Reactions of alkenes

Electrophillic addition

A type of addition in which an electrophile ( electron pair acceptor) is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.

State the steps of halogenation of alkenes and draw diagrams

1. An induced dipole is formed at the halogen e.g. bromine, when they get closer to the double bond in the alkene. So the electrons in the bromine repel to one bromine atom of the element, which causes this induced dipole

2. The positively charged bromine of the halogen is then attracted to the electron dense double bond of the alkene, breaking the double bond and forming a new bond with the positive bromine

3. This then forms a carbocation as one of the carbons in the structure now only has 3 bonds around it meaning the the negative bromine which was left behind is then attracted to the carbocation

4. Forming the final product of 1,2-dibromoethane

Why is halogenation an electrophilic reaction

This reaction is electrophilic as the pi bond a region of high electron density and attracts the δ⁺ bromine molecule which acts as an electrophile. It is an addition reaction because the carbon double bond breaks and a new halogen carbon bond is formed

Hydrogenation of alkenes

Conditions for hydrogenation is a nickel catalyst, hydrogen and a temperature of 150^o

CH2​=CHBr+H2 ​⟶ ^Ni, 150 °C​CH3​−CH2​Br

Hydration of alkenes

Conditions needed are in the presence of steam, phosphoric acid and a temperature of around 300 °C

CH2​=CH2​+H2​O(g) ⟶CH3​CH2​OH