Introduction to reaction mechanisms

• How can covalent bonds be broken?

  homolytic fission or heterolytic fission
• What is homolytic 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 has a single unpaired electron

  an atom or groups of atoms with an unpaired electron is called a radical
• What is 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
• What do curly arrows show?

  the movement of electron pairs when bonds are being broken or made
• What happens in an addition reaction?

  two reactants join together to form one product

  e.g. a molecule is added to an unsaturated alkene, breaking the double bond to form a single. saturated compound
• What happens in a substitution reaction?

  an atom or group of atoms is replaced by a different atom or group of atoms
• What happens in an elimination reaction?

  an elimination reaction involves the removal of a small molecule from a larger one. In an elimination reaction, one reactant molecule forms 2 products