有机波谱分析双语课程 (23).pdf

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1、核磁共振碳谱 II 有机波谱分析 Organic Spectroscopic Analysis 13C NMR Spectroscopy II 2 13C Chemical shift 化学位移化学位移 范围：0-230 ppm 同样以TMS做内标 影响其化学位移的因素与1HNMR相同 3 Typical 13C NMR 1.Number of Different Carbons 不同碳的数目 2.Chemical Type of Carbons 碳的类型 Not always quantitative 一般没有定量关系 4 Common decoupling methods for 13C

2、NMR 1.Proton Broad Band Decoupling 2.Off-Resonance Decoupling 3.DEPT(Distortionless Enhancement of Polarisation Transfer)4.selective proton decoupling spectrum,SPD 5.Gated Decoupling 6.Inverted Gated Decoupling 中南民族大学 Li Tingcheng 5 中南民族大学 Li Tingcheng 5 Proton-decoupled carbon-13 NMR spectrum of 2-

3、butanol.中南民族大学 Li Tingcheng 6 中南民族大学 Li Tingcheng 6 1H-coupled carbon-13 NMR spectrum of 2-butanol.Off-resonance decoupling（偏共振去偶）(n+1 rule)Only the one bond coupling retained 7 Factors Influencing Chemical Shifts 1.Electronegativity deshielding 2.Anisotropy(due to magnetic fields generated by bonds

4、)3.Conjugation Effect 4.Hydrogen Bonding 5.Steric Effect 6.Solvent Effect 8 1.Hybridization sp3 Hybrid CH3 0 60 sp Hybrid CCH 60 90 sp2 Hybrid CHCH2 100 200 sp2 Hybrid C=O 150 220 2.Electronegativity induction effect C-F C-Cl C-Br C-I C,-C chemical shift to downfield.C to upfield because of steric e

5、ffect.Factors Influencing Chemical Shifts 9 2.Electronegativity induction effect X CH2 CH2 CH2 CH2 CH2 CH3 X=H X=I X=Br X=Cl X=F 14.2 7.0 33.9 45.2 84.3 23.1 34.0 33.3 33.1 30.9 32.2 30.7 28.4 27.1 25.4 32.2 31.3 31.5 31.7 32.2 23.1 23.1 23.1 23.1 23.1 14.2 14.2 14.2 14.2 14.2 10 3.Heavy atom effect

6、 After the substitution of heavy halogen atom iodine-I,the value of C is reduced,because there are a large number of electrons outside the I atom,which has a strong shielding effect on the C connected to it.4.Conjugation effect The effect of uneven distribution of electrons due to conjugation,which

7、shifts the value of C toward a up or down field.In the ortho position of C=O,an unsaturated bond or hetero atom is introduced to form a conjugated system.The density of the electron cloud on C=O carbon increases,and the shielding effect moves to a upfield.11 5.Steric effect Conjugation Effect OOO201

8、.6 192.4 190.7 OOO195.7 199.0 205.5 =0 =28 =50 OOO206.9 211.7 215.5(H 3 C)3 O H(H 3 C)3 O H 21.0 71.1 25.7 76.6 12 5.Steric effect:C separated by several bonds may have a strong influence due to the steric structure.Van der Waals is pushed away from the outer C to the vicinity of the opponents core,

9、and the c moves to upfields.6.Degree of substitution The number of substituents on C increases,and moves to the lower field.7.Electron deficiency effect C has a positive charge(lack of electrons),the shielding effect is reduced,and is in a low field.13 8.Hyperconjugation Effect.The phenomenon of-car

10、bon atoms shifting to upfield due to heteroatoms(such as N,O,Cl,etc.)connected to the second period is called the hyperconjugation effect.9.Hydrogen Bonding 10.Forming Hbond(deshielding effect)makes shift to lower field.oHoHoHoooH191 196 195 204 14 10.Matrix Effect 1)Solvent Effect 2)Dilution Shift：

11、In the same solvent,some compounds have higher chemical shift values at dilute concentrations than at high concentrations.Measurement of Spectrum with High Quality Nowadays almost all NMR data are acquired by the pulsed FT method.In this method,the consideration of the spin-lattice relaxation times(

12、T)of the signals of interest,i.e.,proper selection of the flip angle(pulse width)of the observed pulse and the pulse repetition time is of primary importance for quantitative analysis.15 Effects of Operating Conditions Effects of Operating Conditions 16 17 Measurements of NMR spectra under air great

13、ly decrease T1,particularly in the case of low molecular weight compounds.18 It is desirable to take the spectrum with as many accumulations as possible unless signal saturation does not occur 19 20 Interpretation and applications of 13C NMR 13C-NMR is used for compound structure analysis and reacti

14、on mechanism research.The number of carbon atoms,the number of hydrogen atoms on the carbon atoms,the chemical environment of the carbon atoms and the possible linking groups can be determined.21 NMR DATABASE Spectral Database for Organic Compounds（SDBS）http:/riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cr

15、e_index.cgi?lang=eng 13C-NMR spectrum analysis is usually carried out according to the following steps:1.Calculate the degree of unsaturation;2.Analyze the broadband decoupling spectrum,and analyze the sp3,sp2,sp hybridized carbons from the value of each peak(this judgment should be consistent with

16、the calculation of unsaturation)3.Benzene ring,double bond,triple bond,carbonyl,C-O,C-N.?4.The number of hydrogens connected to different carbons in each chemical environment was analyzed by Off-Resonance Decoupling/DEPT spectrum.5.Deduce the structure and carry out the necessary verification.Interpretation and applications of 13C NMR