Intro to reaction mechanisms

• Covalent bonds can be broken by either homolytic fission or heterolytic fission.
• Homolytic fission

  When a covalent bond breaks by a homolytic fission each of the bonded atoms takes one of the shared pair of electrons from the bond.

  Each atom now has a single unpaired electron so it is now a radical.
• Heterolytic fission

  When a covalent bond breaks by heterolytic fission one of the bonded atoms takes both of the electrons from the bond.

  • the atom that takes both electrons becomes a negative ion
  • the atom that does not take the electrons becomes a positive ion.
• Curly arrows are used to show the movement of electron pairs when bonds are being broken or made.
• There are three types of reactions:

  1. addition
  2. substitution
  3. elimination
• In an addition reaction, two reactants join together to form one product.
• In a substitution reaction, an atom or group of atoms is replaced by a different atom or group of atoms.
• An elimination reaction involves the removal of a small molecule from a larger one.