文稿介绍说明

OrganicChemistryOrganicChemistry(Chapter13Nuclearmagneticresonancespectroscopyandmassspectroscopy)JoelleWang(汪君)1OrganicChemistry:InfraredOrganicChemistry:Infrared(IR)Spectroscopy（红外光谱ToreceiveinformationaboutfunctionalUltraviolet(UV)Spectroscopy（紫外光谱Toreceiveinformationabout-conjugatedMassSpectroscopy(MS)（质谱ToreceiveinformationaboutthemolecularweightofunknownmoleculeinNuclearMagneticResonance(NMR)Spectroscopy（核磁共Toreceiveinformationofthehydrogenatomscarbon2P428ProblemP428Problem12-344ChapterChapter13NuclearmagneticresonancespectroscopyandmassspectroscopyNuclearmagneticresonanceH-1NMRCarbon-13NMRMassDeterminationofthemolecular5NuclearmagneticNuclearmagneticNuclearmagneticresonancespectroscopy(NMR)isthemostpowerfulavailablefororganicstructureNMRisusedtostudyawidevarietyofnuclei,including1H,13C,15N,19F,and31P.Organicchemistsfindproton(1H)andcarbon-13(13C)NMRtobemostusefulbecausehydrogenandcarbonaremajorcomponentsoforganiccompounds.AnucleuswithanoddatomicnumberoranoddmassnumberhasanuclearspinthatcanbeobservedbytheNMRspectrometer.原子数是奇数或质量数是奇数具有可以被NMR观测到的核自旋。Aprotonisthesimplestnucleus,anditsoddatomicnumberof1impliesithasaspin.Itgeneratesamagneticfield(symbolizedbyB),calledthemagneticmoment,thatlookslikethefieldofasmallbarmagnet.6NuclearmagneticWhenaNuclearmagneticWhenasmallbarmagnetisplacedinthefieldofalargermagnet,ittwiststoalignitselfwiththefieldofthelargermagnet-alowerenergyarrangementthananorientationagainstthefield.7NuclearmagneticNuclearmagneticThesameeffectisseenwhenaprotonisplacedinanexternalmagneticfield(Bo).Quantummechanicsrequirestheproton'smagneticmomenttobealignedeitherwiththeexternalfieldoragainstthefield.Thelower-energystatewiththeprotonalignedwiththefieldiscalledthealpha-spin(α-spin)state.Thehigher-energystatewiththeprotonalignedagainsttheexternalmagneticfieldiscalledthebeta-spin(β-spin)state.质子的磁矩与磁场方向一致时，能量最低，称为α-的方向相反时，能量最高，称为βIntheabsenceofanexternalmagneticfield,protonmagneticmomentshaverandomorientations.Whenanexternalmagneticfieldisapplied,therearemoreα-spinsthanβ-spins.8NuclearmagneticInastrongmagneticfield,theenergydifferencebetweenthetwospinstatesislargerthanitisinaweakerfield.Infact,theenergydifferenceisNuclearmagneticInastrongmagneticfield,theenergydifferencebetweenthetwospinstatesislargerthanitisinaweakerfield.Infact,theenergydifferenceisproportionaltothestrengthofthemagneticfield.ΔE=energydifferencebetweenαandα、β-h=Planck‘sBo=strengthoftheexternalmagneticγ=gyromagneticratio,26,753sec-1gauss-1foraprotonWhenanucleusissubjectedtotherightcombinationofmagneticfieldandelectromagneticradiationtoflipitsspin,itissaidtobe"inresonance",anditsabsorptionofenergyisdetectedbytheNMRspectrometer.Thisistheoriginoftheterm"nuclearmagneticresonance".9NuclearmagneticNuclearmagneticMagneticShieldingbyElectronsInamolecule,theelectroncloudaroundeachnucleuscirculateandgenerateainducedmagneticfieldthatopposestheexternallyappliedTheresultisthatthemagneticfieldatthenucleusisweakerthantheexternalfield,andwesaythenucleusisshielded.Theeffectivemagneticfieldattheshieldedprotonisalwaysweakerthantheexternalfield,sotheappliedfieldmustbeincreasedforresonancetooccuratagivenfrequency.Ifallprotonswereshieldedbythesameamount,theywouldallbeinresonanceatthesamecombinationoffrequencyandmagneticfield.Fortunately,protonsindifferentchemicalenvironmentsareshieldedbydifferentamounts.NuclearmagneticNuclearmagneticMagneticShieldingbyElectronsBecauseofthediverseandcomplexstructuresoforganicmolecules,theshieldingeffectsofelectronsatvariouspositionsaregenerallydifferent.Acarefulmeasurementofthefieldstrengthsrequiredforresonanceofthevariousprotonsinamoleculeprovidesuswithtwoimportanttypesofinformation:Thenumberofdifferentabsorptions(alsocalledsignalsorpeaks)implieshowmanydifferenttypesofprotonsarepresent.Theamountofshieldingshownbytheseabsorptionsimpliestheelectronicstructureofthemoleculeclosetoeachtypeofproton.NuclearmagneticNuclearmagneticMagneticShieldingbyElectronsTwootheraspectsoftheNMRspectrumwewillconsideraretheintensitiesofthesignalsandtheirsplittingpatterns:TheintensitiesofthesignalsimplyhowmanyprotonsofeachtypeareThesplittingofthesignalsgivesinformationaboutothernearbyNuclearmagneticNuclearmagneticTheNMRSpectrometer核磁共振仪ThesimplesttypeofNMRspectrometerconsistsoffourAstablemagnet,withasensitivecontrollertoproduceaprecisemagneticfield.Aradio-frequency(RF)transmitter,emittingapreciseAdetectortomeasurethesample'sabsorptionofRFArecordertoplottheoutputfromthedetectorversustheappliedmagneticfield.TheChemicalShift化学位移ThevariationsinthepositionsofNMRabsorptions,arisingfromTheChemicalShift化学位移ThevariationsinthepositionsofNMRabsorptions,arisingfromelectronicshieldinganddeshielding,arecalledchemicalshifts.Thedifference(inpartspermillion)betweentheresonancefrequencyoftheprotonbeingobservedandthatoftetramethylsilane(TMS).Chemicalshiftsaremeasuredinpartspermillion(ppm).Bycustom,thedifferenceismeasuredingauss,butinfrequencyunits(hertzorυυ-SX106X0其中：υS样品信号频率；υTMS四甲基硅烷的信号频率；υ0Thesignalfromtetramethylsilane(TMS)isdefinedas0.00ppmontheδTheChemical化TheChemical化学位TheChemical化学TheChemical化学位ChapterNuclearChapterNuclearmagneticTheChemicaIShift化学位移TheChemicalShiftTheChemicalShiftofVinylandAromaticInbenzeneanditsderivatives,thearomaticringofpibondingelectronsactsasaconductor,andtheexternalmagneticfieldinducesaringcurrent.Atthecenterofthering,theinducedfieldactstoopposetheexternalfield.Theseinducedfieldlinescurvearound,however,andontheedgeoftheringtheinducedfieldaddstotheexternalfield.Asaresult,thearomaticprotonsareactuallydeshielded,resultinginabsorptionatlowvaluesoftheappliedmagneticBenzeneabsorbsBenzeneabsorbsat7.2,andmostaromaticprotonsabsorbintherangeof7toTheChemicalTheChemicalShiftofVinylandAromaticThepielectronsofanalkenedeshieldthevinylprotonsinthesamewaythatanaromaticringofelectronsdeshieldsthearomaticprotons.同芳香环，烯烃的πThemotionofthepielectronsgeneratesaninducedmagneticfieldthatopposestheappliedfieldatthemiddleofthedoublebond.Thevinylprotonsareontheperipheryofthisfield,wheretheinducedfieldbendsaroundandreinforcestheexternalfield.Asaresultofthisdeshieldingeffect,mostvinylprotonsabsorbintherangeof5to烯烃π电子的运动产生的感应磁场在双键的中心位置与外界磁场相反，而乙烯质子在吸收出现在（δ值）56AcetylenicHydrogensAcetylenicHydrogens乙炔氢Acetylenichydrogensabsorbaround乙炔氢的吸收在δ=2.5Asthemoleculestumbleinsolution,insomeorientationsthiscylinderofelectronscancirculatetoproduceaninducedmagneticfield.圆筒形πTheacetylenicprotonliesalongtheaxisofthisinducedfield,whichisashieldedregion.Whenthisshieldedorientationisaveragedwithallotherpossible(mostlydeshielded)orientations,theresultisaresonancearoundδ2.5.