Why are alkenes more reactive than alkanes?
Due to the C=C double bond - region of high electron density so attracts electrophiles
What is a pi bond?
Sideways overlap of p-orbitals above & below the sigma bond
What is stereoisomerism?
same structural formula but different arrangement in space
What are the 2 types of stereoisomerism?
- Geometric isomerism (Alkenes only)
- Optical isomerism
What is geometric isomerism?
When there is a C=C double bond and 2 different groups are bonded to each C atom in the C=C
Known as EZ isomerism
Result of the restricted rotation around the C=C
Define E & Z isomerism
- Z - same priority groups are on the same side
- E - same priority groups on opposite sides
What is meant by a priority group?
Atom on each carbon with the highest atomic no.
specifically when 2 different groups are present
What are the 4 addition reactions of alkenes you need to know?
- Hydrogenation - addition of hydrogen (Ni catalyst required)
- Halogenation - addition of a halogen
- Addition of an acid - HCl or HBr
- Hydration - addition of water (temp equal to or above 100 degrees, H2SO4 or H3PO4 catalyst)
Acid HAS to be CONCENTRATED
What is an electrophile?
Electron pair acceptor
What type of fission occurs in electrophilic addition mechanism?
Heterolytic fission
What is the test for alkenes?
Bubble in bromine water - orange colour is decolourised
How can a non-polar molecule posess partial charges?
Electron rich area of the double bond in the alkene induces a diople
Electrons repel so the molecule becomes polar
What is formed when an alkene is unsymmetrical?
2 different products formed - major & minor product
They give 2 diff carbocation intermediates
How is the major product formed?
Via the more stable carbocation
What is meant by the stability of a carbocation?
- Primary(1”) - 1 alkyl group directly bonded
- Secondary(2”) - 2 alkyl groups directly bonded
- Tertiary(3”) - 3 alkyl groups directly bonded
most stable forms the major product & least stable froms the minor
Primary the least stable, Tertiary the most stable
What is addition polymerisation?
Joining together many small molecules, monomers (alkenes), to form a very large molecule, a polymer (polyalkenes), which are unreactive
What are plasticisers?
Other compounds added to addition polymers to make the plastic more flexible
e.g. cling film
What is the main issue with addition polymers?
They are non-biodegradeable - they cannot be hydrolysed
How can we prevent sending addition polymers to landfill?
- Recycling
- Use as an organic feedstock
- Combust in the production of energy
What are the advantages & disadvantages of recycling?
- A - do not have to send polymers to landfill, reduces requirement for new polymers to be made
- D - expensive to sort, not possible for all plastics
What are the advantages & disadvantages of organic feedstock?
- A - does not go to landfill, reduces the need to use non-renewable resources, reduces the need for cracking crude oil
- D - none
waste polymers converted into other chemicals used in chemical manufacturing processes
What are the advantages & disadvantages of combustion in production of energy?
- A - does not go to landfill, reduces need to combust fossil fuels
- D - releases CO2 contributing to global warming, HCl or CO can be produced
ensure plenty of O2 to avoid incomplete combustion
How can you prevent HCl or CO being produced during combustion?
- HCl gas can be prevented from entering the atmosphere by reacting it with bases (e.g. CaCO3 or CaO) to neutralise it
- Ensure plenty of O2 to avoid incomplete combustion so CO is not produced
What are the advantages of making polymers from renewable resources?
- Reduces the dependency on non-renewable resources e.g. crude oil
- Biodegradeable - naturally broken down by bacteria
- Photo degradeable - naturally broken down by sunlight
can be made from corn strach or other foods
