1、Chapter 11 Spectroscopy（波谱）,11.1 Introduction(A) The instrumental Methods of structure determination to organic compounds(B) Property of electromagnetic radiation(C) Relationship between the molecular structure and absorption spectrum 11.2 Infrared spectroscopy (A) Infrared Spectroscopy (IR)(B) Mode
2、s of molecular vibrations(C) Factors to affect frequency of molecular stretching vibration and its location in an IR spectrum,(D) Treatment of the sample (E) Interpreting of IR spectra 11.3 Nuclear Magnetic Resonance (NMR) Spectroscopy 11.4 Shielding and deshielding of protons 11.5 The chemical shif
3、t11.5.1 The chemical shift11.5.2 The relation of molecular structure with 1H chemical shift11.5.3 Interpretting 1H NMR spectraDiastereotopic hydrogensEnantiotopic hydrogens,11.6 Signal splitting: spin-spin couplingCoupling constant nJabSplitting role (n + 1)roleReciprocity of coupling constantsSplit
4、ting patterns 11.7 13C NMR Spectroscopy11.7.1 Introduction The function of 13C NMR The great advantage of 13C spectroscopyDecoupling techniques11.7.2 13C chemical shiftsThe factors that most affect 13Cchemical shifts,(A) The principal instrumental methods of structure determination to organic compou
5、nds,Nuclear Magnetic Resonance Spectroscopy 核磁共振谱,Infrared Spetroscopy 红外光谱,IR,Key functional groups,Ultraviolet-Visible Spectroscopy 紫外可见光谱,UV-VIS,Electron distribution in the Mole. With Conjugated systems,Mass Spectrometry 质谱,MS,Molecular weight and Formula of the mole. and the structure units in
6、it.,1. Carbon skeleton 2. The Environments of the hydrogens atta-ched to carbon or other atoms,NMR,(B) Property of electromagnetic radiation:,E= h = hc/ h Planck s constant: 6.63 10-34 J. s Frequency( Hz), = c Wavelength (nm) c The speed of light: 3 10 8 m. s-1 The wave counts /cm,The properties of
7、both particles and waves,The greater the frequency, the shorter the wavelength; The shorter the wavelength, the higher the energy.,Ch.P153,h = E = E2 - E1,(C) Relationship between the structure of Mole. and absorptionspectrum:,Electronic energyUV-VIS Vibrational energy IR The spin states of an atomi
8、c nucleusNMR,11.2 Infrared spectroscopy (IR),Function of Infrared Spectroscopy:,Identifying the presence of certainfunctional groups in the molecules.,Electromagnetic spectrum,Electromagnetic radiation:,The compound absorb IR energy to causethe change of vibrational energy states of the covalent bon
9、d in the mole.,Ch.P154,B. Modes of molecular vibrations,Biatomic molecule,Triatomic molecule,An in-plane bending vibration,An out-of-plane bending vibration,A stretching vibration,Symmetricstretching,Asymmetric stretching,(C) Factors affecting frequency of molecularstretching vibration and its locat
10、ion in an IR spectrum,1. The masses of the bonded atoms:,Light atoms vibrate at higher frequencies,2. The relative stiffness of the bond (键的刚性）,(D) Treatment of the sample:,Neat sample: pure liquid betweentwo NaCl disks Solid: mixed with KBr and pressed intoa thin wafer Solution: CCl4, chloroform as
11、 solvent,(E) Interpreting of IR spectra:,16004000 cm-1 The region in which vibrationsof functional groups,1300625 cm-1 Fingerprint region,Characteristic absorptionsof the compounds,Ch.P519,Table 1 Infrared Absorption Frequencies of Some Common Structural Units,Stretching vibrations,Bending vibration
12、s of diagnostic value,CH3(CH2)6CH3,2960cm-1 2930cm-1 1467cm-1 1380cm-1,ArH (stretch),CH ( bending),Toluene,2-Methyl-2-propanol,OH (stretch),(E)-2-己烯,(Z)-3-己烯,2-甲基-1-丙烯,1-己炔,2-己炔,Essential condition of NMR:,The different Nuclei, the different E,11.3 Nuclear Magnetic Resonance （NMR） Spectroscopy,The s
13、pinning atomic nuclei: 1H, 13C (I= 12),Process of Nuclear Magnetic Resonance,Schematic operation of an NMR spectrometer,At the proton, the induced magnetic field opposes The external magnetic field,11.4 Shielding and deshielding of protons,Heffect = H0 - Hin,11.5.1 The chemical shift,The shift of ab
14、sorption signal of protonby shielding and deshileding effect.,Reference compound: (CH3)4Si, TMS,The chemical shift is expressed in hertz,The chemical shift is different with differentexternal magnetic field strengths.,Independent of the field strength,ppm: part per million 百万分之一,11.5.2 Relation of m
15、olecular structure with 1H chemical shifts:,Different environments of protons in the mole., different degrees of shielding in the experiment, different chemical shifts.,Increased shielding of methyl protons Decreasing electronegativity of attached atom,Aromatic protons are in the deshielding region.
