Explain the Anti-Markovnikov rule or peroxide effect (Kharasch effect) or free radical addition reaction with an example.

(N/A) The Kharasch effect or peroxide effect is observed in the addition of $HBr$ to unsymmetrical alkenes in the presence of organic peroxides.
Rule: In the presence of peroxide,the addition of $HBr$ to unsymmetrical alkenes (like propene) occurs contrary to the Markovnikov rule. This effect is specific to $HBr$ and is not observed with $HCl$ or $HI$.
Example: $CH_3-CH=CH_2 + HBr \xrightarrow{(C_6H_5CO)_2O_2} CH_3-CH_2-CH_2Br$ ($1$-bromopropane).
Mechanism:
Step $(i)$ Formation of phenyl free radical: $(C_6H_5CO)_2O_2$ $\rightarrow 2C_6H_5COO^{\bullet}$ $\rightarrow 2C_6H_5^{\bullet} + 2CO_2$.
Step $(ii)$ Formation of bromine free radical: $H-Br + C_6H_5^{\bullet} \rightarrow C_6H_6 + Br^{\bullet}$.
Step $(iii)$ Addition of $Br^{\bullet}$ to the alkene: $CH_3-CH=CH_2 + Br^{\bullet} \rightarrow CH_3-dot{C}H-CH_2Br$ (secondary free radical,which is more stable).
Step $(iv)$ Formation of product: $CH_3-dot{C}H-CH_2Br + H-Br \rightarrow CH_3-CH_2-CH_2Br + Br^{\bullet}$.
The stability of free radicals follows the order: $3^{\circ} > 2^{\circ} > 1^{\circ} > dot{C}H_3$.