Alkenes Flashcards
What is an alkene?
An unsaturated hydrocarbon
What is a hydrocarbon?
A compound that contains only carbon and hydrogen
What is an unsaturated compound?
A compound that contains double bonds
What is the general formula for alkenes?
CnH2n
What type of isomerism can alkenes exhibit?
Geometric isomerism
What are stereoisomers?
Isomers that have the same molecular formulae but a different spatial arrangement of atoms
Why do alkenes exhibit geometric isomerism?
There is restricted rotation around the double bond
When does geometric isomerism arise?
it arises when:
- there is restricted rotation around the double bond
- there are two different groups atoms attached at both ends of the double bond
What is an electrophile?
A lone pair acceptor
What is an addition reaction?
A reaction where a molecule joins to an unsaturated molecule to form a saturated molecule
What is carbocation?
A positive ion with the positive charge on a carbon atom
Why are alkenes reactive?
There is a high electron density in the double bond
What types of bonds are in double covalent bond?
Pi and Sigma bonds
Why Pi bonds vulnerable to attack by electrophiles?
They are exposed and have a high electron density
What is an electrophile?
A lone pair acceptor
What can be used to test for unsaturation?
Bromine water
What happens when a solution is made containing an alkene and bromine water?
The solution decolourises
Orange to colourless
Why does bromine water decolourise the solution?
The Br atom is added onto the double bond by electrophilic addition
What is formed when alkenes react with hydrogen halide?
Halogenalkanes
What happens when hydrogen halides are added onto unsymmetrical alkenes?
Two products are produced
Major and minor
What determines the atom economy of each product formed?
The stability of the carbocation intermediate determines the atom economy of each product
What is an alkyl?
Alkanes with a hydrogen removed
What happens when there are more alkyl groups around a carbocation?
The carbocation becomes more stable because there are more alkyl groups feeding electrons towards the positive charge
What is the stability of a primary carbocation?
Least stable
What is the stability of a tertiary carbocation?
Most stable
What is formed when alkenes react with cold, concentrated sulfuric acid?
Alkyl hydrogensulfates
What is formed when water is added to the alkyl hydrogensulfate in warm conditions?
An alcohol is formed
Alkyl hydrogensulfates are formed through what type of reaction?
Electrophilic addition
An alcohol is formed through what type of reaction?
Hydrolysis
What is hydrolysis reaction?
A reaction where a molecule is split by the addition of water
What is the purpose of the sulfuric acid in the reaction?
It is a catalyst because it is regenerated
What is a polymer?
A long chained molecule formed from lots of repeated molecules joined together
What is a monomer?
A small molecule repeated many times making a polymer
Give examples of polymers
DNA
Proteins
Synthetics
What is an addition polymer?
A polymer made from alkenes when they act as monomers because their double bonds open up joining together to long chains
What are the properties of polyalkanes?
Unreactive
Non-polar
Saturated
Why are polyalkanes unreactive?
The C-C and C-H bonds are strong
What are the properties of long,straight chains?
Rigid
Strong
What are the properties of short, branched chains?
Flexible
Weak
What happens as the length of the chains increases?
The longer the polymer chains, the closer together they can get and the stronger the van der Waals forces between the chains
How can polymers be modified?
They can be modified using plasticisers which makes them more flexible
How do plasticisers make polymers more flexible?
The plasticiser molecules get between the polymer chains and push them apart
The intermolecular forces between the chains weaken
Therefore, the chains slide more making the polymer easy to bend
What is PVC formed from?
Chloroethene
What are the properties of rigid PVC?
Long, closely packed polymer chains
Hard
Brittle
What is rigid PVC be used for?
Drainpipes
Window frames
What are the properties of plasticised PVC?
Flexible compared to rigid PVC
What is plasticised PVC used for?
Electrical cable insulation
Flooring tiles
Clothing
