Textbook Question
a. What alkene is required to synthesize each of the following compounds?
b. What other epoxide is formed in each synthesis?
c. Assign an R or S configuration to each asymmetric center.
2.
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Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions
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. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 42c
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 42cChapter 7, Problem 42c
What stereoisomers are obtained from hydroboration–oxidation of the following compounds? Assign an R or S configuration to each asymmetric center.
c. cis-2-butene
Verified step by step guidance1
Identify the reaction: Hydroboration–oxidation is a two-step reaction. The first step involves the addition of borane (BH₃) to the alkene, and the second step involves oxidation with hydrogen peroxide (H₂O₂) in a basic medium (NaOH). This reaction proceeds via anti-Markovnikov addition, where the hydroxyl group (-OH) attaches to the less substituted carbon of the double bond.
Analyze the starting material: cis-2-butene is a symmetrical alkene with the double bond between carbons 2 and 3. The two methyl groups are on the same side of the double bond, making it a cis isomer.
Determine the stereochemistry of the product: Hydroboration–oxidation occurs with syn addition, meaning that both the hydrogen (H) and hydroxyl group (-OH) are added to the same face of the double bond. This syn addition will result in the formation of a pair of enantiomers (stereoisomers) because the starting material is symmetrical.
Assign R or S configuration: After the addition of -OH and H, the product will have two chiral centers (at carbons 2 and 3). To assign R or S configuration, prioritize the substituents on each chiral center based on the Cahn-Ingold-Prelog rules. Assign priorities to the groups attached to each chiral center, determine the direction of rotation (clockwise or counterclockwise), and assign R (clockwise) or S (counterclockwise) accordingly.
Conclude the stereoisomers: The reaction will yield a racemic mixture of two enantiomers, one with (2R,3R) configuration and the other with (2S,3S) configuration, due to the symmetrical nature of the starting material and the syn addition mechanism.
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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 those atoms. This can lead to different physical and chemical properties. In organic chemistry, stereoisomers include enantiomers and diastereomers, which are crucial for understanding reactions involving chiral centers.
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Determining when molecules are stereoisomers.
Hydroboration-Oxidation
Hydroboration-oxidation is a two-step reaction process used to convert alkenes into alcohols. In the first step, borane (BH3) adds across the double bond of the alkene, resulting in a trialkylborane intermediate. The second step involves oxidation with hydrogen peroxide (H2O2) in a basic solution, leading to the formation of an alcohol. This reaction is stereospecific and results in anti-Markovnikov addition.
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R and S Configuration
The R and S configuration system is used to describe the absolute configuration of chiral centers in molecules. To assign R or S, the substituents attached to the chiral carbon are ranked according to their atomic number. The configuration is determined by the orientation of the highest priority substituent: if it is clockwise, the configuration is R; if counterclockwise, it is S. This is essential for understanding the stereochemistry of the products formed in reactions.
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Related Practice
Textbook Question
What stereoisomers are obtained from hydroboration–oxidation of the following compounds? Assign an R or S configuration to each asymmetric center.
a. cyclohexene
b. 1-ethylcyclohexene
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Textbook Question
What stereoisomers are obtained from hydroboration–oxidation of the following compounds? Assign an R or S configuration to each asymmetric center.
d. (Z)-3,4-dimethyl-3-hexene
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Textbook Question
The reaction of 2-ethyl-1-pentene with Br2, with H2 + Pd/C, or with R2BH/THF followed by aqueous HO- + H2O2 leads to a racemic mixture. Explain why a racemic mixture is obtained in each case.
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Textbook Question
Using a sample of trans-2-pentene, how could you prove that the addition of Br2 forms a cyclic bromonium ion intermediate rather than a carbocation intermediate?
1366
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Textbook Question
a. What alkene is required to synthesize each of the following compounds?
b. What other epoxide is formed in each synthesis?
c. Assign an R or S configuration to each asymmetric center.
1.
1057
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