Textbook Question
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
19. Reactions of Aromatics: EAS and Beyond
EAS:Friedel-Crafts Alkylation Mechanism
Problem 32d
Textbook Question
Predict the product of the following Friedel–Crafts alkylation reactions. Assume only one alkyl group adds in each case.
(d) 
Verified step by step guidance1
Identify the reactants: The reaction involves benzene and chlorocyclopentane in the presence of aluminum chloride (AlCl₃) as a catalyst.
Understand the mechanism: Friedel-Crafts alkylation involves the formation of a carbocation intermediate. The chlorine atom in chlorocyclopentane will leave, forming a cyclopentyl carbocation.
Consider carbocation stability: The cyclopentyl carbocation is relatively stable and will act as the electrophile in the reaction.
Electrophilic aromatic substitution: The cyclopentyl carbocation will attack the benzene ring, forming a sigma complex (arenium ion) and eventually leading to the substitution of a hydrogen atom on the benzene ring with the cyclopentyl group.
Predict the product: The final product will be cyclopentylbenzene, where the cyclopentyl group is attached to the benzene ring.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Friedel-Crafts Alkylation
Friedel-Crafts alkylation is a reaction that introduces an alkyl group into an aromatic ring using an alkyl halide and a Lewis acid catalyst, typically aluminum chloride (AlCl3). This electrophilic substitution reaction allows for the formation of new carbon-carbon bonds, enhancing the complexity of aromatic compounds. However, it can lead to polysubstitution and rearrangements, so careful control of conditions is necessary.
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Friedel-Crafts Alkylation
Electrophilic Aromatic Substitution
Electrophilic aromatic substitution (EAS) is a fundamental reaction mechanism in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. The aromatic system's electron-rich nature makes it susceptible to attack by electrophiles, leading to the formation of a sigma complex. This mechanism is crucial for understanding how substituents affect the reactivity and orientation of further substitutions on the aromatic ring.
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Rearrangement of Carbocations
In Friedel-Crafts reactions, the formation of carbocations is a key step, and these intermediates can undergo rearrangement to form more stable structures. For instance, if a secondary or tertiary carbocation is formed, it may rearrange to a more stable tertiary carbocation before reacting with the aromatic ring. Understanding carbocation stability and rearrangement is essential for predicting the products of alkylation reactions.
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00:47Understanding why carbocations shift.
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