Here are the essential concepts you must grasp in order to answer the question correctly.
Free-Radical Bromination
Free-radical bromination is a reaction where bromine (Br2) reacts with alkanes to form alkyl bromides through a radical mechanism. This process involves three main steps: initiation, propagation, and termination. The reaction begins with the homolytic cleavage of the Br-Br bond, generating bromine radicals that can abstract hydrogen atoms from alkanes, leading to the formation of more stable radicals.
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Using the Hammond Postulate to describe radical bromination.
Radical Stability
The stability of radicals is crucial in predicting the products of free-radical bromination. Radicals are more stable when they are tertiary (attached to three carbon atoms) compared to secondary or primary radicals. This stability influences which hydrogen atoms are abstracted during the reaction, as the formation of the most stable radical intermediate is favored, leading to the major product.
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The radical stability trend.
Selectivity in Bromination
Bromination is known for its selectivity, meaning it preferentially reacts with the most stable radical. This selectivity arises from the energy differences between the various radical intermediates formed during the reaction. As a result, the major product of bromination will be the one derived from the most stable radical, which is typically the one that forms from the most substituted carbon in the alkane.
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Mechanism of Allylic Bromination.