4.1.3 Alkenes Flashcards
When is a sigma bond formed in an alkene
its formed between two carbon atoms using the direct overlap of electrons clouds of the two atoms
Whens a pie bond formed?
Its formed by the electrons in the adjacent p-orbitals overlapping above and below the carbon atoms.
What does the pie bond do?
It holds the atoms in position by restricting rotation around the double bond.
What shape and bond angles do alkenes have?
Each of the electron densities repel by the same amount forming a bond angle of 120, which results in a trigonal planar shape.
Describe the reactivity in alkenes
Alkenes are more reactive thanks alkanes due to the pie bond as being on the outside of the double bond, the pie- electrons are more exposed than the electrons in the sigma bond therefore a pie bond readily breaks and the sigma bond remains intact when alkenes react
What is an electrophile?
Its an electron - pair acceptor
What is hydrogenation?
> Its an addition reaction in which hydrogen (H2) is added across c=c bond
At a temp of 150 & nickel catalyst
What is halogenation?
Its an addition reaction in which a halogen is added across a c=c bond - the alkene becomes saturated and a dihaloalkane is produced.
How does halogenation allow you to test for unsaturation?
> Bromine solutions/ idodine solution + saturated compound = no reaction
Bromine solutions/ idodine solution + unsaturated compound = decolorisation
What is addition of hydrogen halides?
This is an addition reaction in which a hydrogen halide is added across the c=c bond. This produces haloalkanes
What is hydration?
> Its an addition reaction between a gaseous alkene and steam - it is used in industry to make alcohols.
300 celius and 65 atm & H3PO4
uses of poly(ethane)
Plastic bags and bottles
uses of poly(chloroethene) / PVC
ELectrical cable insulation, pipes, bottles
Uses of poly(propene)
children toys, crates, ropes
uses of Poly(phenylethene/styrene)
packaging
