When an unsymmetrical alkene like propene reacts with $\text{HBr}$ in the presence of a peroxide, the addition takes place contrary to Markovnikov's rule. This phenomenon is known as the peroxide effect, Kharash effect, or anti-Markovnikov addition . The reaction proceeds via a free radical chain mechanism, resulting in the attachment of the bromide radical to the doubly bonded carbon atom that possesses more hydrogen atoms. Consequently, the major product formed is 1-bromopropane ($\text{CH}_3\text{-CH}_2\text{-CH}_2\text{Br}$), which is commonly known as n-propyl bromide .