Why can free-radical addition place bromine differently than electrophilic addition?

Free-radical addition can place bromine differently than electrophilic addition because the two processes follow distinct reaction mechanisms.1

In standard electrophilic addition, the reaction typically follows the Markovnikov rule, where the halogen attaches to the carbon atom with fewer hydrogen atoms. This is an ionic process.23

In contrast, free-radical addition—often initiated by the presence of peroxides—proceeds through a homolytic mechanism. In this pathway, the reagent undergoes homolytic fission to produce neutral radicals that sustain a chain process. This mechanism can result in an orientation of substituents that is the opposite of that found in electrophilic addition, a phenomenon known as anti-Markovnikov addition. The explanation for this difference, specifically why hydrogen bromide exhibits this reversed-order addition, was provided by Morris Selig Kharasch in 1933.142