Markonikov Rule

In the last few examples you would have noticed that there are two possible products in each case.

The H of the hydrogen halide (or water) may add on to the carbon of CH ₂ or CH leading to two different products.

The one that is actually formed may be predicted using “Markovnikov’s rule” which is stated as follows:

In the addition of hydrogen halides to unsymmetrical alkenes the hydrogen adds on to the least substituted carbon ( the carbon which has more hydrogens attached to it).

From the mechanistic perspective the rule is stated as follows.

In additions to unsymmetrical alkenes the positive part of the addendum adds on to such a carbon so that the reaction goes through a more stable carbocation.

Exception to Markonikov Rule

Also known as Anti Markonikov rule or peroxide effect

When HBr adds on to an alkene in the presrnce of an organic peroxide the other product is formed, that is the hydrogen adds on to the most substituted carbon.