/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