Chapter 13

• Define an alkene?


  An unsaturated hydrocarbon (C-C double bonds)

  General formula = CnH2n
• What is the nature of the double bonds?

  They cannot be next to each other directly

  Each carbon atom has 4 electrons to form bonds

  3/4 electrons are used in the three sigma bonds

  Sideways overlap of p-orbitals create a Pi bond
• What does a Pi bond do?

  Restrict the rotation around the C-C double bond
• What is the 3D shape of an alkene?

  Trigonal planar

  This is because electron pairs repel as far apart as possible from each other
• Define stereoisomerism?


  Compounds which have the same structural formula but different arrangement of atoms in 3D shape - optiral isomerism, E/Z isomerism
• What are the feature of E/Z isomerism?

  Compounds must contain C-C double bond (presence of Pi bond)

  Two different groups must be attached to each C of the C-C double bond
• How do you determine which isomerism it is?

  Atomic number based priority
• What is trans - isomerism?


  across the double bond
• What is cis - isomerism?

  on the same side of the double bond
• What happens in hydrogenation of alkenes?

  Hydrogen (H2) reacts in presence of a nickel catalyst.