有机化学第三章烯烃炔

Chapter3AlkenesandAlkynesTeachingObjectivesandRequirementsUnderstand:UnsaturatedHydrocarbons,Hydrogenation.Grasp:GeometricIsomers,E,ZDesignation,Nomenclature,Oxidation,ElectrophilicAdditionofHydrogenHalides,SulfuricAcid,Halogens,Markovnikov’sRule.Moderatelygrasp:MechanismofAdditiontoAlkenes.KeypointsandAreasofDifficultyElectrophilicAddition,Markovnikov’sRule,Oxidation.3.1UnsaturatedhydrocarbonsCarbon-carbonmultiplebondsFewerhydrogenatomsthanalkaneorcycloalkane—unsaturatedAlkenes—acarbon-carbondoublebondAlkynes—acarbon-carbontriplebondAlkadienes—conjugateddienes3.1UnsaturatedhydrocarbonsTwodoublebondunitsarejoinedbyonesinglebondAlkenesSimplestalkene,monlycalledethylene,IUPACnameetheneSuffix–ene3.1UnsaturatedhydrocarbonsSixatomsofethenearelocatedinthesameplaneGeneralformulaCnH2nAlkynesSimplestalkyne,monlycalledacetylene,IUPACnameethyne3.1UnsaturatedhydrocarbonsSuffix–yneFouratomsofacetylenearelocatedinastraightlineGeneralformulaCnH2n-2

3.2GeometricIsomerismNofreerotationofdoublebondDifferentgroupsbondtothedoublebondcarbonDifferentspatialorgeometricarrangementsGeometricisomersorcis-transisomersTwodifferentgroupsforeachdouble-bondedcarbonatom3.2GeometrismIsomerismTwosamegroupsbondtotwocarbonsofdoublebondThesetwosamegroupsonthesameside—cis,onthetwoside—trans

3.2GeometrismIsomerismOneoftheunsaturatedcarbonatomsisattachedtotwoidenticalgroups—nocis-transisomerismGeometrismisomers,differentphysicalproperties3.3TheE,ZDesignationofGeometricIsomersTri-andtetrasubstitutedalkenes-E,ZsystemofnomenclatureSequencerulestoassignprioritiestothegroups,loworhighHigherprioritygroups—sameside:Zisomer3.3TheE,ZDesignationofGeometricIsomersHigherprioritygroups—oppsiteside:EisomerThesameforlowergroups

SequencerulesHighatomic-numberatom—highpriorityBr>Cl>F>O>N>C>H3.3TheE,ZDesignationofGeometricIsomersComparefromfirstatombondeddirectlytocarbonsofdoublebond,thensecond,…tert-butyl>isopropyl>ethyl>methylDoublebond=twosinglebond,sofortriplebond3.4NomenclatureofAlkenesandAlkynesSubstituentscommonnamesIUPACnamesofalkenesParent:longestcontinuouschain,containdoublebondStemnamesimilartoalkane,enereplaceane3.4NomenclatureofAlkenesandAlkynesSmallestnumberforcarbonofdoublebondEorZinparentheses,infrontofthenamePositionnumber,nameofsubstituents

3.4NomenclatureofAlkenesandAlkynesPositionnumberofdoublebond,thenparentnameDi,triinfrontof–ene,showmorethanonedoublebondCycloalkene,double-bondedcarbonatoms(1or2),smallestnumberofsubstituent3.4NomenclatureofAlkenesandAlkynesIUPACnamesofalkynesynereplaceene,similartoalkenes3.4NomenclatureofAlkenesandAlkynesMultipletriplebonds:diyne,triyneandsoonCompoundswithbothdoubleandtriplebondsareenynes,notynenesStartnumberingfromtheendnearestthefirstmultiplebondDoublebondsareassignedlowernumbers3.5HygenationofAlkenesandAlkynesReductionofalkenesReactwithhydrogengasDoublebondchangestosinglebondCatalyst:nickelorplatinumC-Odoublebondwon’tbereduced3.5HygenationofAlkenesandAlkynesSamefaceadditionoftwohydrogenatomsReductionofalkynes

