Ch.8 - Reactions of Alkenes

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch.8 - Reactions of Alkenes

Problem 56d

Chapter 8, Problem 56d

Propose mechanisms consistent with the following reactions.
(d)

Verified step by step guidance

Step 1: Recognize the reaction type. This reaction involves the formation of a dibromo-substituted cyclopropane ring from an alkene. The reagents CHBr₃ (bromoform) and NaOH suggest a haloform reaction followed by cyclopropanation.

Step 2: Understand the role of the reagents. NaOH deprotonates CHBr₃ to form the tribromomethyl anion (CBr₃⁻), which is highly nucleophilic and reactive. This intermediate is key to the reaction mechanism.

Step 3: Analyze the alkene's role. The alkene acts as a nucleophile and reacts with the tribromomethyl anion. The π-electrons of the alkene attack the electrophilic carbon of the tribromomethyl group, forming a new bond.

Step 4: Formation of the cyclopropane ring. After the initial attack, two bromine atoms are eliminated from the tribromomethyl group, resulting in the formation of a cyclopropane ring with two bromine substituents attached to the same carbon.

Step 5: Verify the product structure. The final product is a dibromo-substituted cyclopropane ring attached to the benzene ring. This structure is consistent with the reaction mechanism and the given reagents.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In this mechanism, the aromatic system donates electrons to the electrophile, forming a sigma complex, which then loses a proton to restore aromaticity. Understanding EAS is crucial for analyzing reactions involving aromatic compounds, such as the one depicted in the question.

Bromination Mechanism

The bromination mechanism involves the introduction of bromine into an organic compound, typically through the use of brominating agents like CHBr3. In the presence of a base like NaOH, the bromine can be activated to form a more reactive species that can effectively substitute hydrogen atoms on the aromatic ring. This mechanism is essential for understanding how the brominated product is formed in the given reaction.

Regioselectivity in Substitution Reactions

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of electrophilic aromatic substitution, the position where the electrophile attaches to the aromatic ring can be influenced by existing substituents. Recognizing the regioselectivity in the reaction shown helps predict the final structure of the brominated product.

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Related Practice

Textbook Question

Propose mechanisms consistent with the following reactions.

(g)

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Textbook Question

Propose mechanisms consistent with the following reactions.

(c)

1087

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Textbook Question

Propose mechanisms consistent with the following reactions.

(f)

1520

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Textbook Question

Draw an approximate reaction-energy diagram showing the curves for the two possible pathways for ionic addition of HBr to 1-methylcyclohexene. (a) Formation of the major product, 1-bromo-1-methylcyclohexane, and (b) formation of the minor product, 1-bromo-2-methylcyclohexane. Point out how these curves show that 1-bromo-1-methylcyclohexane should be formed faster.

2055

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Textbook Question

Propose mechanisms consistent with the following reactions.

(b)

996

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Textbook Question

Propose mechanisms consistent with the following reactions.

(a)

1360

views