Diamagnetic shielding term

The diamagnetic shielding term nearest neighbor atoms , that is, the ones bonded directly to A. 

According to Equation 124 the diamagnetic shielding terms for the C atoms differ only in the expression Zr IRr q for the monosubstituted allenes, where R denotes the atom of the substituent R which is bonded to Cr. Then, one can introduce reduced substituent constants (125) which give only the paramagnetic shielding contribution to the C / resonance that is, for the allenes we have... 

This transformation thus provides a simple and robust expression for the diamagnetic shielding term, but it has some drawbacks. It makes gauge transformations more complicated we now have... 

The paramagnetic term, apara, derives from the excitation of p-elec-trons by the external held, and its impact is opposite to that of diamagnetic shielding. The term,, derives from the effect of neighboring groups, which can increase or decrease the held at the nucleus, a can also be affected by intermolecular effects, in most cases deriving from interaction of the solvent. 

Here, is a positive term resulting from diamagnetic shielding by electrons localized on atom A, Op is a term (usually negative) which corrects for any deviation from spherical symmetry of the electrons localized on atom A, represents the effect on atom A (shielding or deshielding) of circulation of electrons localized on other atoms, and 0 ° represents the effect on atom A (shield-... 

The term o is called the diamagnetic shielding constant. It is independent of the applied magnetic field and affected by the electron density around the nucleus and the... 

To a good approximation, three terms dominate the C-NMR chemical shifts diamagnetic, paramagnetic, and anisotropy shielding terms [57]. Lamb developed a theoretical expression for the diamagnetic term that focuses on the electron density at a specific nucleus [58]. Therefore, one would expect the carbon s hybridization to have a large chemical shift effect. Obviously, electron deficiency in a carbocation will profoundly effect the chemical shift [59-62]. 

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