IB Chemistry Power Points                               Topic 20                          Organic Chemistrywww.pedagogics....
SN2 Nucleophilic Substitution - Review Recall: nucleophilic substitution of a bromoalkaneReaction occurs whenbromoethane i...
SN2 Reaction with Cyanide ionsBromoethane + CN- ions (KCN, reflux in methanol) - mechanismOverall
SN2 Reaction with Cyanide ionsProduct is a nitrile                       propanenitrile
SN2 Reaction with ammoniaBromoethane + NH3 (concentrated, pressure) - mechanismCation donates proton to another NH3
SN2 Reaction with ammoniaFor IB – The overall reaction is considered to be Product is also a nucleophile
2o and 3o amines are formed
Effect of nucleophile on rate ofsubstitutionThe electron density of the nucleophile affects the rate ofsubstitution.- Anio...
Effect of R-X on rate of substitutionRate of substitution is fastest when the leaving halide ionis iodine and slowest when...
Effect of R-X on rate of substitutionRate of substitution depends on whether thehalogenoalkane is primary, secondary or te...
Effect of nucleophile on rate ofsubstitutionThe concentration of the nucleophile affects the rate ofSN2 substitution but n...
Topic 20 2    substitution reactions
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Topic 20 2 substitution reactions

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Transcript of "Topic 20 2 substitution reactions"

  1. 1. IB Chemistry Power Points Topic 20 Organic Chemistrywww.pedagogics.ca Substitution Reactions
  2. 2. SN2 Nucleophilic Substitution - Review Recall: nucleophilic substitution of a bromoalkaneReaction occurs whenbromoethane is added to adilute NaOH solution.
  3. 3. SN2 Reaction with Cyanide ionsBromoethane + CN- ions (KCN, reflux in methanol) - mechanismOverall
  4. 4. SN2 Reaction with Cyanide ionsProduct is a nitrile propanenitrile
  5. 5. SN2 Reaction with ammoniaBromoethane + NH3 (concentrated, pressure) - mechanismCation donates proton to another NH3
  6. 6. SN2 Reaction with ammoniaFor IB – The overall reaction is considered to be Product is also a nucleophile
  7. 7. 2o and 3o amines are formed
  8. 8. Effect of nucleophile on rate ofsubstitutionThe electron density of the nucleophile affects the rate ofsubstitution.- Anions are more reactive than neutral molecules.Reactivity depends on how easily the nucleophile candonate electrons- N is less electronegative than O Rate of Reaction CN- > OH- > NH3 > H2O
  9. 9. Effect of R-X on rate of substitutionRate of substitution is fastest when the leaving halide ionis iodine and slowest when the leaving halide ion isfluorine. WHY?
  10. 10. Effect of R-X on rate of substitutionRate of substitution depends on whether thehalogenoalkane is primary, secondary or tertiary. 1o Rate of SN2 Rate of SN1 Reaction 2o Reaction Increases Increases 3o
  11. 11. Effect of nucleophile on rate ofsubstitutionThe concentration of the nucleophile affects the rate ofSN2 substitution but not SN1.

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