Alkenes & Alkynes F Bio 120309

8/2/2019 Alkenes & Alkynes F Bio 120309

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CompiledbasedonMcMurrysOrganicChemistry1Alkenes&AlkynesAlkenes&AlkynesAlkenes&AlkynesAlkenes&AlkynesCompiledbasedonMcMurrysOrganicChemistry1Alkenes&AlkynesAlkenes&AlkynesAlkenes&AlkynesAlkenes&Alkynes


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NamingofAlkenes2FindlongestcontinuouscarbonchainforrootNumbercarbonsinchainsothatdoublebondcarbonshavelowestpossiblenumbersRingshavecycloprefixNamingofAlkenes2FindlongestcontinuouscarbonchainforrootNumbercarbonsinchainsothatdoublebondcarbonshavelowestpossiblenumbersRingshavecycloprefix


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ManyAlkenesAreKnownbyCommonNamesEthylene=ethenePropylene=propeneIsobutylene=2-methylpropeneIsoprene=2-methyl-1,3-butadiene3ManyAlkenesAreKnownbyCommonNamesEthylene=ethenePropylene=propeneIsobutylene=2-methylpropeneIsoprene=2-methyl-1,3-butadiene3


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NamingAlkynes4Generalhydrocarbonrulesapplywith-yneasasuffixindicatinganalkyneNumberingofchainwithtriplebondissetsothatthesmallestnumberpossibleforthefirstcarbonofthetriplebondMultipletriplebondsare:diynes,triynes,etcDoubleandtriplebondsare:enynesNumbernearestamultiplebond(eitherdoubleortriple)Ifyouhaveachoice,doublebondlowernumberthantripleNamingAlkynes4Generalhydrocarbonrulesapplywith-yneasasuffixindicatinganalkyneNumberingofchainwithtriplebondissetsothatthesmallestnumberpossibleforthefirstcarbonofthetriplebondMultipletriplebondsare:diynes,triynes,etcDoubleandtriplebondsare:enynesNumbernearestamultiplebond(eitherdoubleortriple)Ifyouhaveachoice,doublebondlowernumberthantriple


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ElectronicStructures5Carbonatomsinadoublebondaresp2-hybridizedThreeequivalentorbitalsat120separationinplaneFourthorbitalisatomicporbitalCarbon-carbontriplebondresultsfromsporbitaloneachCformingasigmabondandunhybridizedpXandpyorbitalsformingpbonds.Theremainingsporbitalsformbondstootheratomsat180toC-Ctriplebond.ThebondisshorterandstrongerthansingleordoubleElectronicStructures5Carbonatomsinadoublebondaresp2-hybridizedThreeequivalentorbitalsat120separationinplaneFourthorbitalisatomicporbitalCarbon-carbontriplebondresultsfromsporbitaloneachCformingasigmabondandunhybridizedpXandpyorbitalsformingpbonds.Theremainingsporbitalsformbondstootheratomsat180toC-Ctriplebond.Thebondisshorterandstrongerthansingleordouble


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RotationofpBondIsProhibitiveThispreventsrotationaboutacarbon-carbondoublebond(unlikeacarbon-carbonsinglebond).Createspossiblealternativestructures6RotationofpBondIsProhibitiveThispreventsrotationaboutacarbon-carbondoublebond(unlikeacarbon-carbonsinglebond).Createspossiblealternativestructures6


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Cis-TransIsomerisminAlkenesThepresenceofacarbon-carbondoublecancreatetwopossiblestructurescisisomer-twosimilargroupsonsamesideofthedoublebondtransisomersimilargroupsonoppositesidesCis,transnomenclatureonlyworksfordisubstituteddoublebonds7Cis-TransIsomerisminAlkenesThepresenceofacarbon-carbondoublecancreatetwopossiblestructurescisisomer-twosimilargroupsonsamesideofthedoublebondtransisomersimilargroupsonoppositesidesCis,transnomenclatureonlyworksfordisubstituteddoublebonds7


