核磁共振图谱解析解析NMR

NMR:原子核间的相互作用分子中的原子并不是孤立存在,它不仅在相互间发生作用也同周围环境发生作用,从而导致相同的原子核却有不同的核磁共振频率.0BELarmor频率化学位移自旋-自旋偶合e.g.B0=11.7T,(1H)=500MHz(13C)=125MHz化学位移~B0kHz自旋-自旋偶合Hz-kHz江南大学超值-划算--购物推荐群：302284607C-13spectraC-13spectracanbedeterminethenumberofnonequivalentcarbonsandtoidentifythetypesofC(CH3,CH2,aromatic,C=O)thatmaybepresentinacompound.C-13NMRprovidesdirectinformationaboutthecarbonskeletonofamolecule.Electronegativity,hybridization,andanisotropyallaffect13Cchemicalshifts.Theelectronegativeelementproducesalargedownfieldshiftsincetheelectronegativityatomisdirectlyattachedtothe13Catom.Fig.4-2.2A13Ccorrelationchartforcarbonylandnitrilefunctionalgroups01234567891011（环）烷烃取代烷烃炔烃单取代烷烃双取代烷烃烯烃芳烃、杂芳环羧酸醛1H020406080100120140160180200220季碳伯碳羰基芳烃、杂芳环13C仲碳叔碳炔烃烯烃化学位移B.Calculationof13CChemicalShiftsm-xylene,thebasevaluefortheCinabenzeneringis128.5ppm.ipsoorthometaparaCH38.90.7-0.1-2.9C1=base+ipso+meta=128.5+8.9+(-0.1)=137.3ppmC2=base+ortho+ortho=128.5+0.7+0.7=129.9ppmC3=C1C4=base+ortho+para=128.5+0.7+(-2.9)=126.3ppmC5=base+meta+meta=128.5+(-0.1)+(-0.1)=128.3ppmC6=C4TheobservedvaluesforC1,C2,C4,andC5are137.6,130.0,126.2and128.2ppm.CH3CH3123456Spin-SpinCouplingCouplingConstants:nJisaconstant.Homonuclearcoupling,3J(1H-1H)=8Hz;heteronuclearcoupling,1J(13C-1H)=156Hz;Theelectronsintheinterveningbondsbetweenthetwonucleitransferspininformationfromonenucleustoanotherbymeansofinteractionbetweenthenuclearandelectronicspins.CH异核J-couplingJCHCHHC同核J-couplingJHH同核J-偶合(HomonuclearJ-Coupling)多重峰出现的规则:1.某一原子核与N个相邻的核相互偶合将给出(n+1)重峰.2.等价组合具有相同的共振频率.其强度与等价组合数有关.3.磁等价的核之间偶合作用不出现在谱图中.4.偶合具有相加性.例如:HaHbCCabJABHBHBHAHAJABobservedspincoupledspinintensityAB1B1BA1A1HaHbCCHcAB,CBACAB,C是磁等价的核JAB=JAC同核J-偶合(HomonuclearJ-Coupling)自旋-自旋偶合引起共振线的分裂而形成多重峰.多重峰实际代表了相互作用的原子核彼此间能够出现的空间取向组合.CHJCHCHJCHoriginalfrequency-J/2+J/2JCH异核J-偶合(HeteronuclearJ-Coupling)One-bondcouplingsJ,100-250HzHaHbCCHcB,C是化学不等价的核JAC=16HzJAC=8HzJBC=3HzACBAJACJAB同核J-偶合(HomonuclearJ-Coupling)异核J-偶合(HeteronuclearJ-Coupling)*CH*CH2*CH3CH1H2H3CH1H2CH1*CC由于一些核的自然丰度并非如此100%。因此谱图中可能出现偶合分裂的峰和无偶合的峰。氯仿中的氢谱是一个典型的例子。x100H-13CH-13C105HzH-12C异核J-偶合(HeteronuclearJ-Coupling)proton-coupledspectra(nondecoupledspectra)Fig.4-2.4Ethylphenylacetate.(a)Theproton-coupled13Cspectrum.(b)Theproton-decoupled13CspectrumQuartet,J=127HzProton-coupledspectraforlargemoleculesareoftendifficulttointerpret.ThemultipletsfromdifferentCcommonlyoverlapbecausethe13C-HcouplingconstantsarefrequentlylargerthanthechemicaldifferencesoftheCinthespectrum.原子核间的偶合导致谱图的复杂化(“精细裂分”)，灵敏度下降。