Question

Explain with a suitable example of the peroxide effect.

Write short notes on the Kharasch effect.

Answer 1

The peroxide effect (or Kharasch effect) occurs when HBr adds to an alkene in the presence of peroxides (H₂O₂), leading to anti-Markovnikov addition; the bromine atom attaches to the carbon with more hydrogen atoms, opposite to the usual Markovnikov rule. This effect happens via a free radical mechanism.

An example of peroxide is the addition of HBr to propene:

1. Reaction without peroxide (Markovnikov):
   \[\ce{\underset{propene}{CH3 - CH = CH2} + HBr -> \underset{2-bromopropane}{CH3 - CHBr - CH3}}\]
2. Reaction with peroxide (Anti-Markovnikov):
   \[\ce{\underset{propene}{CH3 - CH = CH2} + HBr ->[peroxide][] \underset{1-bromopropane}{CH3 - CH2 - CH3}}\]