13.1 Properties of alkenes

• Naming Alkenes:

  • unsaturated hydrocarbons
  • suffix = ene
  • contain at least one carbon to carbon double bond in their structure
  • functional group = C=C
  • General formula = CnH2n
• The nature of the double bond:

  • each carbon has 4 electrons to form bonds
  • 3 of the 4 electrons are used in 3 sigma bonds
  • This leaves 1 electron on each carbon not involved in sigma bonds
  • the electrons are in p-orbitals
  • sideways overlap of 2 p-orbitals creates a pi bond
  • pi bond prevents free rotation around the bond
• pi bond - the sideways overlap of 2 p-orbitals
• The 3D shape around a double bond

  • 3 regions of electron density (2 single covalent bonds and 1 double covalent bond) around each carbon atom
  • These repel one another as far apart as possible
  • shape = trigonal planar
  • angle = 120