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SequenceRules:TheE,ZDesignationNeithercompoundisclearlycisortransE-entgegen,oppositesidesZ-zusammen,togetheronthesameside8SequenceRules:TheE,ZDesignationNeithercompoundisclearlycisortransE-entgegen,oppositesidesZ-zusammen,togetheronthesameside8


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AdditionofHalogenstoAlkenes9Bromineandchlorineaddtoalkenestogive1,2-dihalides,anindustriallyimportantprocessCl2reactsasCl+Cl-Br2issimilarAdditionofHalogenstoAlkenes9Bromineandchlorineaddtoalkenestogive1,2-dihalides,anindustriallyimportantprocessCl2reactsasCl+Cl-Br2issimilar


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MechanismofBromineAddition10Br+addstoanalkeneproducingacyclicionBromoniumion,bromineshareschargewithcarbonGivestransadditionMechanismofBromineAddition10Br+addstoanalkeneproducingacyclicionBromoniumion,bromineshareschargewithcarbonGivestransaddition


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ElectrophilicElectrophilicElectrophilicElectrophilicAdditionofHXtoAlkenesAdditionofHXtoAlkenesAdditionofHXtoAlkenesAdditionofHXoAlkenes11Generalreactionmechanism:electrophilicadditionAttackofelectrophile(suchasHBr)onpbondofalkeneProducescarbocationandbromideionCarbocationisanelectrophile,reactingwithnucleophilicbromideionR-H+A-BR-A+H-BReaksisubstitusiex.Halogenasi>C=CC=C


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ExampleofElectrophilicAdditionAdditionofhydrogenbromideto2-Methyl-propeneH-BrtransfersprotontoC=CFormscarbocationintermediateMorestablecationformsBromideaddstocarbocation12ExampleofElectrophilicAdditionAdditionofhydrogenbromideto2-Methyl-propeneH-BrtransfersprotontoC=CFormscarbocationintermediateMorestablecationformsBromideaddstocarbocation12


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ElectrophilicAdditionEnergyPath13TwostepprocessFirsttransitionstateishighenergypointElectrophilicAdditionEnergyPath13TwostepprocessFirsttransitionstateishighenergypoint


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EnergyDiagramforElectrophilicAdditionRatedetermining(slowest)stephashighestenergytransitionstateIndependentofdirectionInthiscaseitisthefirststepinforwarddirectionrateisnotthesameasrateconstant14EnergyDiagramforElectrophilicAdditionRatedetermining(slowest)stephashighestenergytransitionstateIndependentofdirectionInthiscaseitisthefirststepinforwarddirectionrateisnotthesameasrateconstant14


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OrientationofElectrophilicAddition:MarkovnikovsMarkovnikovsMarkovnikovsMarkovnikovsRuleRuleRuleRule15Inanunsymmetricalalkene,HXreagentscanaddintwodifferentways,butonewaymaybepreferredovertheotherIfoneorientationpredominates,thereactionisregiospecificMarkovnikovobservedinthe19thcenturythatintheadditionofHXtoalkene,theHattachestothecarbonwiththemostHsandXattachestotheotherend(totheonewiththemostalkylsubstituents)ThisisMarkovnikovsruleOrientationofElectrophilicAddition:MarkovnikovsMarkovnikovsMarkovnikovsMarkovnikovsRuleRuleRuleRule15Inanunsymmetricalalkene,HXreagentscanaddintwodifferentways,butonewaymaybepreferredovertheotherIfoneorientationpredominates,thereactionisregiospecificMarkovnikovobservedinthe19thcenturythatintheadditionofHXtoalkene,theHattachestothecarbonwiththemostHsandXattachestotheotherend(totheonewiththemostalkylsubstituents)ThisisMarkovnikovsrule


