Benzene ring current

The benzene ring current causes large shifts for aromatic protons... 

In conclusion, this brief summary of the equivalent dipole model of the benzene ring current and Its application to both Inter and Intra-molecular geometries has shown hopefully that this simple concept can be usefully applied to a variety of complex situations to gain detailed conformational Information. 

Something interesting happens when we go beyond benzene to apply the aromatic ring current test to annulenes... 

The presence of a ring-current is characteristic of all Hiickel aromatic molecules and is a good test of aromaticity. For example, benzene, a six-7r-clectron aromatic molecule, absorbs at 7.37 5, but cyclooctatetraene, an eight--iT-electxon nonaromatic molecule, absorbs at 5.78 8. 

Accordingly, the mechanism of conduction in metals is different from that for the ring currents in benzene, other aromatic molecules, and graphite, in which the atoms do not have the metallic orbital.16 16... 

Figure 5 The diamagnetic ring current effect in benzene.

Ring current (anisotropic) effects do not play a significant role in fluorine NMR. Therefore, fluorine substituents on a benzene ring absorb in the general region of fluoroalkenes, with fluorobenzene and 1-fluoronaphthalene having chemical shifts of -113.5 and -123.9 ppm, respectively. The fluorine NMR of fluorobenzene is shown in Fig. 3.14. 

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