Similartoalkenes3.5HygenationofAlkenesandAlkynesTwomolarequivalentsofhydrogengas—saturatedcompoundsAlkeneproductbyLindlarcatalyst—cisaddition3.5HygenationofAlkenesandAlkynesReductionwithlithiummetalinliquidammonia—transaddition3.6OxidationofAlkenesandAlkynesHydroxylationofalkenesPotassiumpermanganate(KMnO4)Mildcondition:basic,lowtemperatureProductoftwoneighborhydroxylgroupsOncarbonsoftheoriginaldouble-bondunit3.6OxidationofAlkenesandAlkynesPotassiumpermanganate:purplesolutionManganesedioxide:abrownsolidPhenomenon:purplechangetobrownTestthepresenceofdoublebondbycolorOzonolysisofalkenesandalkynesOzone,O3,reactintwosteps3.6OxidationofAlkenesandAlkynesProductforalkenes:carbonylcompoundsWithoutconcernthestructure,justkeepitChangetheoneCofcarbon-carbondoublebondwithOProductforalkynes:carboxylicacidsSimilartoalkenes:twoOreplaceoneC3.7AdditionReactionsofAlkenesandAlkynesSymmetricalreagentsconsistoftwoidenticalgroups,Br2Unsymmetricalreagentsconsistoftwodifferentgroups,HClandH2OAdditionofhalogensReddishbrominegivecolorlessproductDeterminetheunsaturatedcompounds3.7AdditionReactionsofAlkenesandAlkynes

ChlorinealsoaddstodoublebondsIodine:badyield3.7AdditionReactionsofAlkenesandAlkynesFluorine:tooreactivetocontrol

AdditionofhydrogenhalidesHXisunsymmetricreagentForsymmetricalkenesHandXaddtoanycarbonofdoublebond3.7AdditionReactionsofAlkenesandAlkynesForunsymmetricalkenes,twochoices

Markovnikov’sRuleHaddstocarbonwithmoreHatoms3.8MechanismofAdditionReactionsπelectrons-anucleophile(nucleuslover)Acceptanelectrophile(electron-lovingspecies)HBrmaybeconsideredasH+andBr–

H+,anelectrophile,reactsfirstwithπbondApositivelychargedspecies-carbocation

3.8MechanismofAdditionReactionsPositivelychargedC+

attachestonegativelychargedBr–

Forpropene,H+hastwopossibleattachmenttocarbonatoms3.8MechanismofAdditionReactions3.8MechanismofAdditionReactions3.8MechanismofAdditionReactionsFormpropylorisopropylcarbocationsMorestable:isopropylcarbocationMorestablecarbocationformsproductSo2-bromopropanenot1-bromopropaneAlkylcangiveelectronstopositivechargeMoresubstitutedcarbocationmorestable3.9HydrationofAlkenesandAlkynesH2OfitsthegeneralclassofHX(H—OH)InaccordancewithMarkonikov’sruleHydrationofalkynesproducescarbonylcompoundsInthepresenceofmercuricsulfatecatalystEnol=en+ol,alkene+alcohol3.9HydrationofAlkenesandAlkynesEnolconverttomorestablecarbonyl3.10PreparationofAlkenesandAlkynesDehydrationofalcoholsRequiresstrongconcentratedacidssulfuricacid,H2SO4,orphosphoricacid,H3PO4

ElimiantionreactionBreakingthecarbon-oxygenbond3.10PreparationofAlkenesandAlkynesBreakingcarbon-hydrogenbondonanadjacentcarbonatomFor2-butanol,twodifferentcarbonatomsareadjacenttotheOH-bearingcarbonatomEachcouldreleaseahydrogenatom

3.10PreparationofAlkenesandAlkynesProduceamixtureofproductsThegreaternumberofalkylgroupsattachedtothedoublebondpredominatesMainproduct:themoresubstitutedalkeneZaitsev’srule:givethemoresubstituteddoublebond3.10PreparationofAlkenesandAlkynes3-pentanol,yieldcis-andtrans-2-penteneThetransisomeristhemajorproduct,alsothemorestableisomerInthetransisomerthealkylgroupsarewellseparatedInthecisisomerthealkylgroupsarenear3.10PreparationofAlkenesandAlkynesTheproximityofthealkylgroupscausesterichindranceThegroupsrepeleachotherTransisomerismorestable,predominates

DehydrohalogenationEliminationoftheelementsHandXasinHClorHBrfromadjacentcarbonatoms3.10PreparationofAlkenesandAlkynesProductisalkeneRequireabase,representedbyB-

UsuasllyalkoxideionsuchasC2H5O-

MorehighlysubstitutedalkenepredominateTransisomersarefavoredovercisisomers3.10PreparationofAlkenesandAlkynesEliminationreactionsofdihalidesThereactantisavicinaldihalideTwomolarequivalentsofHXmustbeeliminated3.10PreparationofAlkenesandAlkynesPro