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JEE Main levelSingle correct optionDifficulty 2 of 3g3128

The peroxide (anti-Markovnikov) effect is observed with $HBr$ but not with $HCl$ or $HI$ because

A $HCl$ and $HI$ are nonpolar
B $HBr$ has the weakest H-X bond of the three
Cperoxides cannot produce halogen radicals from $HCl$ or $HI$ at all
Donly for $HBr$ are both chain propagation steps energetically favourable

Answer: D

With

HCl

the step in which the alkyl radical abstracts H from

HCl

is endothermic, because the H-Cl bond is strong. With

HI

the addition of

I X^{∙}

to the alkene is endothermic. Only for

HBr

are both steps feasible. The weakest bond belongs to

HI

, not

HBr

.

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