Organic Chemistry/Introduction to reactions/Hydrohalogenation

A simple alkene undergoing hydrohalogenation

Alkenes are electron-rich. Just look at those electrons all clumped together in the carbon-carbon double bond. They act as Lewis bases (they give up electrons).

Hydrohalogenation follows Markovnikov's rule. That is, the carbon of the double bond that starts out more substituted receives the halogen (becomes more substituated) while the carbon of the double bond that starts out less substituted ends up with the hydrogen.

''He who has, gets: This is another alkene illustrating hydrohalogenation. Notice how the more highly substituated carbon ends up with the X-''

The H+ is attracted to the electron-rich double bond and adds first, on the carbon with more hydrogens, leaving the other carbon with a positive charge (a carbocation). Then the X- reacts with the carbocation.

Read about Vladimir Vasilevich Markovnikov on Wikipedia.