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Ch. 17 - Reactions of Aromatic Compounds
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo
Capitolo 17, Problema 60d

Electrophilic aromatic substitution usually occurs at the 1-position of naphthalene, also called the a position. Predict the major products of the reactions of naphthalene with the following reagents.

(d) isobutylene and HF

Guida verificata passo dopo passo
1
Step 1: Understand the reaction type. The problem involves electrophilic aromatic substitution (EAS), a reaction where an electrophile replaces a hydrogen atom on an aromatic ring. Naphthalene, a polycyclic aromatic hydrocarbon, undergoes EAS preferentially at the 1-position (α position) due to its higher electron density and stability of the intermediate carbocation.
Step 2: Analyze the reagents. Isobutylene (CH₂=C(CH₃)₂) and HF are used in this reaction. HF acts as a catalyst to protonate isobutylene, generating a carbocation (CH₃-C⁺(CH₃)-CH₃), which serves as the electrophile in the EAS reaction.
Step 3: Predict the site of attack. The carbocation electrophile will attack the α position (1-position) of naphthalene because this position leads to the formation of the most stable intermediate carbocation during the reaction.
Step 4: Draw the intermediate. After the electrophile attacks the α position, a resonance-stabilized carbocation intermediate is formed. This intermediate redistributes the positive charge across the aromatic system, stabilizing the structure.
Step 5: Complete the reaction. The final product is formed when the intermediate loses a proton, restoring aromaticity to the naphthalene ring. The major product will be naphthalene substituted at the α position with the isobutyl group (CH₂-C(CH₃)₂).

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Electrophilic Aromatic Substitution (EAS)

Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This reaction typically occurs at positions that are more reactive due to the stability of the aromatic system. In naphthalene, the 1-position (alpha position) is particularly reactive due to its ability to stabilize the positive charge formed during the reaction.
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EAS Review

Naphthalene Structure and Reactivity

Naphthalene is a polycyclic aromatic hydrocarbon consisting of two fused benzene rings. Its structure allows for multiple substitution positions, with the 1-position being the most favorable for electrophilic attack. Understanding the reactivity of naphthalene is crucial for predicting the products of reactions, especially when considering steric and electronic effects.
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Reagents in EAS Reactions

In the context of EAS reactions, reagents such as isobutylene and HF can influence the outcome of the substitution. Isobutylene can act as a source of a carbocation, while HF can provide a protonation step. The nature of these reagents affects the stability of the intermediates and the final products, making it essential to analyze their roles in the reaction mechanism.
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