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1、核磁共振氢谱 II 有机波谱分析 Organic Spectroscopic Analysis 1H NMR Spectroscopy II 2 Bo(1-)sigma-depends on density of electronsaround nucleusOrigin of the three peaks:Chemical Shift effective0000BBBBBB(1)Shift in ,due to shielding by electrons,is called the 60 MHz NMR spectrum of CH3CH2OH 60,000,000 Hz 60,000,
2、220 Hz 60,000,320 Hz 60,000,072 Hz CH3Si CH3CH3CH3(parts per million)effective0000BBBBBB(1)4 Field Dependence This difference will also depend on the strength of the applied magnetic field,B0.The greater the value of B0,the greater the frequency difference.CH3Br 60MHz(Bo=14100)=162 Hz 100MHz(Bo=2350
3、0)=270 Hz 5 Field Dependence 6 To correct the effect of Bo,Chemical shift of sample was compared with a standard TMS(tetramethyl silane)Chemical Shift Chemical Shift:=(sample-STD)/STD 106 (ppm)7 Factors Influencing Chemical Shifts 1.Electronegativity deshielding 2.Anisotropy(due to magnetic fields g
4、enerated by bonds)3.Conjugation Effect 4.Hydrogen Bonding 5.Steric Effect 6.Solvent Effect 8 Factors Influencing Chemical Shifts 1Electronegativity deshielding-CH3，=1.62.0，High Field-CH2I，=3.0 3.5,-O-H，-C-H，big small Low Field High Field 9 How does electronegativity influence chemical shift?Proton C
5、hemical Shifts Compound(CH3)4C(CH3)3N(CH3)2O CH3F 0.9 2.1 3.2 4.1 Compound(CH3)4Si(CH3)3P(CH3)2S CH3Cl 0.0 0.9 2.1 3.0 Cpd./Sub.X=Cl X=Br X=I X=OR X=SR CH3X 3.0 2.7 2.1 3.1 2.1 CH2X2 5.3 5.0 3.9 4.4 3.7 CHX3 7.3 6.8 4.9 5.0 Factors Influencing Chemical Shifts(1)10 Factors Influencing Chemical Shifts
6、(2)-bonds induced circular current Induced filed-bonds induced circular current Induced filed Applied field Applied field Deshielding effect 2.Anisotropic effect 11 Anisotropic effect-bonds induced circular current Induced field Applied field Deshielding effect Shielding effect 12 Anisotropic effect
7、-bonds in benzene induced circular current 13 3.Hydrogen Bonding Hydrogen bonding shifts the resonance signal of a proton to lower field(higher frequency)Factors Influencing Chemical Shifts(3)14 4.Steric Effect(deshielding）HCOH3CCOCH3HOHHHHO 3.75 1.77 2.31 3.5515 5.Van der Waals-deshielding Ha=3.92p
8、pm Hb=3.55ppm Hc=0.88ppm Ha=4.68ppm Hb=2.40ppm Hc=1.10ppm HCHbHaOHHCHbHaHO0.883.553.921.104.682.40(A)(B)中南民族大学 Li Tingcheng 16 Solvent Effect 17 Summary 1.Electronegativity deshielding 2.Anisotropy(due to magnetic fields generated by bonds)3.Conjugation Effect 4.Hydrogen Bonding 5.Steric Effect 6.So
9、lvent Effect 18 Typical Chemical Shifts of Organic Compounds AlkaneAlkane -CH3:CH3=0.79 1.10ppm-CH2:CH2=0.98 1.54ppm-CH:CH=CH3+(0.5 0.6)ppm O CH3N CH3C CH3C CH3OCCH3 H=3.24.0ppm H=2.23.2ppm H=1.8ppm H=2.1ppm H=23ppm Chemical ShiftChemical Shift 19 烯烃烯烃 Terminal group：H=4.85.0ppm middle group：H=5.15.
10、7ppm conjugation with C=C and aromatics:H=47ppm Aromatic hydrocarbonAromatic hydrocarbon Aromatic hydrocarbon：H=6.58.0ppm Benzene H=7.3ppm Electron withdrawing group substitution-OR，-NR2 时：时：H=6.57.0ppm Electron donating group substitution-COCH3，-CN，-NO2 时时：H=7.28.0ppm Chemical ShiftChemical Shift T
11、ypical Chemical Shifts of Organic Compounds 20-COOH：H=1013ppm-OH：（Alcohol）H=1.06.0ppm （Phenol）H=48ppm-NH2：（Fatty amine）H=0.43.5ppm （Aromatic amine）H=2.94.8ppm （Amide）H=9.010.2ppm -CHO：H=910ppm Chemical ShiftChemical Shift Typical Chemical Shifts of Organic Compounds 21 Characters of active protons T
12、he exchange rate of active protons：OH NH SH，has a wide range.22 Chemical Shift 23 ChemNMR Draw your structure of interest with ChemDraw then predict 13C and 1H NMR chemical shifts with the ChemNMR tools.In case of 13C NMR,over 95%of the shifts can be predicted with a mean deviation of 3.8 ppm.In cas
13、e of 1H NMR,shifts of about 90%of all CHx-groups can be predicted with a mean deviation of 0.2-0.3 ppm.各类质子的化学位移经验计算各类质子的化学位移经验计算 ChemNMR 24 NH2CCH3HaHbHcHdNHHHH8.577.297.692.598.571.2425 ChemNMR But the use of polar solvents may strongly increase these deviations.1H NMR shifts of hydrogen atoms bonded to hetero atoms are not predicted because they are affected by solvents,concentration,impurities and steric effects.