How many of the following hydrogen halides exhibit the peroxide effect (anti-Markovnikov free radica — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

The peroxide effect requires both steps of the free radical chain propagation to be exothermic. This condition is exclusively met by $HBr$. The $H-F$ and $H-Cl$ bonds are too strong for the carbon radical to abstract a hydrogen atom exothermically. The iodine free radical ($I^\cdot$) from $HI$ is too stable and sluggish to exothermically attack the alkene double bond, preferring to dimerize into $I_2$. Thus, only 1 hydrogen halide ($HBr$) shows the effect.