有机化学课件3The-Nature-of-Organic-Reactions

CHAPTER3TheNatureofOrganicReactions-Alkenes13.1NamingAlkenes1.Name the parent hydrocarbon,find the longest carbon chain that contains the double bond.命名母体烯烃命名母体烯烃 2.Number the carbon atoms in the chain 给主链碳原子编号给主链碳原子编号 3.Write the full name 给出完整的命名给出完整的命名22-hexene2-methyl 3-hexene5-methyl 1,3-cyclohexadienecyclopentene3Vinyl groupPropanyl groupAllyl group Methylene Ethylene Isopropylene4*3.2 cis-trans isomers of Alkenes烯烃的顺烯烃的顺反异构体反异构体RotationofBondIsProhibitive5Thepresenceofacarbon-carbondoublecancreatetwopossiblestructurescisisomer-twosimilargroupsonsamesideofthedoublebondtransisomersimilargroupsonoppositesidesEachcarbonmusthavetwodifferentgroupsforthese(cis/trans)isomerstooccur6Cis-TransIsomersRequireThatEndGroupsMustDifferinPairsBottompaircannotbesuperposed(重叠)by180rotationwithoutbreakingC=CX7891011121314Sequence Rules:The E,Z Designation E,Z 标示的次序规则标示的次序规则 Neithercompoundisclearly“cis”or“trans”SubstituentsonC1aredifferentthanthoseonC2Weneedtodefine“similarity”inaprecisewaytodistinguishthetwostereoisomersCis/transnomenclatureonlyworksfordisubstituteddoublebonds151.Consideringeachofthedouble-bondcarbonsseparately,identifythetwoatomsdirectlyattachedandrankthemaccordingtoatomicnumber分别考虑与双键碳原子直接相连的原子，根据原子序数排序2.Ifadecisioncantbereachedbyrankingthefirstatomsinthesubstituent,lookatthesecond,third,orforthatomsawayfromthedouble-bondcarbonsuntilthefirstdifferenceisfound如果第一个原子难以判别，再看第二、三、四个原子直到能够作出区分3.Multiple-bondedatomsareequivalenttothesamenumberofsingle-bondedatoms多键原子相等于同样数量的单键原子16RankingPriorities:Cahn-Ingold-PrelogRulesMust rank atoms that are connected at comparison point Higher atomic number gets higher priority Br Cl O N C HIn this case,The higher priority groups are opposite:(E)-2-bromo-2-chloro-propene17E,ZStereochemicalNomenclaturePriorityrulesofCahn,Ingold,andPrelogComparewherehigherprioritygroupiswithrespecttobondanddesignateasprefixE-entgegen,oppositesidesZ-zusammen,togetheronthesameside18Ifatomicnumbersarethesame,compareatnextconnectionpointatsamedistanceCompareuntilsomethinghashigheratomicnumberDonotcombinealwayscompareExtendedComparison1920212223*3.3KindsofOrganicReactionsIngeneral,welookatwhatoccursandtrytolearnhowithappensCommonpatternsdescribethechangesAdditionreactionstwomoleculescombineEliminationreactionsonemoleculesplitsintotwoSubstitutionreactionpartsfromtwomoleculesexchangeRearrangementreactionsamoleculeundergoeschangesinthewayitsatomsareconnected2425HowOrganicReactionsOccur:MechanismsInaclockthehandsmovebutthemechanismbehindthefaceiswhatcausesthemovementInanorganicreaction,weseethetransformationthathasoccurred.ThemechanismdescribesthestepsbehindthechangesthatwecanobserveReactionsoccurindefinedstepsthatleadfromreactanttoproduct26nucleophileelectrophile+-27 OrganicReactions:Radical:Polar:28HomogenicFormationofaBondOneelectroncomesfromeachfragmentNoelectronicchargesareinvolvedandNotcommoninorganicchemistry29HeterogenicFormationofaBond OnefragmentsuppliestwoelectronsOnefragmentsuppliesnoelectronsCombinationcaninvolveelectronicchargesandCommoninorganicchemistry30*AnExampleofaPolarReaction:AdditionofHCltoEthylenenucleophileElectrophile313233DescribingaReaction:RatesandEquiilibria 34 Theenergyneededtogofromreactanttotransitionstateistheactivation energy(DG).Thehighestenergypointinareactionstepiscalledthetransition stateDescribingaReaction:ReactionEnergyDiagramsandTransitionStates35DescribingaReaction:IntermediateHBr,aLewisacid,addstothebondThisproducesanintermediatewithapositivechargeoncarbon-acarbocation(碳正离子)Thisisreadytoreactwithbromide36Ifareactionoccursinmorethanonestep,itmustinvolvespeciesthatareneitherthereactantnorthefinalproduct.Theyarecalledreaction