(E)-1-Phenylpropene, $\mathrm{C}{}_6\mathrm{H}{}_5-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}{}_3$, is treated with HBr in the presence of peroxide. The major product is

$\mathrm{Br}\cdot$ adds to the carbon that leaves the more stable radical. Adding to C-2 gives the resonance-stabilised benzylic radical at C-1. H abstraction from HBr then gives $\mathrm{C}{}_6\mathrm{H}{}_5-\mathrm{CH}{}_2-\mathrm{CHBr}-\mathrm{CH}{}_3$, (2-bromopropyl)benzene. The ionic route would give (1-bromopropyl)benzene.