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In the presence of peroxide addition of ...

In the presence of peroxide addition of HBr to propene takes place according to anti Markownikoff's rule but peroxide effect is not seen in the case of HCl and HI. Explain.

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`underset("propene")(CH_(3)-CH=CH_(2)+HBr)overset("Perioxide")rarrunderset("n-propyl bormide")(CH_(3)-CH_(2)CH_(2)Br)`
The mechanism of the reaction is

Perioxide effect is effective only in the case of HBr and not seen in the case of HCl and HI. This is due to the following reasons.
(i) H - Cl bond (103 kcal/mol) is stronger than H-Br bond (87 kcal/mol) H-Cl bond is not decomposed by the peroxide free redical whereas the H-I bond is weaker (71 kcal/mol) form iodine free radicals .
(ii) lodine free radical `(I^(@))` formed as H - I bond is weaker bot iodine free radicalts readily combine with each other to form iodine molecules rather attacking the double bond .
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