Chemistry Class 11 Chapter 13. Hydrocarbons | Page 11

CH3 CH3
C
H +
2 1
At Position
( 1 )
CH 3
CH3
C CH 3
Br
CH 3
CH
C
CH
3
CH2
3 ° more stable cation
3
Br Major Product
H + CH 3 Br CH3
CH CH 2
CH 3
CH3
1 ° less stable cation
At Position ( 2 )
CH CH2 Br
Minor Product
Peroxide effect or Kharasch ( Anti Markownikoff ’ s addition ): - In 1933 Kharasch and Mayo observed that when HBr is added to an unsymmetrical double bond in the presence of organic peroxide , the reaction take places opposite to the Markovnikov rule .
CH 3
CH CH 2
HBr
Peroxide
CH3 CH2 CH2Br
propyl bromide
Noted : - peroxide effect is applicable only to HBr and not to HF , HCl and HI . Addition of HF , HCl and HI takes place according to Markovnikov ’ s rule even in the presence of peroxide .