高分子材料研究方法核磁共振与电子顺磁共振波谱法.ppt
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1、Chap 3 NMR Spectroscopy and EPR Spectroscopy,3.1 Introduction3.2 1H NMR Spectroscopy3.3 13C NMR Spectroscopy3.4 EPR Spectroscopy3.5 Applications on Polymers,3.1 Introduction,Magnetism and SpinMagnetic ResonanceNMR SpectroscopyEPR Spectroscopy,3.1.1 Magnetism and Spin,MagnetismMoving charges generate
2、 magnetic fieldsThe magnetism of materials are related with the spin of microparticles,3.1.1 Magnetism and Spin,3.1.2 Magnetic Resonance,Magnetic Resonance,3.1.3 NMR Spectroscopy,3.1.3 NMR Spectroscopy,3.1.3 NMR Spectroscopy,Relaxation:excited nuclei return to the lower energy levels without radiati
3、onSpin-crystal relaxation:energy exchanged to surrounding particles/T1(half life)Spin-spin relaxation:energy exchanged with adjacent nucleus/T2(half life),3.1.4 EPR Spectroscopy,Unpaired electrons,3.2 1H NMR Spectroscopy,Chemical ShiftsSpin-Spin CouplingIntegral of Absorption PeakElucidation of 1H N
4、MR Spectra,3.2.1 Chemical Shifts,3.2.1 Chemical Shifts,The Shielding EffectHeff=H0(1-)=Heff/2Heff:the field experienced by the nucleus;H0:the external field(of the spectrometer);:the nondimensional shielding constant;:the frequency at which NMR transition occurs;:the magnetogyric ratio.,3.2.1 Chemic
5、al Shifts,The Shielding EffectShielding:H attached to an electron-donating substituent a decrease in HeffDeshielding:H attached to an electron-withdrawing group an increase in Heff,3.2.1 Chemical Shifts,Chemical Shifts=(sample-reference)/spectrometer 106(ppm)Normally,tetramethylsilane(TMS)is chosen
6、as the reference in non-aqueous media.In TMS,12 protons are all chemically equivalent and give a single peak at an H0 higher than most other proton resonances.,3.2.1 Chemical Shifts,Chemical ShiftsThe range of the 1H chemical shifts:rather small,0-15.H0 will not influence the 1H chemical shifts,3.2.
7、1 Chemical Shifts,Chemical ShiftsFactors influencing chemical shifts:The electronegtivity:The more electronegtive the atom which the carbon bearing the proton is attached to,the more deshielded the proton.,3.2.1 Chemical Shifts,Chemical ShiftsFactors influencing chemical shifts:The ring current of t
8、he delocalized electrons:magnetic anisotropyThe hydrogen bond:deshieldingThe solvent effect,similarly,3.2.1 Chemical Shifts,Chemical ShiftsSome empirical rules:For methene and methylene groups:=0.23+iFor 1H attached to alkenes:=5.23+Zgeminal+Ztrans+Zcis For substituent benzenes:=7.30-Si,3.2.2 Spin-S
9、pin Coupling,The Spin-Spin CouplingNuclei can interact with each other to cause mutual splitting of the otherwise sharp resonance lines into multiplets.The coupling constant:the spacing of the multiplets,which characterizes the strength of the coupling and is expressed in hertz.,3.2.2 Spin-Spin Coup
10、ling,The Origin of Spin-Spin Coupling1H has 2 orientations:If the orientation the adjacent proton with the magnetic field:absorb a slight higher frequencyIf the orientation the adjacent proton against the magnetic field:absorb a slight lower frequency,3.2.2 Spin-Spin Coupling,The EquivalenceThe chem
11、ical equivalence:The magnetical equivalence:The spin systemThe expression of non-equivalent 1H:A,B,ZThe expression of chemically equivalent 1H:AThe expression of magnetically equivalent 1H:AnThe strength of the spin-spin coupling system,3.2.2 Spin-Spin Coupling,The Splitting PatternsThe first-order
12、spectra/J 6Chemically and magnetically equivalent protons do not couple to one anotherCoupling with two groups of equivalent protons:the number of the multiplet n+1 rule/the relative intensities of which are given by Pascals triangle/the center of each group of the multiplet/J the distance between t
13、he splittings,3.2.2 Spin-Spin Coupling,The First-order SpectraCoupling with several groups of magnetically protons:the number of the multiplets:(n1+1)(n2+1)(nN+1)The Second-order Spectra/J n+1 rule/the relative intensities/:not at the center,but at the center of gravity/J:,3.2.2 Spin-Spin Coupling,T
14、he Coupling Constant and the Molecular StructureThe one bond(1J)coupling:13C-1HThe two bond(2J)coupling:the geminal coupling,J is the largest in 1H NMRThe three bond(3J)coupling:the vicinal coupling,the most common in 1H NMRThe four or five(4J or 5J)coupling:the long-range coupling,mainly occur in a
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- 高分子材料 研究 方法 核磁共振 电子顺磁共振 波谱
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