Propene reacts with HBr in the absence of peroxide (in the dark). The major product is

Without peroxide the addition is electrophilic. $\mathrm{H}{}^{+}$ adds to the terminal carbon to form the more stable secondary carbocation, which is captured by $\mathrm{Br}{}^{-}$. The product follows Markovnikov's rule: 2-bromopropane.