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Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Bruice 8th EditionCh. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions문제 42a,b
6장, 문제 42a,b

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

검증된 단계별 안내
1
Step 1: Understand the hydroboration–oxidation reaction. This reaction involves two steps: (1) hydroboration, where BH₃ (borane) adds across the double bond in a syn-addition manner, and (2) oxidation, where the boron atom is replaced by an OH group using hydrogen peroxide (H₂O₂) and a base (e.g., NaOH). The reaction proceeds with anti-Markovnikov regioselectivity, meaning the OH group attaches to the less substituted carbon of the double bond.
Step 2: Analyze the structure of cyclohexene. Cyclohexene is a cyclic alkene with one double bond. During hydroboration–oxidation, the OH group will add to the less substituted carbon of the double bond, and the H will add to the more substituted carbon. Since the addition is syn, both groups will add to the same face of the ring, creating a single stereoisomer. Assign R or S configuration to the resulting chiral center by prioritizing substituents based on the Cahn-Ingold-Prelog rules.
Step 3: Analyze the structure of 1-ethylcyclohexene. This compound has a double bond in the cyclohexene ring and an ethyl group attached to the ring. During hydroboration–oxidation, the OH group will add to the less substituted carbon of the double bond (the carbon not attached to the ethyl group), and the H will add to the more substituted carbon. Again, the addition is syn, so both groups will add to the same face of the ring. This reaction will produce two stereoisomers (enantiomers) because the product will have two chiral centers. Assign R or S configurations to each chiral center by following the Cahn-Ingold-Prelog rules.
Step 4: Assign priorities to the substituents on each chiral center. For each chiral center, identify the four groups attached to it and rank them based on atomic number. If two atoms are the same, move outward along the chain until a difference is found. Use these priorities to determine the configuration (R or S) by orienting the molecule so that the lowest-priority group is pointing away from you and tracing a path from the highest to the lowest priority.
Step 5: Verify the stereochemistry of the products. For cyclohexene, confirm the single stereoisomer and its configuration. For 1-ethylcyclohexene, confirm the two stereoisomers (enantiomers) and assign R or S configurations to both chiral centers in each stereoisomer. Ensure that the configurations are consistent with the syn-addition mechanism of hydroboration–oxidation.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

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 can be classified into enantiomers and diastereomers, which are crucial for understanding the behavior of compounds in reactions such as hydroboration–oxidation.
추천 영상:
01:58
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. This reaction is stereospecific and leads to syn-addition, which is important for determining the stereochemistry of the products.
추천 영상:
06:38
General 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, the substituents attached to the chiral carbon are ranked according to their atomic number, with the highest priority assigned first. The orientation of the molecule is then analyzed: if the lowest priority group is positioned at the back and the sequence of the remaining groups is clockwise, the configuration is R; if counterclockwise, it is S. This is essential for accurately describing the stereoisomers produced in the hydroboration–oxidation reaction.
추천 영상:
03:07
R and S Naming- Step 4
관련 실천
교과서 질문

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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교과서 질문

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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교과서 질문

a. What stereoisomers are formed in the following reaction? Are they enantiomers or diastereomers?

b. Which stereoisomer is formed in greater yield?

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교과서 질문

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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교과서 질문

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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교과서 질문

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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