Here are the essential concepts you must grasp in order to answer the question correctly.
Allylic Bromination
Allylic bromination is a reaction where bromine is introduced at the allylic position of an alkene. This position is adjacent to the double bond, allowing for resonance stabilization of the radical intermediate formed during the reaction. The use of N-bromosuccinimide (NBS) in the presence of heat facilitates the generation of bromine radicals necessary for this transformation.
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Mechanism of Allylic Bromination.
Radical Mechanism
The radical mechanism involves the formation of radical intermediates, which are highly reactive species with unpaired electrons. In allylic bromination, the reaction proceeds through a radical chain mechanism, starting with the homolytic cleavage of NBS to generate bromine radicals, which then abstract hydrogen from the allylic position, forming a stabilized allylic radical that reacts with bromine to form the brominated product.
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The mechanism of Radical Polymerization.
Resonance Stabilization
Resonance stabilization is a key concept in organic chemistry where certain intermediates, such as radicals or carbocations, are stabilized by the delocalization of electrons across adjacent pi systems. In allylic bromination, the allylic radical formed is stabilized by resonance, allowing the radical to be distributed over multiple atoms, which lowers the energy of the intermediate and facilitates the reaction.
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The radical stability trend.