homolytic & heterolytic fission

• during an organic reaction, bonds in the reactant molecules are broken and bonds in the product molecules are made
• the process of bond breaking is called bond fission
• during bond fission, the electrons are redistributed between the two atoms involved and this can happen by either homolytic fission or heterolytic fission
• homolytic fission involves the breaking of a covalent bond to produce two free radicals (neutral radicals)
• in homolytic fission each atom in the bond leaves with one electron from the shared pair
• the free radicals produced by homolytic fission are highly reactive because the unpaired electrons tend to attack other species
• homolytic fission usually occurs when the bond is non-polar or very slightly polar
• in homolytic fission the bond will break evenly while in heterolytic fission the bond breaks unevenly
• reactions involving homolytic fission tend to result in the promotion of very complex mixtures of products, making them unsuitable for organic synthesis
• heterolytic fission occurs when a covalent bond breaks and both electrons in the bond move to one of the atoms
• heterolytic fission results in the formation of two oppositely charged ions
• heterolytic fission normally occurs when polar covalent bonds are broken
• reactions involving heterolytic fission tend to result in fewer products than reactions involving homolytic fission
• heterolytic fission is better suited for organic synthesis
• single headed arrow

  movement of a single electron
• double headed arrow

  movement of an electron pair
• arrow tail

  shows electron source
• arrow head

  shows electron destination
• two single headed arrows starting at the middle of a covalent bond

  homolytic fission is occurring
• a double headed arrow starting in the middle of a covalent bond

  heterolytic fission is occurring
• an arrow with the head pointing to the space between two atoms

  a covalent bond will be formed between the two atoms