intermediatesorsimply“intermediates”.Eachstephasitsownfreeenergyofactivation.Thecompletediagramforthereactionshowsthefreeenergychangesassociatedwithanintermediate37EnergyDiagramforElectrophilicAddition Ratedetermining(slowest)stephashighestenergytransitionstateIndependentofdirectionInthiscaseitisthefirststepinforwarddirection“rate”isnotthesameas“rateconstant”38CarbocationIntermediateReactswithAnionBromideionaddsanelectronpairtothecarbocationAnalkylhalideproducedThecarbocationisareactiveintermediate39ReactionDiagramforAdditionofHBrtoEthylene40MechanisticSourceofRegiospecificityinAdditionReactions Ifadditioninvolvesacarbocationintermediateandtherearetwopossiblewaystoaddtherouteproducingthemorealkylsubstitutedcationiccenterislowerinenergyalkylgroupsstabilizecarbocation413.4AdditionofHXtoAlkenes:HydrohalogenationGeneralreactionmechanism:electrophilic additionAttackofelectrophile(suchasHBr)onbondofalkeneProducescarbocationandbromideionCarbocationisanelectrophile,reactingwithnucleophilicbromideion42TwostepprocessFirsttransitionstateishighenergypointElectrophilicAdditionEnergyPath43ExampleofElectrophilicAdditionAdditionofhydrogenbromideto2-Methyl-propeneH-BrtransfersprotontoC=CFormscarbocationintermediateMorestablecationformsBromideaddstocarbocation44OrientationofElectrophilicAddition:MarkovnikovsRuleInanunsymmetricalalkene,HXreagentscanaddintwodifferentways,butonewaymaybepreferredovertheotherIfoneorientationpredominates,thereactionisregiospecific(位置选择位置选择性性)Markovnikovobservedinthe19thcenturythatintheadditionofHXtoalkene,theHattachestothecarbonwiththemostHsandXattachestotheotherend(totheonewiththemostalkylsubstituents)ThisisMarkovnikovs rule(马氏规则马氏规则)45AdditionofHClto2-methylpropeneRegiospecificoneproductformswheretwoarepossibleExampleofMarkovnikovsRule46EnergyofCarbocationsandMarkovnikovsRuleMorestablecarbocationformsfasterTertiarycationsandassociatedtransitionstatesaremorestablethanprimarycations47CarbocationStructureandStabilityCarbocationsareplanarandthetricoordinatecarbonissurroundedbyonly6electronsinsp2orbitalsThefourthorbitaloncarbonisavacantp-orbitalThestabilityofthecarbocationisincreasedbythepresenceofalkylsubstituentsThereforestabilityofcarbocations:3 2 1 +CH34849503.5AdditionofH2OtoAlkenes:Hydration51523.6 Addition of Water to Alkenes:Oxymercuration(羟汞化反应羟汞化反应)Forlaboratory-scalehydrationofanalkeneUsemercuricacetateinTHFfollowedbysodiumborohydrideMarkovnikovorientationviamercuriniumion533.7AdditionofWatertoAlkenes:Hydroboration(硼氢化反应)Borane(BH3)iselectrondeficientisaLewisacidBoraneaddstoanalkenetogiveanorganoboraneH.C.Brown54AdditionofWatertoAlkenes:Hydroboration(硼氢化反应)Borane(BH3)iselectrondeficientisaLewisacidBoraneaddstoanalkenetogiveanorganoboraneH.C.Brown55BH3isaLewisAcidSixelectronsinoutershellCoordinatestooxygenelectronpairsinethers56 AdditionofH-BH2(fromBH3-THFcomplex)tothreealkenesgivesatrialkylboraneOxidationwithalkalinehydrogenperoxide(H2O2)inwaterproducesthealcoholderivedfromthealkeneHydroboration-Oxidation Forms an Alcohol from an Alkene 57Orientation in Hydration via HydroborationRegiochemistryisopposite to Markovnikov orientation OHisaddedtocarbonwithmostHsHandOHaddwithsyn stereochemistry,tothesamefaceofthealkene(oppositeofantiaddition)58Hydroboration,ElectronicEffectsGiveNon-Markovnikov Morestablecarbocationisalsoconsistentwithstericpreferences59Hydroboration-OxygenInsertionStepH2O2,OH-insertsOHinplaceofBRetains syn orientation60Oxymercuration(羟汞化反应羟汞化反应)61623.8AdditionofX2toAlkenes:HalogenationBromineandchlorineaddtoalkenestogive1,2-dihaldes,anindustriallyimportantprocessF2istooreactiveandI2doesnotaddCl2reactsasCl+Cl-,Br2issimilar63AdditionofBr2toCyclopentene