Acetylene and Other Interesting Alkynes乙炔和其它有趣的炔烴

1Chapter11Alkynes2AlkynesgeneralmolecularformulaCnH2n-2thetriplebondintroducestwodegreesofunsaturation.Introduction—StructureandBonding3Introduction—StructureandBondingCf.pbondinCH2CH2:64Kcal/molBothbondsofaC-CtriplebondareweakerthantheC-Cdoublebondforhomolyticcleavage.Alkynesaremorepolarizablethanalkenes.Cyclooctyneisthesmallestisolablecycloalkyne,thoughitdecomposesuponstandingatroomtemperatureafterashorttime.4AlkynesAlkynesarenamedinthesamegeneralwaythatalkenesarenamed.IntheIUPACsystem,changethe–aneendingoftheparentalkanenametothesuffix–yne.Choosethelongestcontinuouschainthatcontainsbothatomsofthetriplebondandnumberthechaintogivethetriplebondthelowernumber.Compoundswithtwotriplebondsarenamedasdiynes,thosewiththreearenamedastriynesandsoforth.Compoundsbothadoubleandtriplebondarenamedasenynes.Thechainisnumberedtogivethefirstsiteofunsaturation(eitherC=CorCC)thelowernumber.Thesimplestalkyne,H-CC-H,namedintheIUPACsystemasethyne,ismoreoftencalledacetylene,itscommonname.Thetwo-carbonalkylgroupderivedfromacetyleneiscalledanethynylgroup.Nomenclature5AlkynesNomenclature6AlkynesThephysicalpropertiesofalkynesresemblethoseofhydrocarbonsofsimilarshapeandmolecularweight.Alkyneshavelowmeltingpointsandboilingpoints.Meltingpointandboilingpointincreaseasthenumberofcarbonsincreases.Alkynesaresolubleinorganicsolventsandinsolubleinwater.PhysicalProperties7AlkynesAcetyleneandOtherInterestingAlkynesAcetylene(H-CC-H)isacolorlessgasthatburnsinoxygentoformCO2andH2O.Closesthydrocarbontocharcoalandisanexcellentfuel.8AcetyleneandOtherInterestingAlkynes9AlkynesAcetyleneandOtherInterestingAlkynesEthynylestradiolandnorethindronearetwocomponentsoforalcontraceptivesthatcontainacarbon-carbontriplebond.Bothmoleculesaresyntheticanaloguesofthenaturallyoccurringfemalesexhormonesestradiolandprogesterone,butaremorepotentsotheycanbeadministeredinlowerdoses.Mostoralcontraceptivescontainbothofthesesynthetichormones.Theyactbyartificiallyelevatinghormonelevelsinawoman,therebypreventingpregnancy.10AlkynesAcetyleneandOtherInterestingAlkynes11AlkynesAcetyleneandOtherInterestingAlkynesblockstheeffectsofprogesterone,thuspreventingpregnancyandinducingabortionsinterfereswithovulation,andsoitpreventspregnancy12AlkynesAlkynesfromNature13AlkynesPreparationofAlkynes14AlkynesPreparationofAlkynes15IntroductiontoAlkyneReactions—Additions16IntroductiontoAlkyneReactions—Acids&Nucleophile17Hydrohalogenation—ElectrophilicAdditionofHXhydrohalogenation18AlkynesHydrohalogenation—ElectrophilicAdditionofHX19AlkynesElectrophilicadditionofHXtoalkynesisslowerthanelectrophilicadditionofHXtoalkenesIntroductiontoAlkyneReactionsMarkovnikovaddition20AlkynesCarbocationAisstabilizedbyresonance,butBisnot.IntroductiontoAlkyneReactions21AlkynesHalogenation—AdditionofHalogen22AlkynesHalogenation—AdditionofHalogen23AlkynesInthepresenceofstrongacidorHg2+catalyst,theelementsofH2Oaddtothetriplebond.Hydration—ElectrophilicAdditionofWater24AlkynesHydration—ElectrophilicAdditionofWaterInternalalkynesundergohydrationwithconcentratedacidterminalalkynesrequirethepresenceofanadditionalHg2+catalyst—usuallyHgSO4—toyieldmethylketonesbyMarkovnikovadditionofwater.25Tautomerism:theconversionofageneralenolAtothecarbonylcompoundB.AandBaretautomers:AistheenolformandBistheketoformofthetautomer.Hydration—ElectrophilicAdditionofWaterEquilibriumfavorstheketoformlargelybecausetheC=OismuchstrongerthanaC=C.Tautomerization(theprocessofconvertingonetautomerintoanother),iscatalyzedbybothacidandbase.26AlkynesHydration—ElectrophilicAdditionofWater27AlkynesHydration—ElectrophilicAdditionofWater28AlkynesHydroboration—OxidationHydroboration—oxidationisatwostepreactionsequencethatconvertsanalkynetoacarbonylcompound.29AlkynesHydroboration—Oxidation30AlkynesIntroductiontoAlkyneReactions—Acetylideanions31AlkynesReactionsofAcetylideAnionsAcetylidesarestrongnucleophilesthemechanismofsubstitutionisSN2,andthusthereactionisfastestwithCH3Xand10alkylhalides.32AlkynesReactionsofAcetylideAnionsnucleophilicsubstitutionwithacetylideanionsformsnewcarbon-carbonbondsinhighyieldonlywithunhinderedCH3Xand1°alkylhalides.33AlkynesReactionsofAcetylideAnions34AlkynesReactionsofAcetylideAnions35AlkynesReactionsofAcetylideAnionsCarbon—carbonbondformationwithacetylideanionsisavaluablereactionusedinthesynthesisofnumerousnaturalproducts.36AlkynesReactionsofAcetylideAnionsAcetylideanionsaregoodnucleophilesthatopenepoxideringsbyanSN2mechanism.Backsideattackoccursatthelesssubstitutedendoftheepoxide.37AlkynesSynthesisYoucannowbegintoconsider(forexample)howtoprepareafive-carbonproductfromthreesmallerprecursormoleculesusingthereactionsyouhavelearned.Toplanasynthesisofmorethanonestep,weusetheprocessofretrosyntheticanalysis:workingbackwa