. Name two other internal alkynes that yield only one product upon hydroboration–oxidation.