6.1.7 - Introduction to Mechanisms

• what are mechanisms?

  diagrams that break reactions down into individual stages to show how substances react together
• why are mechanisms used for organic reactions?

  when organic compounds react covalent bonds in molecules require energy to break b a sequence of bond breaking & making can happen as reactants turn into products
• why are mechanisms not used for ionic compounds?

  when ionic compounds react in solution it's almost instantaneous because ions simply collide
• curly arrows in mechanisms

  shams hom electron pairs more around

  points to where new bond is formed

  half arrow: 1 electron transferred

  full arrow: pair of electrons transferred
• ways in which a bond can break

  homolytically

  heterolytically
• homolytic fission

  when covalent bond is broken and each atom keeps one lectron producing a free radical which quickly reacts to form new products (free radical is an intermediate)

  bond breaks evenly
• where free radicals occur in homolytic fission

  reactions in the gas phase or in a non-polar solvent

  can be sped up using UV light
• heterolytic fission

  when covalent bond is broken & one atom gets both electrons while the other gets none producing ionic intermediates (nucleophiles and electrophiles)
• when does heterolytic fission happen?

  when reaction takes place in polar solvents
• what are reagents?

  compound or mixture added to a system to start or test a chemical reaction
• types of reagents

  nucleophiles

  electrophiles

  radicals
• what are nucleophiles?

  negatively changed ions or species with a lone pair of electrons

  they're electron rich (-) so are attracted to electron poor places (+) and donate electrons
• cwhat do nucleophiles do?

  attack molecules that have a partial positive charge
• reaction that involves nucleophiles

  substitution reaction of halogenoalkanes
• what are electrophiles?

  positively changed ions or species that are electron poor (have vacant orbital)

  electron loving
• what do electrophiles do?

  attack mobulbs that have a negative charge
• how do electrophiles form bonds?

  by accepting a pairf electrons from ion or molecule attacked during reaction
• what are radicals?

  o species with an unpaired electron formed by homolytic fission of covalent bonds
• Why are radicals very reactive?

  they have unpaired electrons I react with anything positive, negative or neutral
• types of reaction mechanisms

  free radical substitution/addition

  electrophilic addition/substitution

  nucleophilic addition/substitution

  elimination

  nucleophilic elimination