Benzene induced magnetic field

Annulene shows two signals in its NMR spectrum one at 9.25 ppm and the other very far upfield (beyond TMS) at —2.88 ppm. What hydrogens are responsible for each of the signals Hint Notice the direction of the induced magnetic field outside and inside the benzene ring in Figure 14.9.)... 

The induced magnetic field of the TT electrons of (a) ethylene and (b) benzene reinforces the applied field in the regions near vinyl and aryl protons and deshields them. 

The TT electrons in alkenes, alkynes, benzene, and others ir-bonded groups also circulate so as to generate an induced local magnetic field in the presence of an external magnetic field. Whether shielding or deshielding occurs depends on the location of the protons in the induced magnetic field. 

The circulation of tt electrons in benzene creates an induced magnetic field that, at the position of the protons, reinforces the applied magnetic field. This reinforcement causes the protons to be strongly deshielded and to have a relatively high frequency (S 7) absorption. 

FIGURE 14.8 The induced magnetic field of the TT electrons of benzene deshields the benzene protons. Deshielding occurs because at the location of the protons the induced field is in the same direction as the applied field. 

Ring currents (dotted lines) induced by an external magnetic field Bq induce magnetic fields in benzene, which add to the external field outside the ring and oppose it inside, above and below. 

The circulation of tt electrons in benzene creates an induced magnetic field that, at... 

B and N has an impact to the chemical bonding pattern and on electron delocalization. Owing to the stronger varying potential, the induced magnetic field is weaker than that of benzene, but nevertheless pronounced and long-ranged. 

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