Predict the major product(s) of the following allylic bromination reactions.
(c)

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Identify the allylic position in the given molecule. The allylic position is the carbon atom adjacent to a double bond.

Understand that allylic bromination involves the substitution of a hydrogen atom at the allylic position with a bromine atom, typically using N-bromosuccinimide (NBS) in the presence of light or heat.

Consider the resonance stabilization of the allylic radical formed during the reaction. The allylic radical can delocalize the unpaired electron over the π system, leading to multiple resonance structures.

Determine the most stable resonance structure, which will guide you to predict the major product. The stability is often influenced by the degree of substitution of the radical and the overall stability of the resulting product.

Predict the major product by substituting the bromine atom at the most stable allylic position, considering the resonance structures and the stability of the resulting brominated compound.

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Key Concepts

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

Allylic Bromination

Allylic bromination is a type of radical substitution reaction where a bromine atom is introduced at the allylic position of an alkene. This position is adjacent to the double bond, and the reaction typically involves the use of N-bromosuccinimide (NBS) in the presence of light or heat to generate bromine radicals that facilitate the substitution.

Radical Mechanism

The radical mechanism is crucial for understanding allylic bromination. It involves the formation of a bromine radical, which abstracts a hydrogen atom from the allylic position, creating an allylic radical. This radical then reacts with another bromine molecule to form the brominated product. The stability of the allylic radical is key to predicting the major product.

Regioselectivity in Allylic Bromination

Regioselectivity refers to the preference for the formation of one constitutional isomer over others in a chemical reaction. In allylic bromination, the most stable allylic radical is formed preferentially, leading to the major product. Factors such as resonance stabilization and steric effects influence which allylic position is brominated, guiding the prediction of the major product.

Predict the major product(s) of the following allylic bromination reactions. (c)