The addition reaction between an alkene and hydrogen bromide HBr in the presence of peroxide ROOR follows a radical mechanism known as the "anti-Markovnikov" addition. This reaction is also called the "peroxide effect" or "Kharasch effect." The mechanism involves the following steps:1. Initiation: The reaction begins with the homolytic cleavage of the peroxide ROOR by heat or light, generating two alkoxy radicals RO .ROOR 2 RO2. Reaction of the alkoxy radical with HBr: The alkoxy radical reacts with HBr, breaking the H-Br bond and generating a bromine radical Br and an alcohol ROH .RO + HBr ROH + Br3. Reaction of the bromine radical with the alkene: The bromine radical reacts with the alkene, forming a new carbon-bromine bond and generating a carbon-centered radical at the less substituted carbon of the alkene anti-Markovnikov position .Br + RCH=CHR' RCHBr-CHR'4. Reaction of the carbon-centered radical with HBr: The carbon-centered radical reacts with another HBr molecule, forming a new carbon-hydrogen bond and regenerating the bromine radical.RCHBr-CHR' + HBr RCHBr-CH R' Br + Br5. Termination: The reaction can be terminated by the combination of two radicals, such as the bromine radical and the carbon-centered radical, or by the reaction of the bromine radical with the alkoxy radical.Br + RCHBr-CHR' RCHBr-CH R' BrBr + RO ROBrOverall, the reaction results in the anti-Markovnikov addition of HBr to the alkene, with the bromine atom attaching to the less substituted carbon and the hydrogen atom attaching to the more substituted carbon.