Concept:
Addition of HBr in presence of peroxide follows anti-Markovnikov rule through free radical mechanism.
Step 1: Understanding peroxide effect.
In presence of benzoyl peroxide:
\[
HBr
\]
adds via free radical pathway.
Bromine radical attacks the double bond first.
Step 2: Stability of radical intermediate.
If bromine adds to terminal carbon:
\[
\text{benzylic radical forms}
\]
Benzylic radicals are highly stable due to resonance.
Therefore bromine attaches to the carbon farther from benzene ring.
Step 3: Final product formation.
Hydrogen attaches to benzylic carbon and bromine attaches to adjacent carbon.
Thus product formed is:
\[
HO-C_6H_4-CH_2-CH(Br)-CH_3
\]
