清华大学：《生物核磁共振波谱学》课程教学资源（PPT课件，英文版）3 NMR Spectroscopy

/到 生物核磁共振波谱学 NMR in Biological science JUUL 3. NMR Spectroscopy THNMR AN

生物核磁共振波谱学 NMR in Biological Science 3. NMR Spectroscopy THNMR YAN

3. 1 Chemical shift When an atom is placed in a magnetic field, B its electrons circulate about the direction of the applied magnetic field. This circulation causes a small magnetic field at the nucleus which opposes the externally applied field The magnetic field at the nucleus(the effective field) is therefore generally less than the applied field by a fraction THNMR AN

3.1 Chemical Shift When an atom is placed in a magnetic field, its electrons circulate about the direction of the applied magnetic field. This circulation causes a small magnetic field at the nucleus which opposes the externally applied field. The magnetic field at the nucleus (the effective field) is therefore generally less than the applied field by a fraction . B = Bo (1-s) THNMR YAN

the methanol molecule B THNMR YAN

the methanol molecule THNMR YAN

the benzene molecule In some cases. such as the benzene molecule. the circulation of the electrons in the aromatic orbitals creates a magnetic field at the hydrogen nuclei which enhances the b. field This phenomenon is B called deshielding. In this example, the b. field is applied perpendicular to the plane of the molecule. The ring current is traveling clockwise if you look down at the plane THNMR YAN

In some cases, such as the benzene molecule, the circulation of the electrons in the aromatic orbitals creates a magnetic field at the hydrogen nuclei which enhances the Bo field. This phenomenon is called deshielding. In this example, the Bo field is applied perpendicular to the plane of the molecule. The ring current is traveling clockwise if you look down at the plane. the benzene molecule THNMR YAN

屏蔽常数σ和所处的化学环境有关 0,toot an:抗磁屏薇,与核外电子有关 n:顺屏,与核,电子有关 n:基回各身异性的影 a:溶介质的影响 THNMR YAN

屏蔽常数s 和所处的化学环境有关 s = sd + sp + sa + ss sd : 抗磁屏蔽，与核外s电子有关 sp : 顺磁屏蔽，与核外p,d电子有关 sa : 相邻基团各向异性的影响 ss : 溶剂、介质的影响 THNMR YAN

The electron density around each nucleus in a molecule varies according to the types of nuclei and bonds in the molecule. The opposing field and therefore the effective field at each nucleus will vary This is called the chemical shift phenomenon The chemical shift of a nucleus is the difference between the resonance frequency of the nucleus and a standard relative to the standard. This quantity is reported in ppm (parts per million) and given the symbol delta, memo: 8=(v-VREF X10/vREF Standard: TMS. DSS. etc THNMR YAN

The electron density around each nucleus in a molecule varies according to the types of nuclei and bonds in the molecule. The opposing field and therefore the effective field at each nucleus will vary. This is called the chemical shift phenomenon. The chemical shift of a nucleus is the difference between the resonance frequency of the nucleus and a standard, relative to the standard. This quantity is reported in ppm （parts per million) and given the symbol delta, memo: d = (n - n REF) x10 6 / n REF Standard: TMS, DSS, etc THNMR YAN

solvent dependence Ethanol-CDCI3 CH3 CH2. OH 109 Ethanol -D2O OH CH3 CH THNMR AN

solvent dependence THNMR YAN

ethanol in CdcL 3 ethanol in hoo 627T THNMR YAN

ethanol in CDCL3 ethanol in H2O THNMR YAN

3.2 Spin-Spin Coupling Nuclei which are close to one another exert an influence on each other's effective magnetic field This effect shows up in the NMr spectrum when the nuclei are nonequivalent If the distance between non-equivalent nuclei is less than or equal to three bond lengths, this effect is easy-observable This effect is called spin-spin coupling or j coupling THNMR AN

3.2 Spin-Spin Coupling Nuclei which are close to one another exert an influence on each other's effective magnetic field. This effect shows up in the NMR spectrum when the nuclei are nonequivalent. If the distance between non-equivalent nuclei is less than or equal to three bond lengths, this effect is easy-observable. This effect is called spin-spin coupling or J coupling. THNMR YAN

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