Benzene external magnetic field

FIGURE 2. Dependence of the products ratio 2/1 on the external magnetic field strength (Ho) observed for the reaction of benzyl chloride with Et3GeNa in benzene. The solid line shows the second order polynomial fit of the experimental data... 

Fig. 9-2. The observed linear relation between logS and [- log(l-F)] in the photodecomposition of DBK at room temperature in benzene and micellar HDTCL solutions in the absence and presence of an external magnetic field of 1.5 T. Here.HDCL indicates hexadecyltrimethyl-...

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. 

Figure 3. A representation of the circulation of n electrons of benzene under the influence of an external magnetic field (Ho). A secondary field is estabUshed. The secondary field opposes the external field in the center of the ring but reinforces it along the periphery where the protons he.

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. 

Figure 15-9 The 77 electrons of benzene may be compared to those in a loop of conducting metal. Exposure of this loop of electrons to an external magnetic field Ho causes them to circulate. This ring current generates a local field, reinforcing Ho on the outside of the ring. Thus, the hydrogens resonate at lower field.

One of the most typical features of benzene is that it sustains a so-called ring current [14]. When an external magnetic field is applied orthogonally to the benzene plane (henceforth always referred to as the z-axis), a ring current is induced which can to first order be written as the sum of two contributions, the first historically known as the paramagnetic term and the second one as the diamagnetic term. From... 

The presence of a ring current is invoked in aromatic molecules in the explanation of the exaltation and exceptional anisotropies observed in their magnetic susceptibilities and in the interpretation of NMR chemical shifts. The current induced by the application of an external magnetic field is a flow of electrons in physical space and its existence and properties are therefore real and determinable. Thus the display of the current given in Figure 13 provides a simple direct answer to the question as to whether or not a ring current is generated in benzene by a perpendicular field. 

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