Alkenes - Electrophilic Addition Reaction

Alkenes react with halogen molecule via an Electrophilic additon mechanism. First, we need to define an electrophile. An electrophile can be defined as a species which is electron deficient which has the ability to accept a pair of electrons.

Therefore, in the mechansim there must be an electrophile that starts the reaction. The halogen molecule in the reaction between alkene and halogen is the electrophile.

In addition, there are three possible medium where the halogen molecule may be used. In this example, I will be using the reaction between ethene and bromine to illustrate the electrophilic addition mechanism.

When ethene reacts with Br₂ which is dissolved in CCl₄. The following picture describes the mechanism.

When ethene reacts with Br₂ which is dissolved in H₂O, Br₂ is still the electrophile that reacts with the alkene. The following picture describes the mechanism.

However, when ethene reacts with Br₂ which is dissolved in NaCl solution, the following picture describes the mechanism. Again, Br₂ is the electrophile which reacts with the alkene

In conclusion, the following video helps to explain "how to describe electrophilic addition reaction" questions.

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^{Article written by Kwok YL 2009.}

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