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ExampleofMarkovnikovsRule16AdditionofHClto2-methylpropeneRegiospecificoneproductformswheretwoarepossibleIfbothendshavesimilarsubstitution,thennotregiospecificExampleofMarkovnikovsRule16AdditionofHClto2-methylpropeneRegiospecificoneproductformswheretwoarepossibleIfbothendshavesimilarsubstitution,thennotregiospecific


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EnergyofEnergyofEnergyofEnergyofCarbocationsCarbocationsCarbocationsCarbocationsandandandandMarkovnikovsMarkovnikovsMarkovnikvsMarkovnikovsRuleRuleRuleRule17MorestablecarbocationformsfasterTertiarycationsandassociatedtransitionstatesaremorestablethanprimarycationsEnergyofEnergyofEnergyofEnergyofCarbocationsCarbocatonsCarbocationsCarbocationsandandandandMarkovnikovsMarkovnikovsMarkovnikovsMarkovnikovsRuleRuleRuleRule17MorestablecarbocationformsfasterTertiarycationsandassociatedtransitionstatesaremorestablethanprimarycations


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MechanisticSourceofRegiospecificityinAdditionReactions18IfadditioninvolvesacarbocationintermediateandtherearetwopossiblewaystoaddtherouteproducingthemorealkylsubstitutedcationiccenterislowerinenergyalkylgroupsstabilizecarbocationMechanisticSourceofRegiospecificityinAdditionReactions18Ifadditioninvolvesacarbocationintermediateandtherearetwopossiblewaystoaddtherouteproducingthemorealkylsubstitutedcationiccenterislowerinenergyalkylgroupsstabilizecarbocation


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CarbocationStructureandStability19Carbocationsareplanarandthetricoordinatecarbonissurroundedbyonly6electronsinsp2orbitalsThefourthorbitaloncarbonisavacantp-orbitalThestabilityofthecarbocation(measuredbyenergyneededtoformitfromR-X)isincreasedbythepresenceofalkylsubstituentsThereforestabilityofcarbocations:3>2>1>+CH3CarbocationStructureandStability19Carbocationsareplanarandthetricoordinatecarbonissurroundedbyonly6electronsinsp2orbitalsThefourthorbitaloncarbonisavacantp-orbitalThestabilityofthecarbocation(measuredbyenergyneededtoformitfromR-X)isincreasedbythepresenceofalkylsubstituentsThereforestabilityofcarbocations:3>2>1>+CH3


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7.4AdditionofWaterto7.4AdditionofWaterto7.4AdditionofWaterto7.4AdditionofWatertoAlkenes(Hydration)Alkenes(Hydration)Alkenes(Hydration)Alkenes(Hydration)20HydrationofanalkeneistheadditionofH-OHtotogiveanalcoholAcidcatalystsareusedinhightemperatureindustrialprocesses:ethyleneisconvertedtoethanol7.4AdditionofWaterto7.4AdditionofWaterto7.4AdditionofWaterto7.4AdditionofWatertoAlkenes(Hydration)Alkenes(Hydration)Alkenes(Hydration)Alkenes(Hydration)20HydrationofanalkeneistheadditionofH-OHtotogiveanalcoholAcidcatalystsareusedinhightemperatureindustrialprocesses:ethyleneisconvertedtoethanol


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7.5AdditionofWatertoAlkenes:Hydroboration21HerbertBrown(HB)inventedhydroboration(HB)Borane(BH3)iselectrondeficientisaLewisacidBoraneaddstoanalkenetogiveanorganoborane7.5AdditionofWatertoAlkenes:Hydroboration21HerbertBrown(HB)inventedhydroboration(HB)Borane(BH3)iselectrondeficientisaLewisacidBoraneaddstoanalkenetogiveanorganoborane


