Textbook Question
What stereoisomers are obtained from the following reactions?
c. (E)-3-methyl-2-pentene + HBr
d. cis-3-hexene + HBr
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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 42d
Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition ReactionsProblem 42dChapter 7, Problem 42d
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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Analyze the structure of the given compound, (Z)-3,4-dimethyl-3-hexene. The (Z) configuration indicates that the higher-priority groups on either side of the double bond are on the same side. Draw the structure to visualize the stereochemistry of the starting material.
Understand the hydroboration–oxidation reaction. This reaction involves two steps: (1) addition of BH₃ (borane) to the double bond in an anti-Markovnikov manner, where the boron adds to the less substituted carbon, and (2) oxidation with H₂O₂/NaOH, replacing the boron with an -OH group. The reaction proceeds with syn addition, meaning both the hydrogen and the hydroxyl group add to the same face of the double bond.
Determine the stereochemistry of the product. Since the reaction is stereospecific and proceeds with syn addition, the two new substituents (H and OH) will be added to the same side of the double bond. This creates two new chiral centers at carbons 3 and 4 of the hexane chain.
Assign the R or S configuration to each chiral center. To do this, prioritize the groups attached to each chiral center based on the Cahn-Ingold-Prelog rules. Assign priorities (1 to 4) to the substituents, orient the lowest-priority group (usually hydrogen) away from you, and determine whether the sequence of priorities 1 → 2 → 3 is clockwise (R) or counterclockwise (S). Repeat this process for both chiral centers.
List all possible stereoisomers. Since two chiral centers are formed, there will be four possible stereoisomers (two pairs of enantiomers). However, the syn addition of hydroboration–oxidation limits the stereoisomers to a specific pair of enantiomers. Verify the configurations of the resulting stereoisomers and confirm their R or S designations for each chiral center.
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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 like hydroboration-oxidation.
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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. The first step involves the addition of borane (BH3) to 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 alcohols with anti-Markovnikov orientation, which is essential for determining the stereochemistry of the product.
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06:38General properties of hydroboration-oxidation.
R and S Configuration
The R and S configuration system is used to describe the stereochemistry of chiral centers in molecules. To assign R or S, one must prioritize the substituents attached to the chiral carbon based on atomic number, then determine the orientation of the molecule. If the lowest priority group is oriented away from the viewer, the configuration is determined by the order of the remaining groups; clockwise is R and counterclockwise is S.
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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
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?
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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.
c. cis-2-butene
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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.
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