3.3.4 Alkenes Flashcards
what is the general formula of an alkene?
CnH2n
What is an alkene?
Unsaturated hydrocarbon
C=C double bond
Why is there no rotation around the C=C double bond?
Electron density above and below holds the carbon atoms in place
Are alkenes more or less reactive than alkanes? Why?
More reactive due to high electron density of the double bond and the pi bond is slightly easier to break
What intermolecular forces do alkenes have?
Only Van der Waals
(Non polar bonds)
Are alkenes soluble in water? Why?
No
No polar bonds
Cannot form H bonds with water molecules, the hydrogen bonding within water is stronger
Name the three types of isomer alkenes can form?
positional isomer
chain isomer
E/Z
Write an equation for the complete combustion of pent-2-ene.
C5H10 + 7.5O2 —> 5CO2 + 5H2O
What is an electrophile?
Electron deficient atoms/ions which accept a pair of electrons (here, from the C=C bond)
What is the most stable type of carbocation intermediate?
The one bonded to the most other carbon atoms eg. Tertiary carbocation
Major products will be formed from which kinds of carbocation?
Tertiary
What conditions are needed for the electrophilic addition of H2O to an alkene?
Acid catalyst
What are the products of electrophilic addition of H2O to an alkene?
An alcohol
What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?
Room temperature
What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?
Room temperature and organic solvent
How does a molecule with a non-polar bond react as if it is an electrophile?
C=C double bond with a high electron density induces a temporary dipole in the halogen molecule
What is an addition polymer?
Many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule
What are monomers? What form do they usually take?
Molecules which combine to form a polymer
Usually have a C=C double bond which breaks to leave a repeating pattern
Give 3 uses of poly(chloroethene) / PVC?
Drainpipes
Vinyl
Aprons
What are plasticisers?
Small molecules that get between polymer chains to force them apart so they can slide over each other.
How does the physical properties of PVC change due to a plasticiser? What can this be used for?
Makes PVC more flexible
With plasticiser - aprons
Without plasticiser - drainpipes
Why do molecules containing mainly C-C and C-H bonds not decompose easily?
Bonds are non-polar so are not attacked by enzymes
Why is a lack of biodegradability in compounds with C-C or C-H bonds a problem?
Disposal is very problematic
