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Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl Halides문제 36
9장, 문제 36

Why do cis-1-bromo-2-ethylcyclohexane and trans-1-bromo-2-ethylcyclohexane form different major products when they undergo an E2 reaction?

검증된 단계별 안내
1
Understand the E2 reaction mechanism: The E2 (bimolecular elimination) reaction involves the simultaneous removal of a β-hydrogen and a leaving group (in this case, bromine) to form a double bond. The reaction requires an anti-periplanar geometry, where the β-hydrogen and the leaving group are in opposite planes (one axial up and the other axial down in a cyclohexane ring).
Analyze the conformations of cis-1-bromo-2-ethylcyclohexane: In the cis isomer, the bromine atom and the ethyl group are on the same side of the cyclohexane ring. When the molecule adopts a chair conformation, the bromine will be in an axial position, and the ethyl group will be in an equatorial position. This allows for an anti-periplanar β-hydrogen to be available for elimination.
Analyze the conformations of trans-1-bromo-2-ethylcyclohexane: In the trans isomer, the bromine atom and the ethyl group are on opposite sides of the cyclohexane ring. In the chair conformation, the bromine will be in an equatorial position, and the ethyl group will be in an axial position. This changes the availability of anti-periplanar β-hydrogens for elimination.
Determine the major product for each isomer: In the cis isomer, the anti-periplanar geometry allows for elimination to occur more readily, leading to the formation of a specific alkene. In the trans isomer, the equatorial position of the bromine limits the availability of anti-periplanar β-hydrogens, which can lead to a different major product or a less favorable elimination pathway.
Conclude why the products differ: The difference in the spatial arrangement of substituents (cis vs. trans) affects the anti-periplanar geometry required for the E2 reaction. This results in different β-hydrogens being eliminated and, consequently, different alkenes being formed as the major products for the cis and trans isomers.

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영상 길이:
9m

주요 개념

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

E2 Reaction Mechanism

The E2 (bimolecular elimination) reaction is a concerted mechanism where a base abstracts a proton while a leaving group departs, resulting in the formation of a double bond. The stereochemistry of the reactants significantly influences the outcome, as the reaction requires an anti-periplanar arrangement of the leaving group and the hydrogen being removed.
추천 영상:
09:36
Drawing the E2 Mechanism.

Stereochemistry of Substituents

Cis and trans isomers differ in the spatial arrangement of their substituents around a ring or double bond. In the case of 1-bromo-2-ethylcyclohexane, the relative positions of the bromine and ethyl groups affect the accessibility of the hydrogen atoms for elimination, leading to different major products in the E2 reaction based on whether the substituents are on the same side (cis) or opposite sides (trans).
추천 영상:
가이드 코스
1:38
Polymer Stereochemistry Concept 1

Regioselectivity and Stereoselectivity

Regioselectivity refers to the preference for the formation of one structural isomer over others in a chemical reaction, while stereoselectivity indicates the preference for one stereoisomer over another. In the E2 reaction of cis- and trans-1-bromo-2-ethylcyclohexane, the spatial arrangement of substituents leads to different major products due to these selectivity principles, influencing which double bond is formed.
추천 영상:
05:09
Heck Reaction
관련 실천
교과서 질문

What is the major product formed when the following compounds undergo an E1 reaction?

c.

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교과서 질문

Draw the substitution and elimination products for the following reactions, showing the configuration of each product:

b. cis-1-chloro-2-methylcyclohexane + CH3O−

1405
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교과서 질문

What is the major product formed when the following compounds undergo an E1 reaction?

b.

1168
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교과서 질문

What is the major product formed when the following compounds undergo an E1 reaction?

a.

1236
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교과서 질문

Which isomer reacts more rapidly in an E2 reaction: cis-1-bromo-4-tert-butylcyclohexane or trans-1-bromo-4-tert-butylcyclohexane? Explain your answer.

1140
views
교과서 질문

Draw the substitution and elimination products for the following reactions, showing the configuration of each product:

a. trans-1-chloro-2-methylcyclohexane + CH3O−

1895
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