Shielding field

The Molecular Magnetic Shielding Field Response Graph Illustrations of the Benzene Field ... 

Numerical results for the shielding field of the benzene molecule are collected in Table 1 for the center of the molecule (labelled COM), and for points along a quarter circle of radius 2.47 A from the -ajcis to the x-axis, see Figure 3 for specification of axes. The radius of the circle corresponds to the distance from the ring center to a proton but, as defined, the points lie in the entirely nucleus-free xz-plane. Except for COM, the entries in the table are labelled by the angle between the z-axes and the direction to the field point. The table includes the isotropic part of the shielding, and the principal... 

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Therefore, the shielding field of the peripheral porphyrins influences even the central part of the template porphyrin. H NMR studies also show that the phenyl substituents are fixed in space they are perpendicular both to the Ru(II) porphyrin mean planes and the central, assembling, free-base porphyrin, forming the rims of a molecular box. In fact, the pentamer really plays the role of a molecular box when the central porphyrin is complexed with Zn(II) and is able to selectively recognize S-bonded Ru(II) complexes of Me.SO. 

Shift anisotropy. If the chemical shift depends upon molecular orientation, as it does in an aromatic ring, then this will also contribute to V t) as a result of motionally induced fluctuations in the electron shielding field. The contribution increases with and typically contributes 0.02 Hz to 1/Ti, in high-field spectrometers. Again, if it arises in partially oriented molecules then it affects lineshape, this time asymmetrically. This is discussed further in chapters 5 and 7. 

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