Addition is exclusively trans+64MechanismofBromineAdditionBr+addstoanalkeneproducingacyclicionBromoniumion(溴鎓离子),bromineshareschargewithcarbonGivestransadditionProduct65BromoniumIonMechanismElectrophilicadditionofbrominetogiveacationisfollowedbycyclizationtogiveabromonium ionThisbromoniunionisareactiveelectrophileandbromideionisagoodnucleophile66TheRealityofBromoniumIonsBromoniumwerepostulatedmorethan60yearsagotoexpainthestereochemicalcourseoftheaddition(togivethetrans-dibromidefromacyclicalkeneOlahshowedthatbromoniumionsarestableinliquidSO2withSbF5andcanbestudieddirectly673.9AdditionofH2toAlkenes:HydrogenationAdditionofH-HacrossC=CReductioningeneralisadditionofH2oritsequivalentRequiresPtorPdaspowdersoncarbonandH2HydrogenisfirstadsorbedoncatalystReactionisheterogeneous(processisnotinsolution)68HydrogenAddition-SelectivitySelectiveforC=C.NoreactionwithC=O,C=NPolyunsaturatedliquidoilsbecomesolidsIfonesideisblocked,hydrogenaddstoother69MechanismofCatalyticHydrogenationHeterogeneousreactionbetweenphasesAdditionofH-Hissyn703.10OxidationofAlkenesHydroxylationaddsOHtoeachendofC=CCatalyzedbyKMnO4/OH-StereochemistryofadditionissynProductisa1,2-dialcoholordiol(alsocalledaglycol)71PermanganteOxidationofAlkenesinacidmediumcleavealkenesPotassiumpermanganate(KMnO4)canproducecarboxylicacidsandcarbondioxideifHsarepresentonC=C72Reaction with osmium tetraoxide7374AlkenesCleavage:OzoneOzone,O3,addstoalkenestoformmolozonideReducemolozonidetoobtainketonesand/oraldehydes75ExamplesofOzonolysisofAlkenes Usedindeterminationofstructureofanunknownalkene76StructureElucidationWithOzone Cleavageproductsrevealanalkenesstructure77Epoxidation Reaction783.11 Halohydrin formation(-卤代醇的产生卤代醇的产生)793.12 Addition of carbene(卡宾卡宾):cyclopropane synthesis80Dichlorocarbene:8182Simmons-Smith Reaction833.13 Allylic bromination(烯丙基溴代反应烯丙基溴代反应)8485868788CH2=CHCH2CH3+HBrPeroxideBrCH2CH2CH2CH3*Peroxide effectCH2=CHCH3+Cl25000CCH2=CHCH2Cl893.14AlkenePolymersApolymerisaverylargemoleculeconsistingofrepeatingunitsofsimplermolecules,formedbypolymerizationAlkenesreactwithradicalcatalyststoundergoradicalpolymerizationEthyleneispolymerizedtopolyethylene,forexample 90FreeRadicalPolymerizationofAlkenes AlkenescombinemanytimestogivepolymerReactivityinducedbyformationoffreeradicals91FreeRadicalPolymerization:InitiationInitiation(引发)-afewradicalsaregeneratedbythereactionofamoleculethatreadilyformsradicalsfromanonradicalmoleculeAbondisbrokenhomolytically92Polymerization:PropagationRadicalfromintiationaddstoalkenetogeneratealkenederivedradicalThisradicaladdstoanotheralkene,andsoonmanytimes93Polymerization:TerminationChainpropagationendswhentworadicalchainscombineNotcontrolledspecificallybutaffectedbyreactivityandconcentration94OtherPolymersOtheralkenesgiveothercommonpolymers95UnsymmetricalMonomersIfalkeneisunsymmetrical,reactionisviamorehighlysubstitutedradical 96CationicPolymerizationVinylmonomersreactwithBrnstedorLewisacidtoproduceareactivecarbocationthataddstoalkenesandpropagatesvialengtheningcarbocations973.15PreparationofAlkenes:Eliminationreactionsadditionelimination981.Dehydrohalogenation99100101 Zaizsevs rule:in the elimination of HX from an alkyl halide,the more highly substituted alkene product predominates.1022.Dehydration1033.Dehalogenation1043.16ConjugatedDienesCompoundscanhavemorethanonedoubleortriplebondIftheyareseparatedbyonlyonesinglebondtheyareconjugated(共共轭轭)andtheirorbitalsinteractTheconjugated diene1,3-butadienehaspropertiesthatareverydifferentfromthoseofthenonconjugated diene,1,5-pentadiene105*MeasuringStabilityConjugateddienesaremorestablethannonconjugatedbasedonheatsofhydrogenationHydrogenating1,3-butadienetakesup16kJ/molmoreheatthan1,4-pentadiene106Conjugation effectisaseriesofoverlappingporbitals,usuallyinalternatingsingleandmultiplebonds.