第六章常见反应机理课件

Chapter6Familiarreactionmechanisms1.ARadicalChainMechanism2.ElectrophilicadditiontoC,Cmultiple

bonds3.NucleophilicadditiontoC,Cmultiple

bonds4.ConcertedadditiontoC,Cmultiplebonds5.Substitutionreactions6.Eliminationreactions7.NamereactionsStep1:Chaininitiation:

formationofradicalsfromnonradicalspeciesStep2:Step3:Chainpropagation:

reactionofradicalsandamoleculestoformanewradical1.1Alkanehalogenationreaction1.ARadicalChainMechanismChaintermination(Destructionofradicals):

DisproportionationCouplingBonddissociationenergy(kJ/mol)Enthalpychange△H?Entropychange△S?Freeenergychange△G?Howaboutthechlorinationofmethane?Howaboutthebrominationofpropene?Activity:F>Cl>Br>I;Allyl,3°>2°>1°Selectivity:F<Cl<Br<I;Allyl,3°>2°>1°1.2RadialOxidationwithOxygenChaininitiationChainpropagationDrawamechanismforthefollowingreaction1.3.RadicaladditionreactionInitiationPropagationH-O428H-Cl432H-Br368C-Br272,H-Cl432,H-C403,pi键682－3682.ElectrophilicadditiontoC,Cmultiple

bonds2.1.CarbocationmechanismDirection:ThemorestablecarbocationformpreferentiallyCaution:Carbocationrearrangement!2.2.NiumreactionmechanismminorcontributingstructureSterospecificity:AntiadditionTheelectronegativitytellyouwhichoneisE+.2.3.Oxymercuration-ReductionAbridgedmercurinium:three-center/two-electronbond3.NucleophilicadditiontoC,Cmultiple

bonds4.ConcertedadditiontoC,CmultiplebondsAsynadditionmechanism4.1.Catalytichydrogenation4.2.Hydroboration-Oxidation4.3.OsO4-OxidationCatalyticamountOsO4(expensiveandhighlytoxic)withperoxide4.4.KMnO4-Oxidation4.5.Diels-AlderreactionOverlapbetweenthehighestoccupiedMOofthediene(HOMO)andthelowestunoccupiedMOofthedienophile(LUMO)isthermallyallowedintheDielsAlderReaction,providedtheorbitalsareofsimilarenergy.Thereactionisfacilitatedbyelectron-withdrawinggroupsonthedienophile,sincethiswilllowertheenergyoftheLUMO.Thereare“inversedemand”DielsAlderReactionsthatinvolvetheoverlapoftheHOMOofthedienophilewiththeLUMOofthediene.Thisalternativescenarioforthereactionisfavoredbyelectron-donatinggroupsonthedienophileandanelectron-poordiene.Theendoproductisusuallyfavoredbykineticcontrolduetosecondaryorbitalinteractions.Thereactionisdiastereoselective.5.SubstitutionReactions5.1NuclephilicSubstitutionReactionsSN1SN2SN1SN2TertiaryalkylPrimaryalkylPoornucleophileGoodnucleophilePolarsolventNonpolarsolventGoodLeavinggroupPoorleavinggroup5.2ElectrophilicAromaticSubstitutionReactions5.3NucleophilicAromaticSubstitutionReactionsR=groupwithboth-Iand-Ceffects6.EliminationreactionsE1E2E1cbSaytzeffruleHofmannruleHofmannruleγ-branchesresultsinHofmannproduct7.NameReactions7.1.Aldolcondensation7.2.Arndt-EistertSynthesis-Wolffrearrangement

7.3.BenzoinCondensationX.Linghu,J.S.Johnson,Angew.Chem.,2003,115,2638KeyIntermediate:7.4.ClaisenCondensationKeyIntermediate:DieckmannCondensation7.5.CannizzaroReaction7.6.Diazotisation7.7.HaloformReaction

7.8.Hell-Volhard-Zelinsky