去屏蔽作用平衡后，得到乙炔氢的吸收位置在δ2.5TheChemicalShiftTheChemicalShiftofAldehydeThealdehydeprotonisdeshieldedbothbythecirculationoftheelectronsinthedoublebondandbytheinductiveelectron-withdrawingeffectofthecarbonyloxygenatom.Aldehydeprotons(-CHO)absorbbetween9and10.由于双键的去屏蔽化和氧原子的吸电子作用使得醛氢的吸收发生9与10Hydrogen-BondedProtons氢键质子ThechemicalshiftsofO-HprotonsinalcoholsandN-HprotonsinaminesdependontheHydrogen-BondedProtons氢Hydrogen-BondedProtons氢键质子Inconcentratedsolutions,theseprotonsaredeshieldedbyhydrogenbonding,andtheyabsorbatarelativelylowfield:aboutδ3.5foranamineN-Handaboutδ4.5foranalcoholO-H.3.5，Indilutesolutions,thesesignalsareobservedaroundδCarboxylicAcidProtons羧酸质子Becausecarboxylicacidprotonsarebondedtoanoxygennexttoacarbonylgroup,theyhaveconsiderablepositivecharacter.Theyarestronglydeshieldedandabsorbatchemicalshiftsgreaterthanδ10.δ10化学位移：δ羧酸质子>酮a-烷烃TheNumberTheNumberofSignals信号数目Ingeneral,thenumberofNMRsignalscorrespondstothenumberofdifferentkindsofprotonspresentinthemolecule..Protonsinidenticalchemicalenvironmentswiththesameshieldinghavethesamechemicalshift.Suchprotonsaresaidtobechemicallyequivalent.些质子是化学等价NuclearmagneticInsomecases,NuclearmagneticInsomecases,theremaybefewersignalsintheNMRspectrumthantherearedifferenttypesofprotonsinthemolecule.ProtonsthatarenotchemjcallyequivalentbuthappentoabsorbatthesamechemicalshiftaresaidtobeaccidentallyAreasofAreasoftheTheareaunderapeakisproportionaltothenumberofhydrogenscontributingtothatpeak.Methyltert-butyletherhasthreemethylhydrogensandninetert-butylhydrogens.Eachsimplyshowsthataboutthreetimesasmanyhydrogensarerepresentedbythepeakatδ1.2asarerepresentedbythepeakatδ3.2.AreasoftheAreasofthePeaks峰面TheareaunderapeakisproportionaltothenumberofhydrogenscontributingtothatTheintegratorhasmovedatotalof6spacesverticallyinintegratingthe12protonsinmolecule.EachprotonisrepresentedSpin-SpinASpin-SpinAprotonintheNMRspectrometerissubjectedtoboththeexternalmagneticfieldandtheinducedfieldoftheshieldingelectrons.Ifthereareotherprotonsnearby,theirsmallmagneticfieldsalsoaffecttheabsorptionfrequenciesoftheThissplittingofsignalsmultiplets,calledspin-spinsplitting,resultswhentwodifferenttypesofprotonsarecloseenoughthattheirmagneticfieldsinfluenceeachother.SuchprotonsaresaidtobemagneticallySpin-SpinSplitting自旋-Spin-SpinSplitting自旋-Spin-spinsplittingisareciprocalproperty.Thatis,ifoneprotonsplitsanother,thesecondprotonmustsplitthefirst.TheN+1Ingeneral,themultiplicity(numberofpeaks)ofanNMRsignalisgivenbytheN+1rule:IfasignalissplitbyNneighboringequivalentprotons,itissplitintoN+1N+1N1规则：如果一个信号被NSpin-SpinSpin-SpinTheRangeofMagneticCouplingTheRangeofMagneticCouplingMostspin-spinsplittingisbetweenprotonsonadjacentcarbonatoms.Bondedtothesamecarbon:twobondsbetweenprotonsspin-spinsplittingisnormallyobservedifnonequivalentBondedtoadjacentcarbons:threebondsbetweenprotonsspin-spinsplittingisnormallyobserved.Bondedtononadjacentcarbons:fourormorebondsbetweenprotonsspin-spinsplittingisnotnormallyobservedNuclearmagneticCouplingconstantsNuclearmagneticCouplingconstantsThedistancebetweenthepeaksofamultiplet(measuredinhertz)iscalledthecouplingconstant,whichcanprovideadditionalstructuralinformation.RepresentedbyJ,andthecouplingconstantbetweenHaandHbisrepresentedbyJHb间的耦合常数表示为Multipletsthathavethesamecouplingconstantmayarisefrom