Alkenes are unsaturated hydrocarbons that contain at least one C=C bond made up of a sigma bond and a pi bond.
The general formula fro alkenes is CnH2n
A pi bond is formed when electrons in the adjacentporbitaldirectlyoverlapsideways, both above and below the carbon atoms.
The pi bond restricts rotation of carbon atoms
The angle and shape of a double bond is
Trigonal planar with a bond angle of 120 degrees
Alkenes are more reactive than alkanes because of the highelectron density of the doublebond and the pi bond is slightly easier to break
Alkenes only have london forces due to non-polar bonds
Alkenes are insoluble in water due to them being non-polar and water being polar
The equation for the complete combustion of pent-2-Ene is
C5H10 + 7 1/2 O2 ———> 5CO2 + 5H2O
Alkenes form two types of isomers
e/z isomers - due to restricted rotation
cis-trans isomers - if two of the same Substituents are attached to each carbon
Primary carbocations are the least stable and the carbon is attached to onecarbon chain.
Secondary carbocations are when the carbon is attached to twocarbon chains
Tertiary carbocations are the most stable and the carbon is attached to threecarbon chains
According to markownikoffs law:
When a hydrogen halide reacts with an unsymmetrical alkene, the hydrogen attaches to the carbon on the alkene with the most hydrogens and the least carbonchains.
The major product is formed from the moststable carbocation (usually a tertiary carbocation)
The minor product is formed from the least stable carbocation
the conditions needed for the electrophillic addition of H2O to an alkene is:
steam in the presence of an acid catalyst, usually phosphoric acid
reaction is called hydration
The products of a hydration reaction are an alcohol
This is the mechanism for the addition of water to ethene
This is the mechanism for HBr and ethene
When a halogen is added to an alkene the reaction is called halogenation
C=C double bonds interact with non-polar molecules as their highelectron density induces a temporary dipole in the halogen molecule making it §+ and the other molecules §- so the §+ molecule is attracted to the double bond
The reaction mechanism for the reaction of ethene with bromine is
An alkene is converted into an alkane in a reaction called hydrogenation.
hydrogen gas is added to make it a saturated hydrocarbon.
The conditions are temperatures above 150 degrees and a nickel catalyst
Addition polymers are many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule.
Monomers are molecules which combine to form a polymer.
They usually have a C=C bond which breaks to leave a repeatingpattern
Polymerisation of ethene is represented by this diagram
Plastics can be disposed by
landfill
combustion
electricity generation
reuse
recycle
organic feedstock
The disadvantages of recycling are
plastics must be sorted into different types
it can be expensive
it is labour intensive
required high technology
Photodegradable polymers break down chemically using energy with wavelengths similar to light.
Once the break down begins it is not possible to stop the process
In organic feedstock:
plastics are separated and broken down into small organic molecules through a series of reactions. The molecules can then be used to produce plastics and in other industries.
A disadvantage of photodegradable polymers is that they may not be exposed to sufficientlight