Mechanisms

• Define free radical

  • A reactive species containing an unpaired electron
  • E.g.Cl-
• Define nucleophile

  • Electron pair donors
  • E.g. :-OH :-CN :NH3
• Define electrophile

  • Electron pair acceptor
  • E.g. H+
• What are the 3 types of reaction

  • Substitution
  • Addition
  • Elimination
• What are the 3 steps involved in free radical substitution?

  • Initiation
  • Propagation
  • Termination
• What do you need for free radical substitution to occur? What does it produce?

  • Halide + UV light
  • Alkane -> haloalkane
• Why is UV light required for free radical substitution to occur?

  It provides energy to break the halide-halide bond (Cl-Cl)
• When would the mechanism be electrophiluc addition

  • HBr
  • Br2
  • H2SO4
• Why does electrophilic addition produce a major and minor product?

  • It depends on the stability of the carbocation
  • Tertiary > Secondary > Primary
  • More stable = more likely to form
• When would the mechanism be nueophilic subsitution? And what does it produce?

  • Aqueous NaOH or KOH -> alcohol
  • Ethanolic KCN -> nitrile
  • Ethanolic NH3 -> amine
• When would the mechanism be elimination? And what does it produce

  • Haloalkane and ethanolic NaOH or KOH
  • Makes an alkene
• Why does an elimination mechanism produce multiple different products?

  It depends on which H+ is attacked as to where the double bond forms and therefor the alkene which does also
• Why do hydration and elimination reactions uses concentrated acid catalysts? Give an example of a catalyst used

  • Acid provides H+ ions which are required for the 1st step of the mechanism
  • The H+ ions are then regenerated in the final step
  • Concentrated H2SO4 or H3PO4
• When would a electrophilic subsitution occur?

  • Nitration of benzene - with NO2+
  • Friedel-Crafts acylation - using CH3CO+
• Give equation of HNO3 and H2SO4 reacting to produce NO2+

  HNO3 + H2SO4 -> HSO4- + H2NO3+

  H2NO3+ -> NO2+ + H20
• Why does nucleophilic addition lead to the formation of optical isomers?

  Nucleophile can attack from above or Bellow the plane, forming 2 different isomers
• When would nucleophilic addition-elimination occur?

  • With H2O -> carboxylic acid
  • With alcohols -> esters
  • With NH3 -> amide
  • With amine -> forms N-Substituted amide