如果峰数不多，偶合的方式仍可分析出。但当很多锋出现时，偶合方式的分析就不是那么容易。直接偶合:1J(13C,1H)~125-150Hz长程偶合:nJ(13C,1H)~1-10Hz*CH3-CH2-未去偶氢去偶去偶(Decoupling)Proton-Decoupled13CSpectraThedecouplingtechniqueobliteratesallinteractionsbetween13C-H;therefore,onlysingletsareobservedinadecoupled13CNMRspectrum.Thedecouplersimultaneouslyirradiatesasecond,tunableradiofrequencywhichcausestheprotonstobecomesaturated,andtheyundergorapidupwardanddownwardtransitions,amongalltheirpossiblespinstates.Theserapidtransitionsdecoupleanyspin-spininteractionsbetween13C-Hbeingobserved.Ineffect,allspininteractionsareaveragedtozerobytherapidchanges.The13C“senses”onlyoneaveragespinstatefortheattachedHsratherthantwoormoredistinctspinstates.氢对碳的偶合作用可以通过对氢施加一个脉冲消除。此一技术称为去偶。对氢核的饱和照射，促使氢核的自旋状态快速的变换，临近的碳核无法感觉到氢核的自旋状态的取向而只感受到氢核两种取想的平均效果。具体的说，对氢核的饱和照射使碳核原来的两条共振线w-J/2和w+J/2合并平均而得到[(-J/2)+(+J/2)]/2=。CHJCHCHJCHp-pulseonH这相当于使用一系列1800脉冲快速照射氢核。C-HpHC-HpHpHpHC-HC-HC-HC-HpH+J/2-J/2+J/2-J/2+J/2-J/2去偶(Decoupling)Fig.4-2.5Theproton-decoupled13Cspectrumof1-propanol氢去偶除简化碳谱还因为有核的Overhauser效应而增加信噪比。decoupledcoupledC-HC-H2*CH3-CH2-去偶(Decoupling)NuclearOverhauserEnhancement(NOE)TheintensitiesofmanyoftheCresonancesinaproton-decoupled13Cspectrumincreasesignificantlyabovethoseobservedinaproton-coupledexperiment.核Overhauser效应（NOE）—Overhauser等人及以后的研究人员发现，当核外电子自旋或相邻磁性核的核自旋发生共振并达到饱和时，偶极－偶极相互作用(弛豫)引起核自旋态分布变化，使得待观察的核的信号强度增加。其空间作用距离5~6Å。CwithHdirectlyattachedareenhancedthemost,andtheenhancementincreases(butnotalwayslinearly)asmoreHsareattached.ThemaximumenhancementTheNOEeffectisgeneral,showingupwhenoneoftwodifferenttypesofatomsisirradiatedwhiletheNMRspectrumoftheothertypeisdetermined.Theeffectcanbeeitherpositiveornegative,dependingonwhichatomtypesareinvolved.Inthecaseof13C-1H,theeffectispositive;irradiatingtheHincreasestheintensitiesoftheCsignals.998.1)28.675.267(211(max))(21maxmaxmax+NOENOEensityintpredictedtotalNOEobsirrCross-polarizationInH-decoupled13Cspectra,irradiatedH→saturated→adistributionofspinsverydifferentfromtheirequilibrium(Boltzmann)state.(morespinsthannormalintheexcitedstate)Duetotheinteractionofspindipoles,thespinsof13C“sense”thespinimbalanceofH,→begintoadjustthemselvestoanewequilibriumstate,morespinsinthelowerstate.excesspopulationInaH-decoupled13Cspectrum,thetotalNOEforagivenCincreasesasthenumberofnearbyHincreases.CH3CH2CHCTheinteractionofthespin-spindipolesoperatesthroughspace,notthroughbonds,anditsmagnitudedecreasesasafunctionoftheinverseofr3(radialdistance).H→Cr)1(=NOE3rfNOEsaresometimesusedtoverifypeakassignments.