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
• 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
• Carbocations have varying stability, with tertiary being the most stable and primary the least
• In an addition reaction, the major product will be the most stable possible
• Lower pressures and temperatures produce straight chain polymers with strong intermolecular forces
• Addition polymers are not biodegradable and cannot be broken down by species in nature
• Testing for unsaturation


  Shake an alkene with orange bromine water, solution turns from orange to colourless.

  Bromine is added across the double bond to form a colourless dibromoalkane by electrophilic addition.
• Alkenes undergo electrophilic addition reactions with hydrogen halides to form halogenoalkanes

  
  

  If the hydrogen halide adds to an unsymmetrical alkene, there are two possible products.

  
  

  The amount of each product formed depends on how stable the carbocation formed in the middle reaction is- the carbocation intermediate.

  
  

  Carbocations with more alkyl groups are more stable because the alkyl groups feed electrons towards the positive charge. More stable carbocations are much more likely to form.