天津大学有机化学双语PPT有机化学部分Chapter 5

Chapter5DienesandConjugatedSystems,5.1ClassandNomenclatureofDienes5.2StructureofConjugatedDienesMolecularobitals5.3AllylicCarbocationsHyperconjugation-pHyperconjugation-Hyperconjugation5.4ReactionofconjugatedDienes5.4.1ElectrophilicAttackonConjugatedDienes:1,4-additionMechanismofconjugateaddition,Kineticversusthermodynamiccontrolofreactions5.5TheDiels-AldeCycloadditionReaction,5.1ClassesandNomenclatureofDienes,Analkadiene(二烯烃):,Hydrocarboncontainingtwocarbon-carbondoublebonds,Alkadienes,Isolateddienes,1,4-pentadiene,1,5-Cyclo-octadiene,Separatedbyoneormoresp3-Catom.,Conjugateddienes:,1,3-butadiene,1,3-cyclo-hexadiene,Doublebondsandsinglebondsalternatealongthechain.,Cumulateddienes,Allene(丙二烯),TheCatomiscommonfortwodoublebonds,Nomenclature:,cis,cis2,4-hexadiene,(2Z,4Z)-2,4-hexadiene顺,顺-2,4-己二烯(Z,Z)-2,4-己二烯,(2Z,4E)-2,4-hexadiene,顺,反-2,4-己二烯(Z,E)-,cis,trans-,P127.4.10,5.2StructureofConjugatedDienes,1,3-Butadiene:,4Catomsaresp2-hybridized.,C2-C3bond:sp2-sp2overlap,bond：2p-2poverlap,C2-C3partiallyoverlapby2p-2porbital,4electronsaredelocalizedover4Catoms,Delocalizationofelectronslowerstheenergy.,4Catomsarecoplanar,P128,Twopossibleplanarconformationof1,3-butadiene:,s-Cisconformation,s-Transconformation,Antibondingmolecularorbitals(反键轨道),Thefourporbitalscombinetoformasetofmolecularobitals:,Twoofthemolecularorbitals1,3-butadienearebondingmolecularorbitals.,Bondingmolecularorbitals(成键轨道),Ch.P94.,Molecularorbitalsof1,3-butadiene,node,2-HOMO(Thehighestoccupiedorbital),3*-LUMO(thelowestunoccupiedorbital),-Conjugatesystem:,Thealternatesystembysinglebondanddoublebond.,Characterofconjugatesystem:,electronsdelocalization.,5.3AllylicCarbocations,RelativeOrderofcarbocationstability:,P129,4.11,Allylcation(烯丙基正离子),Allyliccation(烯丙基型正离子),Catomwithpositivechargeissp2-hybridized.porbitalisvacant.,p-overlap.,electronsdelocalization,p-conjugation,Resonancehybrid,Hyperconjugation(超共轭效应),Ch.P96,-pHyperconjugation:,Vacantporbital,sp2hybride,Theorderofstabilityofcarbocations:,C-Hbondattachedapositivecarbondelocalizethepositivecharge,-Hyperconjugation,C-HbondatttachedaCarbon-carbondoublebond,Delocalizationofelectrons,Thestabilityofalkeneisincreasedbyenhanceofdensityofelectroniccloud,5.4ReactionofconjugatedDienes,5.4.1ElectrophilicAttackonConjugatedDienes:1,4-addition,1,3-butadiene,1-Bromo-2-butane(19%),Mechanismoftheaddition:,3-Bromo-1-butane(81%),Step1.,1,2-addition,1,4-addition,Theformationofallyliccarbocation(烯丙基型正离子的生成),Secondaryallyliccation,(I),PrimaryAllyliccation(II),Step2.Cation-anioncombination,Stabilityofallyliccations:(I)(II),1,4-addition,1,2-addition,Kineticversusthermodynamiccontrolofreactions:,Energy,1,2-Additionproduct:,Ratecontrolorkineticcontrolproduct,1,4-Additionproduct:,Equilibriumcontrolorthermodynamiccontrolproduct,5.5TheDiels-AlderCycloadditionReaction,Theconjugateadditionofanalkenetodiene,OttoDielsandKurtAlder(Germany)receivethe1950NobelPrizeinchemistry,DieneDienophileAdduct(双烯体)(亲双烯体)(加成物),Pericyclicreaction(周环反应),MaleicanhydrideisusedtoidentifyconjugateDienes.,CharacteristicoftheDiels-AlderReaction:,1.Thereactionisreversible.,2.Dienophile:withelectron-withdrawinggroup,3.Diene:withelectron-releasinggroupsands-cisconformation,not,4.Stereospecific:Syn-addition,5.Application:,a.Identificationtoconjugatedienes.,b.CyclizationbytheformationofC-Cbond.,ProblemstoChapter5,P1464.374.464.47,Additionalproblems:1.ElectrophilicadditionofBr2toisoprene(异戊二烯)yieldsthefollowingproductmixture:,(3%)(21%),76%),Ofthe1,2-additionproducts,explainwhy3,4-dibromo-3-methyl-1-butene(21%)predominatesover3,4-dibromo-1-butene(3%).,2.Drawthepossibleproductsresultingfromadditionof1equivalentofHClto1-p