16、,11.5.3 Intepreting proton NMR spectra(氢谱的解析),Information about the mole. Structure by1H NMR spectra:,The induced magnetic field oftheelectrons of an arenereinforces the applied fields.,磁各向异性效应,The number of signalsthe kind of proton; 2. Intergration of the area under each peakrelative ratios of dif
17、ferent protons; 3. Splitting of each signalnumber of vicinal protons to that one.,Ch.P164,CH3OCH2CN,Chemical nonequivalent,H1:H2 2:3,How many signals onNMR spectra?,Diastereotopic非对映异构,Enantiotopic hydrogen:,Enantiomers,CH2Br: The same ,Geminal protons,Ch. P165: Table 7-4,P424 Tab.13.3,1H NMR: can b
18、e in the range of 1-10 ppm,P423,11.6 Signal splitting: spin-spin coupling,CHCl2CH2Cl,The phenomenon of signal splitting is spin-spin splitting.,Singnal from the proton of Ha in the absence of Hb,Magnetic moments of Hb split the signal from Ha into two peaks of equal intensity, a 1:1 doublet.,Signal
19、splitting,The protons on neighboringatoms,Magnetic fields,The interaction of the nuclear Spins of neighboring atoms is called spin-spin coupling.,nJabcoupling constant(Hz),Distance,Independence of the field strength.,3JHH = 7.5Hz,Vicinal coupling,Signal splitting is not observed for protons:,Chemica
20、lly equivalent protons,2. Enantiotopic protons,3. Separated by more than three bonds,CH3CH3,Singlet Doublet Triplet Quartet,1:1 1:2:1 1:3:3:1,Multiple Broad: complex OH,When protons have the same chemical shifts, no signal splitting,Two groups of protons coupled to each other have the same coupling
21、constant J.,(proton of Hb split the signal into 1:3:3:1quartet),Multiplicity of signal for Ha = n + 1:,n quivalent protons on neighboring atoms,split a signal into n + 1 peaks.,(signal in the absence of protons Hb),Splitting role (n + 1)role :,P425, Ch.P165,CH3CH2Br,Reciprocity of coupling constants
22、,Integration:2:2:3,Problem 1. Describe the appearance of the 1H NMR spectrum,Isopropyl chloride,1H NMR(CDCl3) ,1.52 (d, J = 3.5Hz, 6H, CH3),4.2(m,1H,CHCl),Signals may overlap:,Splitting patterns,A. Doublet:,Nonequivalent vicinal protons, / J 6,First order spectrum:(n+1), / J 6,B. Two bond coupling,G
23、eminal protons,Diastereotopic,Different chemical shifts,doublet,doublet,2J = 2Hz,1-Chloro-1-cyanoethene,C. Complex Splitting,Doublet of doublet :dd,trans,cis,J trans Jcis,13C NMR spectrum directly provide the information about carbon skeleton of a molecule.,ClCH2CH2CH2CH2CH3,1H NMR 4 Signals,The nat
24、ural abundance:1 H 99.985%13C 1.1%12C 99%,Carbon isotopes,Pulse FT techniques (脉冲 傅立叶变换技术),Routine tool,The function of 13C NMR,P430 13.12,13C NMR 5 Signals,The great advantage of 13C spectroscopy,R,: 1H spectra: 3 ppm13C spectra: 8090 ppm,Peaks arising from all the carbon atoms.,(2) Signals are les
25、s likely to overlap.,13C spectra were further simplified,Spin-spin coupling between the carbon nuclei could be not seen.,(1) The wide range of chemical shifts,1H NMR spectrum: 012 ppm 13C NMR spectrum 0200 ppm,1) Broad band decoupling (宽带去耦),2) Proton off-resonance decoupling(偏共振去耦）,Decoupling techn
26、iques,Ch.P168,Broad band decoupling,Proton off-resonance decoupling,3) DEPT(Distortionless Enchancement by Polarization Transfer, 不失真地极化 转移增强）technique,11.7.2 13C chemical shifts,In most 13C spectra, the areas under signals are not proportional to the atoms causing the signals.,The 13C chemical shif
27、ts are importantdata to determine the structures of molecules.,P430 Fig. 13.17,The factors that most affect 13Cchemical shifts,2. The electronegativity of the group attached to carbon,1. The hybridization of carbon,(ppm): sp2 sp sp3,Problems to Chapter 11,P434 13.19(a), (e)CH3CH2CH2COCOOCH3 13.30(a),(c) 13.31(b) 13.34 13.35 13.36 13.39(c) 13.40,13.41 13.43 13.49 13.50 13.51 13.52,