-conjugation:Aseriosofoverlappingporbitals,usuallyinalternatingsingleandmultiplebonds.Forexample,1,3-butadieneisaconjugateddiene,3-buten-2-oneisaconjugatedenone,andbenzeneisacyclicconjugatedtriene107p-conjugation:Thedonationorwithdrawalofelectronsthroughorbitaloverlapwithneighboring bonds(a).Hyperconjugation(超共轭):AninteractionthatresultsfromoverlapofavacantporbitalononeatomwithaneithboringCHbond(b).108MolecularOrbitalDescriptionof1,3-ButadieneThesinglebondbetweentheconujgateddoublebondsisshorterandstrongerthansp3Thebonding-orbitalsaremadefrom4porbitalsthatprovidegreaterdelocalizationandlowerenergythaninisolatedC=CThe4molecularorbitalsincludefewertotalnodesthanintheisolatedcaseInaddition,thesinglebondbetweenthetwodoublebondsisstrengthenedbyoverlapofporbitalsInsummary,wesayelectronsin1,3-butadienearedelocalizedoverthebondsystemandDelocalizationleadstostabilization109110CarbocationsfromConjugatedDienesAdditionofH+leadstodelocalizedsecondaryallyliccarbocation111Additiontoaconjugateddieneatorbelowroomtemperaturenormallyleadstoamixtureofproductsinwhichthe1,2adductpredominatesoverthe1,4adductAthighertemperature,productratiochangesand1,4adductpredominates112ProductsofAdditiontoDelocalizedCarbocation NucleophilecanaddtoeithercationicsiteThetransitionstatesforthetwopossibleproductsarenotequalinenergy113*Kineticvs.ThermodynamicControlofReactionsAtcompletion,allreactionsareatequilibriumandtherelativeconcentrationsarecontrolledbythedifferencesinfreeenergiesofreactantsandproducts(ThermodynamicControl)Ifareactionisirreversibleorifareactionisfarfromequilibrium,thentherelativeconcentrationsofproductsdependsonhowfasteachforms,whichiscontrolledbytherelativefreeenergiesofthetransitionstatesleadingtoeach(KineticControl)114115116117*TheDiels-AlderCycloadditionReactionConjugatedienescancombinewithalkenestoformsix-memberedcycliccompoundsTheformationoftheringinvolvesnointermediate(concertedformationoftwobonds)DiscoveredbyO.P.H.DielsandK.AlderinGermanyinthe1930s118Characteristics of the Diels-Alder Reaction Thealkenecomponentiscalledadienophile(亲双烯体亲双烯体)C=Cisconjugatedtoanelectronwithdrawinggroup,suchasC=OorCNAlkynescanalsobedienophiles119120StereospecificityoftheDiels-AlderReactionThereactionisstereospecific,maintainingrelativerelationshipsfromreactanttoproductThereisaone-to-onerelationshipbetweenstereoisomericreactantsandproducts121ConformationsofDienesintheDiels-AlderReactionTherelativepositionsofthetwodoublebondsinthedienearethe“cis”or“trans”twoeachotheraboutthesinglebond(beinginaplanemaximizesoverlap)Theseconformationsarecalleds-cisands-trans(“s”standsfor“singlebond”)Dienesreactinthes-cis conformationintheDiels-Alderreaction122123ConjugateddienescanbepolymerizedTheinitiatorforthereactioncanbearadical,oranacidPolymerization:1,4additionofgrowingchaintoconjugateddienemonomerPolymerization1243.17StabilityofAllylicCarbocations:Resonance125126DrawingandInterpretingResonanceForms(共振式)Anythree-atomgroupingwithamultiplebondhastworesonanceforms127RRules for Resonance Forms:1.Individualresonanceformsareimaginary,notreal.2.Resonanceformsdifferonlyintheplacementoftheirornonbondingelectrons.3.Differentresonanceformsofasubstancedonthavetobeequivalent.4.ResonanceformsmustbevalidLewisstructuresandobeynormalrulesofvalence.5.Theresonancehybridismorestablethananyindividualresonanceform.128129130131132133134135