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22AdditionofH-BH2(fromBH3-THFcomplex)tothreealkenesgivesatrialkylboraneOxidationwithalkalinehydrogenperoxideinwaterproducesthealcoholderivedfromthealkeneHydroboration-OxidationFormsanAlcoholfromanAlkene22AdditionofH-BH2(fromBH3-THFcomplex)tothreealkenesgivesatrialkylboraneOxidationwithalkalinehydrogenperoxideinwaterproducesthealcoholderivedfromthealkeneHydroboration-OxidationFormsanAlcoholfromanAlkene


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BH3IsaLewisAcid23SixelectronsinoutershellCoordinatestooxygenelectronpairsinethersBH3IsaLewisAcid23SixelectronsinoutershellCoordinatestooxygenelectronpairsinethers


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OrientationinHydrationviaHydroboration24RegiochemistryisoppositetoMarkovnikovorientationOHisaddedtocarbonwithmostHsHandOHaddwithsynstereochemistry,tothesamefaceofthealkene(oppositeofantiaddition)OrientationinHydrationviaHydroboration24RegiochemistryisoppositetoMarkovnikovorientationOHisaddedtocarbonwithmostHsHandOHaddwithsynstereochemistry,tothesamefaceofthealkene(oppositeofantiaddition)


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MechanismofHydroborationBoraneisaLewisacidAlkeneisLewisbaseTransitionstateinvolvesanionicdevelopmentonBThecomponentsofBH3areacrossC=C25MechanismofHydroborationBoraneisaLewisacidAlkeneisLewisbaseTransitionstateinvolvesanionicdevelopmentonBThecomponentsofBH3areacrossC=C25


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Hydroboration:OrientationinAdditionStep26Additioninleastcrowdedorientation,synAdditionalsoisviamoststablecarbocationHydroboration:OrientationinAdditionStep26Additioninleastcrowdedorientation,synAdditionalsoisviamoststablecarbocation


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Hydroboration,ElectronicEffectsGiveNon-Markovnikov27MorestablecarbocationisalsoconsistentwithstericpreferencesHydroboration,ElectronicEffectsGiveNon-Markovnikov27Morestablecarbocationisalsoconsistentwithstericpreferences


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Hydroboration-OxygenInsertionStep28H2O2,OH-insertsOHinplaceofBRetainssynorientationHydroboration-OxygenInsertionStep28H2O2,OH-insertsOHinplaceofBRetainssynorientation


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ReductionReductionReductionReductionofAlkenesofAlkenesofAlkenesofAlkenes:Hydrogenation29AdditionofH-HacrossC=CReductioningeneralisadditionofH2oritsequivalentRequiresPtorPdaspowdersoncarbonandH2HydrogenisfirstadsorbedoncatalystReactionisheterogeneous(processisnotinsolution)ReductionReductionReductionReductionofAlkenesofAlkenesofAlkenesofAlkenes:Hydrogenation29AdditionofH-HacrossC=CReductioningeneralisadditionofH2oritsequivalentRequiresPtorPdaspowdersoncarbonandH2HydrogenisfirstadsorbedoncatalystReactionisheterogeneous(processisnotinsolution)


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HydrogenAddition-Selectivity30SelectiveforC=C.NoreactionwithC=O,C=NPolyunsaturatedliquidoilsbecomesolidsIfonesideisblocked,hydrogenaddstootherHydrogenAddition-Selectivity30SelectiveforC=C.NoreactionwithC=O,C=NPolyunsaturatedliquidoilsbecomesolidsIfonesideisblocked,hydrogenaddstoother


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MechanismofCatalyticHydrogenation31HeterogeneousreactionbetweenphasesAdditionofH-HissynMechanismofCatalyticHydrogenation31HeterogeneousreactionbetweenphasesAdditionofH-Hissyn


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AlkeneCleavage:Ozone32Ozone,O3,addstoalkenestoformmolozonideReducemolozonidetoobtainketonesand/oraldehydesAlkeneCleavage:Ozone32Ozone,O3,addstoalkenestoformmolozonideReducemolozonidetoobtainketonesand/oraldehydes


