The mechanism for this kind of reaction involves the formation of free radicals, and the relative stability of different molecules will decide the formation of major and minor products.
Step 1 , Chain initiation :- First of all , the homolytic cleavage takes place in peroxide molecule as shown below :-
Step2 Chain propagation :-
In this step , the bromine free radicals formed in first step 1 attack on the alkene
Step 3 Termination step:-
In this step all the free radicals are consumed and so we get different products.
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