核磁共振图谱解析解析NMR.ppt

NMR:原子核间的相互作用江南大学超值-划算--购物推荐群：302284607C-13spectraElectronegativity,hybridization,andanisotropyallaffect13Cchemicalshifts.
Theelectronegativeelementproducesalargedownfieldshiftsincetheelectronegativityatomisdirectlyattachedtothe13Catom.B.Calculationof13CChemicalShiftsSpin-SpinCoupling同核J-偶合(HomonuclearJ-Coupling)Ha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.Haproton-coupledspectra(nondecoupledspectra)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
Proton-Decoupled13CSpectra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[(w-J/2)+(w+J/2)]/2=w。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。NuclearOverhauserEnhancement(NOE)ThemaximumenhancementCross-polarizationNOEsaresometimesusedtoverifypeakassignments.4-2.6ProblemswithIntegrationin13CSpectra4-2.7MolecularRelaxationProcessT2≤T1,spin=1/2andasolventoflowviscosity,T2andT1areusuallyverysimilar.Toobtainadecentspectrumofthiscompound,itwouldbenecessarytoextendthedataacquisitionanddelayperiodssoastodeterminetheentirespectrumofthemoleculeandseethecarbonswithhighT1values.4-2.10SomeSampleSpectra-EquivalentCarbonsFig.4-2.9Theproton-decoupled13CNMRspectrumofcyclohexanolFig.4-2.10TheProton-decoupled13CNMRspectrumofcyclohexeneFig.4-2.11TheProton-decoupled13CNMRspectrumofcyclohexanone.4-2.11CompoundswithAromaticRingsFig.4-2.12TheProton-decoupled13CNMRspectrumoftoluene.AsymmetricallydisubstitutedPolysubstitution4-2.11C-13NMRSolvents-HeteronuclearCouplingofCtoDeuteriumExample4-2.1C3H6O2Example4-2.2C4H10OC5H8O2,anesterC7H8OC8H8ODEPT极化转移技术DEPT：区分13C的级数Fig.4-2.8(a)Standare13CdecoupledspectrumofipsenolinCDCl3,at75.5MHz.(b)DEPTsubspectra:DEPT135ºCHandCH3up.CH2down.(C)DEPT90ºCHonly.DEPT区分碳的级数4-3.2TheMechanismofCouplingA.One-BondCouplings(1J)2J,twobondcouplings,geminalcoupling,JgemFig4-3.3Thedependenceofthemagnitudeof2JHCH,thegeminalcouplingconstant,ontheHCHbondan