Anti Markovnikov’s rule or Kharasch effect or peroxide effect-
The addition of any polar molecule(HBr) to any unsymmetrical alkene
(propene)
in the presence of
benzoyl peroxide
takes place against the Markovnikov’s rule
According to this rule –
When any polar
molecule is added to any unsymmetrical alkene in
presence of any organic peroxide,
the negative part of molecule is added to that
carbon atom which is connected to more Hydrogen atom
than the other unsaturated carbon atom which is connected to less
Hydrogen atom and positive part attached
which carries lesser number hydrogen
. this is called Anti
-Markovnikov’s rule or Kharasch effect or peroxide effect
Morris selig kharasch and
mayo 1933 explained this process for first time addition of HBr
to unsymmetrical alkene than its called kharasch
effect
Mechanism of Anti
Markovnikov addition
Anti Markovnikov addition reaction is follow a free radical mechanism.
The
peroxide compound involved helps in the generation of free radicals(formation of stable secondary free radical). A general
mechanism of anti-Markovnikov addition reaction is discussed below:
- (A) STEP –I
Generation of free radical through homolytic cleavage of peroxide
compound.
(B) STEP - II Attack of generated free radical on Hydrogen Bromide
to form Bromide free radical through homolytic fission
