核磁共振图谱解析解析NMR_精品文档优质PPT.pptx

1、购物推荐群：302284607302284607C-13 spectraC-13 spectra can be determine the number of nonequivalent carbons and to identify the types of C（CH3,CH2,aromatic,C=O）that may be present in a compound.C-13 NMR provides direct information about the carbon skeleton of a molecule.Electronegativity,hybridization,and

2、 anisotropy all affect 13C chemical shifts.The electronegative element produces a large downfield shift since the electronegativity atom is directly attached to the 13C atom.Fig.4-2.2 A Fig.4-2.2 A 1313C correlation chart for carbonyl and nitrile functional groups C correlation chart for carbonyl an

3、d nitrile functional groups 01234567891011（环）烷烃（环）烷烃 取代取代烷烃烷烃炔烃炔烃 单取代单取代烷烃烷烃 双取代双取代烷烃烷烃烯烯烃烃芳芳烃、杂芳环烃、杂芳环羧酸羧酸醛醛1H020406080100120140160180200220季碳季碳伯碳伯碳羰基羰基芳芳烃、杂芳环烃、杂芳环13C仲碳仲碳叔碳叔碳炔烃炔烃烯烯烃烃化学位移化学位移B.Calculation of 13C Chemical Shiftsm-xylene,the base value for the C in a benzene ring is 128.5 ppm.ipsoort

4、hometaparaCH38.90.7-0.1-2.9C1=base+ipso+meta=128.5+8.9+（-0.1）=137.3 ppmC2=base+ortho+ortho=128.5+0.7+0.7 =129.9 ppmC3=C1C4=base+ortho+para=128.5+0.7+（-2.9）=126.3 ppmC5=base+meta+meta=128.5+（-0.1）+（-0.1）=128.3 ppmC6=C4The observed values for C1,C2,C4,and C5 are 137.6,130.0,126.2 and 128.2 ppm.Spin-Sp

5、in CouplingCoupling Constants:Coupling Constants:n nJ J is a constant.is a constant.Homonuclear coupling,3J（1H-1H）=8Hz;heteronuclear coupling,1J（13C-1H）=156Hz;The electrons in the intervening bonds between the two nuclei transfer spin information from one nucleus to another by means of interaction b

6、etween the nuclear and electronic spins.CH异核J-couplingJCHCHHC同核 J-couplingJHH同核J-偶合（Homonuclear J-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:HaHbCCwawbJABHBHBHAHAJABHaHbCCHcAB,CBACAB,C是磁等价的核JAB=JAC同核J-偶合（Homonuclear J-Coupling）自旋-自旋偶合

7、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.CHJCHCHJCHoriginal frequencyww-J/2w+J/2JCH异核J-偶合（Heteronuclear J-Coupling）One-bond couplingsJ,100-250 HzHaHbCCHcB,C是化学不等价的核JAC=16 HzJAC=8 HzJBC=3 HzACBwAJACJAB同核J-偶合（Homonuclear J-Coupling）异核J-偶合（Heteronuclear J-Coupling）*CH*CH2*CH3CH1H2H3CH1H2CH1*CC由于一些

8、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-13C105 HzH-12C异核J-偶合（Heteronuclear J-Coupling）proton-coupled spectra（nondecoupled spectra）Fig.4-2.4 Ethyl phenylacetate.（a）The proton-coupled Fig.4-2.4 Ethyl phenylacetate.（a）The proton-coupled 1313C C spectrum.（b）The proton-decoupled sp

9、ectrum.（b）The proton-decoupled 1313C spectrumC spectrumQuartet,J=127 HzProton-coupled spectra for large molecules are often difficult to interpret.The multiplets from different C commonly overlap because the 13C-H coupling constants are frequently larger than the chemical differences of the C in the

10、 spectrum.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-Decoupled 13C SpectraThe decoupling technique obliterates all interactions between 13C-H;therefore,only singlets are observed in a decou

11、pled 13C NMR spectrum.The decoupler simultaneously irradiates a second,tunable radiofrequency which causes the protons to become saturated,and they undergo rapid upward and downward transitions,among all their possible spin states.These rapid transitions decouple any spin-spin interactions between 1

12、3C-H being observed.In effect,all spin interactions are averaged to zero by the rapid changes.The 13C“senses”only one average spin state for the attached Hs rather than two or more distinct spin states.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，

13、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。CHJCHCHJCHp-pulse on H这相当于使用一系列1800脉冲快速照射氢核。C-HpHC-HpHpHpHC-HC-HC-HC-HpHw w+J/2w w-J/2w+w+J/2w w-J/2w w+J/2w w-J/2去偶（Decoupling）Fig.4-2.5 The proton-decoupled Fig.4-2.5 The proton-decoupled 1313C spectrum of 1-propanolC spectrum of 1-propanol氢

14、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）Nuclear Overhauser Enhancement（NOE）The intensities of many of the C resonances in a proton-decoupled 13C spectrum increase significantly above those observed in a proton-coupled experiment.核核Overhauser效应效应（NOE）Overhauser等人

15、及以后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，偶极偶极相互作用自旋发生共振并达到饱和时，偶极偶极相互作用（弛弛豫豫）引起核自旋态分布变化，使得待观察的核的信号强引起核自旋态分布变化，使得待观察的核的信号强度增加。其空间作用距离度增加。其空间作用距离 CH2 CH CThe interaction of the spin-spin dipoles operates through space,not through bonds,and its magnitude decreases as a function of the inverse of r3（radial distance）.rNOEs are sometimes used to verify peak assignments.The syn methyl group is closer to the aldehyde hydrogen.Irradiation of the aldehyde H leads to a larger NOE for the carbon of the syn methyl group than for that of the anti methyl group,allowing the p