Alkenes

• Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond, making them susceptible to attack from electrophiles.
• Alkenes consist of a normal covalent bond and a π bond.
• Bromine water is used to identify this double bond and other unsaturated compounds, turning the solution from orange-brown to colourless if a double bond is present in the substance.
• Alkenes undergo electrophilic addition about the double bond, with electrophiles being electron acceptors that are attracted to areas of high electron density.
• Some of the most common electrophiles are HBr, Br2, H2SO4.
• Electrophilic addition is the reaction mechanism that shows how electrophiles attack the double bond in alkenes, forming a carbocation when the double bond is broken.
• The more stable the carbocation, the more likely it is to form, meaning in an addition reaction, multiple products can form but the major product will always be the most stable possible.
• The π bond causes the bromine molecule to gain a temporary dipole so that electrons are transferred.
• Alkene reacts with sulphuric acid to produce ethyl hydrogensulphate.
• Addition polymers are produced from alkenes where the double bond is broken to form a repeating unit.
• The reaction conditions used in the production of these polymer chains can be altered to give the plastics produced different properties.
• High pressures and temperatures produce branched chain polymers with weak intermolecular forces, whereas lower pressures and temperatures produce straight chain polymers with strong intermolecular forces.
• Polymers are unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds, making them useful for manufacturing many everyday plastic products such as shopping bags (poly(ethene)).
• The unreactive nature of the bonds in addition polymers means they are not biodegradable and cannot be broken down by species in nature.
• Poly(chloroethene) more commonly known as PVC is an addition polymer with waterproof properties, gaining these properties by the addition of plasticisers during the reaction.