Alkenes
CnH2n/ Unsaturated hydrocarbons: Contain C=C and are made of only C and H
C=C contain a pi and sigma bond, is a region of high electron density, open to attack by
electrophiles, much more reactive than alkanes.
A sigma bond is formed by the linear overlap of two S-orbitals, free rotation
A sigma bond can also be formed by the linear overlap of S and P
Pi bond is formed by the sideways overlap between two p orbitals
Reactions
Bromination of Ethene:
Electrophilic Addition
C2H4 + HBr → C2H5Br
Primary Carbocation: Carbocation which has one carbon directly attached to the positively
charged carbon
Two possible options, tertiary carbocation is most stable, most formed.
Hydrogenation:
Finely divided nickel catalyst, 180oc, 4atm
C2H4 + H2 → C2H6
Hydration:
Conc. phosphoric acid, 300oc, 60atm
C2H4 + H20 →C2H50H
Bromination with Bromine Water
-Mix Bromine Water with a liquid alkene or bubble a gaseous alkene through bromine water
-C2H4 + Br2 → C2H4Br2
Test for a C=C bond
If yellow bromine water changes to colourless in the presence of an organic compound =
contains a C=C
Polymerisation: Joining together of small molecules to form a larger molecule
CnH2n/ Unsaturated hydrocarbons: Contain C=C and are made of only C and H
C=C contain a pi and sigma bond, is a region of high electron density, open to attack by
electrophiles, much more reactive than alkanes.
A sigma bond is formed by the linear overlap of two S-orbitals, free rotation
A sigma bond can also be formed by the linear overlap of S and P
Pi bond is formed by the sideways overlap between two p orbitals
Reactions
Bromination of Ethene:
Electrophilic Addition
C2H4 + HBr → C2H5Br
Primary Carbocation: Carbocation which has one carbon directly attached to the positively
charged carbon
Two possible options, tertiary carbocation is most stable, most formed.
Hydrogenation:
Finely divided nickel catalyst, 180oc, 4atm
C2H4 + H2 → C2H6
Hydration:
Conc. phosphoric acid, 300oc, 60atm
C2H4 + H20 →C2H50H
Bromination with Bromine Water
-Mix Bromine Water with a liquid alkene or bubble a gaseous alkene through bromine water
-C2H4 + Br2 → C2H4Br2
Test for a C=C bond
If yellow bromine water changes to colourless in the presence of an organic compound =
contains a C=C
Polymerisation: Joining together of small molecules to form a larger molecule
