Predict the product of the following benzylic bromination reactions.
(c)

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Identify the type of reaction: This is a benzylic bromination reaction, which typically involves the substitution of a hydrogen atom at the benzylic position with a bromine atom.

Locate the benzylic position: The benzylic position is the carbon atom directly attached to the benzene ring. In this case, identify the carbon atom that is adjacent to the benzene ring.

Consider the mechanism: Benzylic bromination usually proceeds via a radical mechanism. The presence of a benzene ring stabilizes the radical intermediate, making the benzylic position more reactive.

Initiate the reaction: The reaction is typically initiated by a radical initiator, such as N-bromosuccinimide (NBS) in the presence of light or heat, which generates bromine radicals.

Predict the product: The bromine radical will abstract a hydrogen atom from the benzylic position, forming a benzylic radical. This radical will then react with another bromine molecule to form the brominated product at the benzylic position.

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Key Concepts

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

Benzylic Bromination

Benzylic bromination is a type of radical halogenation reaction where a bromine atom is introduced at the benzylic position of an aromatic compound. This position is adjacent to the aromatic ring, and the reaction typically involves the use of N-bromosuccinimide (NBS) in the presence of a radical initiator like light or heat. The benzylic position is particularly reactive due to the stability of the benzylic radical formed during the reaction.

Radical Mechanism

Radical mechanisms involve the formation and reaction of radicals, which are species with unpaired electrons. In benzylic bromination, the process begins with the generation of a bromine radical, which abstracts a hydrogen atom from the benzylic position, forming a benzylic radical. This radical then reacts with another bromine molecule to form the brominated product. Understanding radical stability and propagation steps is crucial for predicting the outcome of such reactions.

Stability of Benzylic Radicals

The stability of benzylic radicals is a key factor in benzylic bromination reactions. Benzylic radicals are stabilized by resonance, as the unpaired electron can be delocalized over the aromatic ring. This resonance stabilization makes the benzylic position more reactive compared to other positions on the aromatic ring, facilitating the formation of the radical and subsequent bromination. Recognizing this stability helps in predicting the preferred site of bromination in complex molecules.

Predict the product of the following benzylic bromination reactions. (c)