How can I illustrate antimarkovnikov's rule by the addition of hydrogen bromide to propene in the presence of benzoyl peroxide?

1 Answer
Jun 13, 2015


You write the mechanism for the reaction.


This is a free radical reaction, so it has initiation, propagation, and termination steps.


The chain is initiated by free radicals produced by cleavage of an #"O-O"# bond in the benzoyl peroxide.

The benzoyl radicals extract a hydrogen atom from an #"HBr"# molecule to produce bromine radicals.

#"PhCOO·" + "H-Br" →"PhCOOH" + "·Br"#


The bromine radical adds to the propene to form the more stable 2° radical.

The 2° radical reacts with another HBr molecule to produce 1-bromopropane and a bromine radical to continue the process.


Eventually two free radicals hit each other and produce a molecule of some sort.

#"Br·" + "·Br" → "Br"_2#

#"CH"_3"-" stackrel(·)("C")"H-CH"_2 "-Br" + "·Br" → "CH"_3"-CHBr-CH"_2"-Br"#

#"2CH"_3"-" stackrel(·)("C")"H-CH"_2 "-Br" → "Br-CH"_2"-CH(CH"_3")-CH(CH"_3")-CH"_2"-Br"#

The process stops here because no new free radicals are formed.