Predict the major products formed when benzene reacts (just once) with the following reagents.
(h) benzoyl chloride + AlCl₃

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Recognize that the reaction involves benzene and benzoyl chloride in the presence of AlCl₃, which is a Friedel-Crafts acylation reaction. This reaction introduces an acyl group onto the benzene ring.

Understand the role of AlCl₃ as a Lewis acid catalyst. It reacts with benzoyl chloride (C₆H₅COCl) to generate the acylium ion (C₆H₅CO⁺), which is the electrophile in this reaction.

Write the mechanism: The acylium ion (C₆H₅CO⁺) is formed when AlCl₃ coordinates with the chlorine atom of benzoyl chloride, causing the Cl to leave as AlCl₄⁻.

Show the electrophilic aromatic substitution (EAS) step: The benzene ring donates a pair of π-electrons to the acylium ion, forming a resonance-stabilized carbocation intermediate.

Conclude the reaction: The intermediate loses a proton (H⁺), and the aromaticity of the benzene ring is restored. The major product is benzophenone (C₆H₅COC₆H₆), and AlCl₃ is regenerated in the process.

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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 mechanism in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In this process, the aromatic system retains its stability and aromaticity, making it a key reaction for modifying aromatic compounds. Understanding EAS is crucial for predicting the products of reactions involving benzene and electrophiles.

Friedel-Crafts Acylation

Friedel-Crafts acylation is a specific type of electrophilic aromatic substitution where an acyl group is introduced into an aromatic ring using an acyl chloride and a Lewis acid catalyst, such as AlCl3. This reaction results in the formation of ketones and is significant for synthesizing aromatic ketones. Recognizing this reaction helps in predicting the product when benzene reacts with benzoyl chloride.

Role of Lewis Acids

Lewis acids, such as AlCl3, are substances that can accept an electron pair from a Lewis base to form a coordinate covalent bond. In the context of Friedel-Crafts reactions, the Lewis acid activates the acyl chloride, generating a more reactive electrophile that can effectively attack the aromatic ring. Understanding the role of Lewis acids is essential for grasping how they facilitate electrophilic aromatic substitution reactions.

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