Predict the product(s) of each of the following multistep reactions.
(b)

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Identify the first step as a Friedel-Crafts acylation reaction. The reactant is an isopropylbenzene (cumene) and the acylating agent is an acyl chloride in the presence of AlCl3, a Lewis acid catalyst.

In the Friedel-Crafts acylation, the acyl chloride reacts with AlCl3 to form an acylium ion, which is a strong electrophile. This electrophile will attack the aromatic ring of cumene, specifically at the para position relative to the isopropyl group due to steric and electronic effects.

After the acylation, the aromatic ring will have an acyl group (a ketone) attached at the para position. This completes the first step of the reaction.

The second step involves N-bromosuccinimide (NBS) in the presence of light, which is a condition for radical bromination. This step will selectively brominate the benzylic position of the alkyl chain attached to the aromatic ring.

The final product will have a bromine atom at the benzylic position of the isopropyl group, resulting from the radical bromination. The aromatic ring will also have the acyl group attached at the para position from the first step.

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Key Concepts

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

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. In this reaction, 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 predicting products in reactions involving aromatic compounds, such as the one shown in the question.

Reagents and Conditions

The choice of reagents and reaction conditions significantly influences the outcome of organic reactions. In the provided reaction, aluminum chloride (AlCl3) acts as a Lewis acid catalyst, facilitating the formation of the electrophile from the chlorinated compound. Additionally, N-bromosuccinimide (NBS) in the presence of light is used for bromination, which is a radical substitution process. Recognizing how these reagents interact is essential for predicting the final products.

Radical Mechanisms

Radical mechanisms involve reactions that proceed through the formation of free radicals, which are highly reactive species with unpaired electrons. In the second step of the reaction, NBS generates bromine radicals under light, which can abstract hydrogen atoms from the substrate, leading to the formation of brominated products. Understanding radical mechanisms is important for predicting the outcomes of reactions that involve radical intermediates.

Predict the product(s) of each of the following multistep reactions.(b)