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please explain to me in detail the mechanism of free radical addition in the presence of peroxides and in the absence of peroxides.

please explain to me in detail the mechanism of free radical addition in the presence of peroxides and in the absence of peroxides.


2 Answers

bhanuveer danduboyina
95 Points
9 years ago

Markovnikov's rule

The rule states that with the addition of a protic acid HX to an alkene, the acid hydrogen (H) becomes attached to the carbon with fewer alkyl substituents, and the halide (X) group becomes attached to the carbon with more alkyl substituents.


The chemical basis for Markovnikov's Rule is the formation of the most stable carbocation during the addition process. The addition of the hydrogen (in the form of a proton) to one carbon atom in the alkene creates a positive charge on the other carbon, forming a carbocation intermediate. The more substituted the carbocation (the more bonds it has to carbon or to electron-donating substituents) the more stable it is, due to induction and hyperconjugation. The major product of the addition reaction will be the one formed from the more stable intermediate.

Anti-Markovnikov rule

Mechanisms which avoid the carbocation intermediate may react through other mechanisms that are regioselective, against what Markovnikov's rule predicts, such as free radical addition. Such reactions are said to be anti-Markovnikov, since the halogen adds to the less substituted carbon, exactly the opposite of Markovnikov reaction. Again, like the positive charge, the radical is most stable when in the more substituted position


879 Points
9 years ago

The reaction is done at high pressures in the presence of a trace of oxygen as an initiator.

The function of the oxygen - chain initiation

The oxygen reacts with some of the ethene to give an organic peroxide. Organic peroxides are very reactive molecules containing oxygen-oxygen single bonds which are quite weak and which break easily to give free radicals.

You can short-cut the process by adding other organic peroxides directly to the ethene instead of using oxygen if you want to.

You don't need to worry about the exact formulae of the free radicals which start the reaction off - they vary depending on their source. For simplicity we give them a general formula: Ra

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