Alkenes

• Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond
• The double bond area has high electron density and is susceptible to attack from electrophiles
• Example: Bromine water turns orange-brown to colourless in the presence of a double bond
• Alkenes undergo electrophilic addition around the double bond
• Electrophiles are electron acceptors attracted to areas of high electron density
• Common electrophiles include HBr, Br2, and H2SO4
• Electrophilic addition reaction mechanism involves the formation of a carbocation when the double bond is broken
• Carbocations can vary in stability, with tertiary being the most stable and primary the least
• The major product in an addition reaction will be the most stable carbocation possible
• Addition polymers are produced from alkenes by breaking the double bond to form a repeating unit
• Repeating units must be shown with extended bonds through brackets to indicate bonding to other repeating units on both sides
• Reaction conditions can be altered to produce polymers with different properties
• High pressures and temperatures produce branched chain polymers with weak intermolecular forces, while lower pressures and temperatures produce straight chain polymers with strong intermolecular forces
• Polymers are unreactive hydrocarbon chains with multiple strong, non-polar covalent bonds
• Uses of polymers include manufacturing everyday plastic products like shopping bags (poly(ethene))
• PVC (Poly(chloroethene)) is an addition polymer with waterproof properties
• Plasticisers are added during the reaction to give PVC its waterproof properties