Define kharasch effect.

Kharasch effect was first explained by Morris Selig Karasch. It is also known as the peroxide effect.

Kharasch effect

The addition of HBr (but not of HCl or HI) to unsymmetrical alkenes in the presence of peroxides such as benzoyl peroxide takes place contrary to Markovnikov’s rule. This effect is known as the Kharasch effect.

Example:

CH3CH2CH=CH+ HBr → CH3CH2CH3CH2Br

  • Anti Markovnikov addition also referred to as the Kharasch effect is an example of the addition reaction of alkenes which is an exception to Markovnikov’s rule.
  • Markovnikov’s rule: The rule states that, with the addition of a Protic acid HX (X=Cl, Br, I) to an asymmetric alkene, the acid hydrogen (H) gets attached to the carbon with more hydrogen substituents and the halide (X) group gets attached to the carbon with more alkyl substituents.

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