Answer to Question #71270 in Organic Chemistry for umesh rai

Question

WHY DOES ONLY HBr give anti anrkownikovs product in presence of per oxide among all the halo acid

Answer 1

Because only HBr produces a Br-radical (in presence of peroxide), which then reacts with the double bond. It is considered that HF and HCl are too stable to produce free radicals. HI produces I-radicals, but they have not enough activity for starting of radical chain reaction.
This is also known as “the peroxide effect” or “the Kharasch effect”.