intro to reaction mechanisms

• Covalent bonds can either be broken by homolytic fission or heterolytic fission
• When a covalent bond breaks by 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
  • an atom or group of atoms with an unpaired electron is called a radical
• 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
• The reaction mechanism is the process by which the reaction takes place
• In a reaction mechanism, curly arrows are used to show the movement of electron pairs when bonds are being broken or made
• 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. In an elimination reaction, one reactant molecule forms two products. E.g the elimination of water from an alcohol