3.3.4 Alkenes Flashcards
Alkene definition
Unsaturated hydrocarbons
What is the bonding in alkenes
C=C, an area of high electron density making it susceptible to attacks from electrophiles
Electrophilic addition electrophiles
HBr
H2SO4
Br2
Test for alkenes
Bromine water/Br2
Goes from orange to colourless
Explain why there is attraction between Br2 and C=C
C=C bond has high electron density
Br-Br becomes polarised
∂+ Br attracted to C=C
Why is the major product more stable
It is formed by a more stable intermediate. Tertiary carbocations are the most stable as the positive charge is stabilised by three alkyl groups by positive inductive effect.
Most and least stable carbocations
Tertiary > Secondary > Primary
Propene repeating unit
. H H
- C - C -
. H CH3
What do plasticisers do to addition polymers
Make them more flexible
Why are addition polymers unreactive
Due to the strong saturated C-C bonds and C-H bonds. These are very difficult to break.
IMFs between polyalkenes
Long chains experience stronger intermolecular forces as they have more points of contact for IMFs
Straight chains experience stronger intermolecular forces as they pack closer together
Addition polymer production with higher pressure and temperature
Produces branched chains with weak IMFs
Addition polymer production with lower pressure and temperature
Produces straight chains with strong IMFs
Are polyalkenes sustainable
No as they are not biodegradable due to they unreactive saturated C-C bonds
PVC structure and properties
Polychloroethene has waterproof properties caused by addition of plasticisers in the reaction
