Chemical shift Ramsey equation

A more quantitative attempt at interpreting platinum chemical shifts requires that we consider some form of the Ramsey (48) equation, which describes the resonance frequency, v9 in terms of the paramagnetic screening term, o>- QAB is a charge-density, bond-order matrix, AE is the average excitation energy, and r represents a distance from the nucleus for, in this case, a given d electron. 

In the past fifty years, the NMR Chemical Shielding have evolved from corrections to the measurement of nuclear magnetic moments as quoted from Ramsey s 1950 original papers (Phys. Rev. 77, 567 and 78, 699), to one of the most important tools for structural elucidation in many branches of chemistry. There are no simple relationships between molecular structure and chemical shifts. Their dependence on the molecular electronic and geometrical structure can be derived via complex quantum mechanical equations. 

Octahedral cobalt complexes, CoL, have three filled t2 and two empty e molecular orbitals. The Co chemical shifts of several such complexes are linear with the wavelength of the first absorption (longest wavelength) in the UV/visible spectrum. Explain the linearity in terms of Ramsey s equation for shielding. 

A general theory of chemical shifts of magnetic nuclei has been given by Ramsey, and the screening constant for a particular nucleus has been conveniently expressed in terms of three main contributions by equation (9)—... 

The suitable nonrelativistic starting point for understanding NMR chemical shifts is Ramsey s equation (5) [13]. 

Historically, the first attempts to extend Ramsey s equation to take into account relativistic effects were by perturbation theoretical inclusion of SO contributions [16]. This leads to a third-order perturbation treatment that lends itself very nicely to a detailed interpretation of SO effects on chemical shifts. We will come back to the third-order perturbation theoretical ansatz in section 2.4. Before, we will concentrate on approaches, in which SO coupling is included in the zeroth-order Hamiltonian, in a relativistic four- or two-conponent framework. This is probably the preferred fi amework from a purely theoretical point of view, and it is most appropriate when relativistic effects are large, i.e. for systems containing very heavy atoms. 

There are several books to which one can refer for more detailed technical information but, in general, chemical shifts for heavy and/or quadrupolar nuclei are rationalized on the basis of the Ramsey expression, equation (l) 5- 8 jqj. overall shielding (cr), made up of diamagnetic (oj) and paramagnetic (paramagnetic parameter, reflects the electron density in the immediate... 

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