Alkenes- electrophillic addition

An electrophile is an electron pair acceptor

• Mechanism for the reaction between ethene and Bromine.The halogen adds across the double bond.

balanced equation: C2H4 + Br2 ---->C2H4Br2

Alkenes react in the cold with pure liquid bromine, or with a solution of bromine in an organic solvent like tetrachloromethane. The double bond breaks, and a bromine atom becomes attached to each carbon. The bromine loses its original red-brown colour to give a colourless liquid. In the case of the reaction with ethene, 1,2-dibromoethane is formed.

When Br2 approaches,the Br--Br bond becomes polar. A pair of electrons flow from the double bond to the slightly positive Cl and a bond is formed.

A nucleophile attacks and electron deficient carbon atom of group and donates its electron pair.

halogenoalkanes take part with nucleophiles like (OH-) or H2O

Aqueous Hydroxide ions OH- react with chloromethanein a nucleophilic substitution reaction.

The nucleophilic OH- attacks the back of the carbon atom donating an electron pair.  A new bond is formed and the carbon-halogen bond breaks