Question

Product of anti Markonikoffs rule with example

Answer 1

To understand anti-Markonikov's rule . We need to know what Markonikov's rule say:

Markonikov's Rule:

The addition of HBr to a symmetrical alkene yields only one product. Ex: When ethylene is reacted with HBr, it invariably yields ethyl bromide only.

But, the addition of HBr to a asymmetrical alkene yields 2 products. I will take the most simple asymmetrical as example, When propene is reacted with HBr it yields 1-bromopropane and 2-bromopropane. (The mechanism being electrophilic addition)

Now the question arises which one is major product among the two.

So, Markonikov's has observed these type of reactions and came up with this rule that- “Among the two the major product during the addition reaction will form in such a way that the negative part of addendum will add to the carbon containing least number of hydrogens”. Hence in the above reaction 2-bromo propane is the major product as the bromine is added to the carbon containing only one hydrogen.

Anti-Markonikov's Rule:

Imagine the same reaction taking place in the presence of free radical initiators like peroxides. Here, instead of electrophilic addition free radical addition occurs.

So coming back to the reaction of propene (asymmetrical alkene), the major product is 1-bromopropene and not 2-bromopropene. Since, the major product formed is just opposite to Markonikov's rule it is called Anti-Markonikov's Rule.

PS: Anti-Markovnikov addition is restricted to hydro halogenation and halogenation reactions alone, as free radicals cannot form in other type of additions.

Cheers!!