Magnetic field ring current

Aromatic ring currents[45, 46] or the charge stiffness[47] provide a related application of correction vectors, now associated with magnetic fields. Ring currents are the diamagnetic susceptibility of 4n+2 systems. The correction vector in monocycles is obtained from... 

As already mentioned, the application of H chemical shifts for the estimation charge density (KH) is not straightforward. The chemical shifts, (8N), considered should represent values which have been corrected for the influence of the induced magnetic fields (ring-current effect). From carbon chemical shifts, which are insensitive to ring current effects along the perimeter of the molecule, the local charge densities, qn can be estimated (Eq. 6) ... 

The electromotive force induced in one ring probe is caused by a change with time of the magnetic field of the current in the ring located in a free space as well as by the magnetic field of currents induced in a conducting medium. Thus ... 

FIGURE 13 10 More shielded (red) and less shielded (blue) protons in (a) [18]annulene and (b) [16]annulene The induced magnetic field associated with the aromatic ring current in [18]annulene shields the inside protons and deshields the out side protons The opposite occurs in [16]annulene which is antiaromatic... 

Figure 15.14 The origin of aromatic ring-current. Aromatic protons are deshielded by the induced magnetic field caused by delocalized tt electrons circulating in the molecular orbitals of the aromatic ring.

Induced magnetic field because of ring current... 

Ring current (Section 15.8) The circulation of tt electrons induced in aromatic rings by an external magnetic field. This effect accounts for the downfield shift of aromatic ring protons in the lH NMR spectrum. 

Magnetic criteria of aromaticity are based on the model of interatomic teratomic ring currents induced in conjugated cyclic molecules by external magnetic fields. 

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