3. Alkenes

• Alkenes are unsaturated hydrocarbons meaning they contain a carbon-carbon double bond
• The C-C double bond is an area of high electron density making it susceptible to attack from electrophiles
• Alkenes undergo electrophilic addition about the double bond
• Common electrophiles are:

  HBr

  Br2

  H2SO4
• Electrophiles are electron acceptors and are attracted to areas of high electron density
• Electrophilic addition shows how electrophiles attack the double bond in alkenes
• When the double bond is broken, a carbocation forms

  • A carbon atom with only three bonds, meaning it has a positive charge
• Carbocations can have varying stability - tertiary being most stable and primary the least
• The more stable the carbocation, the more likely it is to form
• In an addition reaction, multiple products can form but the major product will always be the most stable possible
• Addition polymers are produced from alkenes where the double bond is broken to form a repeating unit
• Why is there no rotation about the C-C double bond?

  Due to the pi orbital - electron density above and below the single bond which holds the carbon atoms in place
• > Reaction conditions

  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

  > Lower pressures and temperatures produce straight chain polymers with strong intermolecular forces
• label the atoms for the structure of sulfuric acidddd H2SO4

  A) O

  B) OH

  C) O

  D) HO

  E) S

  
• A compound is the major product due to more stable carbocation which is (primary/secondary/tertiary)
• There is still concern about ozone depletion because:

  • CFCs take many years to reach the ozone layer OR long residence time
  • CFCs are still being used
  • There are other ozone depleting substances
• The addition of a water molecule to a compound is known as hydration