The mechanism of electrophilic addition of hydrogen bromide HBr to propene in the presence of a peroxide catalyst is known as the free radical mechanism. The presence of a peroxide catalyst leads to the formation of bromine radicals, which then initiate the reaction. The mechanism can be divided into three main steps: initiation, propagation, and termination.1. Initiation:In the presence of a peroxide catalyst, the H-Br bond undergoes homolytic cleavage, generating two bromine radicals Br .ROOR peroxide + HBr ROOH + Br2. Propagation:a The bromine radical Br reacts with the propene molecule, attacking the double bond and forming a new carbon-bromine bond. This process generates a secondary carbon radical.Br + CH2=CH-CH3 propene CH2Br-CH-CH3b The secondary carbon radical reacts with another HBr molecule, abstracting a hydrogen atom and forming a new carbon-hydrogen bond. This step regenerates a bromine radical Br , which can continue the propagation process.CH2Br-CH-CH3 + HBr CH2Br-CH2-CH3 1-bromopropane + Br3. Termination:The reaction terminates when two radicals collide and form a new bond. This can occur in several ways, such as the combination of two bromine radicals, two carbon radicals, or a bromine radical with a carbon radical.Br + Br Br2CH2Br-CH-CH3 + Br CH2Br-CHBr-CH3 1,2-dibromopropane CH2Br-CH-CH3 + CH2Br-CH-CH3 CH2Br-CH2-CH3 + CH2Br-CH2-CH3 1-bromopropane In summary, the electrophilic addition of HBr to propene in the presence of a peroxide catalyst follows a free radical mechanism, which involves initiation, propagation, and termination steps. The presence of the peroxide catalyst leads to the formation of bromine radicals, which initiate the reaction and ultimately result in the formation of 1-bromopropane.