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ExamplesofOzonolysisofAlkenes33UsedindeterminationofstructureofanunknownalkeneExamplesofOzonolysisofAlkenes33Usedindeterminationofstructureofanunknownalkene


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34AdditionofBromineandChlorineInitialadditionusuallygivestransintermediateCanoftenbestoppedatthisstageifdesired(1eq.Br2)Productwithexcessreagentistetrahalide34AdditionofBromineandChlorineInitialadditionusuallygivestransintermediateCanoftenbestoppedatthisstageifdesired(1eq.Br2)Productwithexcessreagentistetrahalide


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35AdditionofHXtoAlkynesInvolvesVinylicCarbocationsAdditionofH-XtoalkyneshouldproduceavinyliccarbocationintermediateSecondaryvinylcarbocationsareaboutasstableasprimaryalkylcarbocationsPrimaryvinylcarbocationsprobablydonotformatallNonethelss,H-BrcanaddtoanalkynetogiveavinylbromideiftheBrisnotonaprimarycarbon35AdditionofHXtoAlkynesInvolvesVinylicCarbocationsAdditionofH-XtoalkyneshouldproduceavinyliccarbocationintermediateSecondaryvinylcarbocationsareaboutasstableasprimaryalkylcarbocationsPrimaryvinylcarbocationsprobablydonotformatallNonethelss,H-BrcanaddtoanalkynetogiveavinylbromideiftheBrisnotonaprimarycarbon


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36HydrationofAlkynesAdditionofH-OHasinalkenesMercury(II)catalyzesMarkovnikovorientedadditionHydroboration-oxidationgivesthenon-MarkovnikovproductKeto-enolTautomerismTautomerism=IsomericcompoundsthatrapidilyinterconvertbythemovementofaprotonandarecalledtautomersEnolsrearrangetotheisomericketonebytherapidtransferofaprotonfromthehydroxyltothealkenecarbonTheketoformisusuallysostablecomparedtotheenolthatonlytheketoformcanbeobserved36HydrationofAlkynesAdditionofH-OHasinalkenesMercury(II)catalyzesMarkovnikovorientedadditionHydroboration-oxidationgivesthenon-MarkovnikovproductKeto-enolTautomerismTautomerism=IsomericcompoundsthatrapidilyinterconvertbythemovementofaprotonandarecalledtautomersEnolsrearrangetotheisomericketonebytherapidtransferofaprotonfromthehydroxyltothealkenecarbonTheketoformisusuallysostablecomparedtotheenolthatonlytheketoformcanbeobserved


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37Hydroboration/OxidationofAlkynesBH3(borane)addstoalkynestogiveavinylicboraneAnti-MarkovnikovOxidationwithH2O2producesanenolthatconvertstotheketoneoraldehydeProcessconvertsalkynetoketoneoraldehydewithorientationoppositetomercuricioncatalyzedhydration37Hydroboration/OxidationofAlkynesBH3(borane)addstoalkynestogiveavinylicboraneAnti-MarkovnikovOxidationwithH2O2producesanenolthatconvertstotheketoneoraldehydeProcessconvertsalkynetoketoneoraldehydewithorientationoppositetomercuricioncatalyzedhydration


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38ReductionofAlkynesAdditionofH2overametalcatalyst(suchaspalladiumoncarbon,Pd/C)convertsalkynestoalkanes(completereduction)TheadditionofthefirstequivalentofH2producesanalkene,whichismorereactivethanthealkynesothealkeneisnotobserved38ReductionofAlkynesAdditionofH2overametalcatalyst(suchaspalladiumoncarbon,Pd/C)convertsalkynestoalkanes(completereduction)TheadditionofthefirstequivalentofH2producesanalkene,whichismorereactivethanthealkynesothealkeneisnotobserved


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Alkenes & Alkynes F Bio 120309