3.3.4 alkenes

• why do Z isomers have higher BPs than E isomers?

  Z isomers have larger dipole-dipole forces and increased points of interaction
• why do E isomers have higher MPs than Z isomers?

  E isomers pack closer together in a solid
• geometrical isomerism occurs due to limited rotation around the C double bond
• electrophile: an electron pair acceptor
• the electron rich double bond in alkenes is attracted to the delta positive atom found in an electrophile
• 3 examples of electrophiles:

  • Br2
  • HBr
  • H2SO4
• what is the reagent used to test for alkenes?

  Bromine water
• what are the observations for testing for an alkene?

  orange solution ——> colourless solution
• addition: two molecules forming one molecule
• electrophilic addition occurs in alkenes
• carbocation: positively charged carbon
• a tertiary carbocation is the most stable carbocation
• a primary carbocation is the least stable carbocation
• a major product is formed from a tertiary/secondary carbocation intermediate which is more stable than a secondary/primary carbocation intermediate due to a greater positive inductive effect
• exam hint: to form a major product in a mechanism add the H to the C with the most H already attached to it