Alkenes Flashcards
What is an alkene?
An unsaturated hydrocarbon with a carbon carbon double bond
How can you make alkenes?
Cracking
Elimination of halogenoalkanes
What is the general formula for alkenes?
CnH2n
What is the test for unsaturation?
Bromine water makes alkenes go from orange to colourless
What causes E-Z isomerism?
Restricted rotation around the double bond
What is stereoisomerism?
When molecules have the same structural formula but the atoms/groups have a different arrangement in 3D space
What is EZ isomerism?
When molecules have the same structural formula but a different arrangement of atoms in 3D space around a double bond
What are isomers?
Molecules with the same molecular formula but a different structural formula
What is addition polymerisation?
When alkenes react together to form addition polymers
What is a monomer?
The unit which breaks its double bond and forms polymers
What is a polymer?
A long chain of repeating monomer units joined together
What are the two types of poly(ethene)
Low density poly(ethene) and high density poly(ethene)
What are the conditions under which LDPE is made?
200 degrees celcius, 120000kPa with little oxygen
Describe the structure of LDPE
Branched chains which don’t pack closely together and softens at temps below 100
What are the conditions under which HDPE is made?
60 degrees celcius, titanium chloride catalyst
Describe the structure of HDPE
Straight chains which can pack more tightly together. Softens at higher temperatures
What is PVC?
poly(chloroethane)
How is PVC made softer?
Plasticiser which makes it more flexible
What bonds hold monomers together?
Covalent bonds
What bonds hold polymer molecules together?
Van der Waals forces
What are the problems with polymers?
Not biodegradable, take years to decompose, platic liter can be ingested by animals, non-renewable oil and if incinerated it produces toxic CO2 gas
What are electrophiles?
Electron pair acceptors
Why do electrophiles attack double bonds?
Bc they’re areas of high electron density
In electrophilic addition with bromine, what are the conditions?
Alkenes
Bromine
Room temp
No light
In the electrophilic addition with hydrogen bromide, what are the conditions?
Heat under reflux, alkenes, phosphoric (V) acid catalyst and sodium halide
When can more than one product be formed from electrophilic addition?
When the alkene is unsymmetrical
What is the most stable product in any electrophilic addition and why?
The one with more alkyl groups attached, bc alkyl groups have a positive inductive effect which pushes electrons towards the carbocation and stabilises its charge
What is Markovnikov’s rule?
The hydrogen halide adds on so that the hydrogen atom adds to the carbon which already has the most hydrogens
What is a carbocation?
A species which contains a positive charge on the carbon atom
What is an addition reaction?
A reaction in which two molecules join together to make one larger molecule
What is heterolytic fission?
When a covalent bond break and both electrons in the bond move to one of the atoms
What are the conditions needed for the electrophilic addition with sulfuric acid?
concentrated sulfuric acid, alkene and room temp
What are the conditions needed in hydration?
Stean, pressures of 60atm and 600K and a concentrated strong acid catalyst
What is the functional group of alkenes?
C=C
What is uPVC used for?
Window and door frames and drainpipes
What is PVC used for?
Clothing and wellington boots
