Shielding theory

Recent Advances in Nuclear Magnetic Shielding Theory and Computational Methods... 

Gauss has derived shielding theory with electron correlated calculations in the Moller-Plesset expansion (43,44) and also in the coupled cluster approach (45). He has provided benchmark calculations on a set of small molecules shown in Tables II and III at the CCSD(T) level (46). 

The following discussion is divided into three parts. The first part reviews fundamental principles of shielding theory and establishes the basis for the calculations. The second part summarizes the calculations and results pertaining to the main concrete structure, and the final part discusses numerous supplementary shielding problems associated with the design of the reactor structure,... 

R. B. Schulz, V. C. Plantz, D. R. Brush, Shielding Theory and Practice. IEEE Trans Electromag Compat 1988, 30,187-201. 

Jameson, C. J. Recent Advances in Nuclear Magnetic Shielding Theory and Computational Methods , in Modeling NMR Chemical Shifts, Gaining Insights into Structure and Environment (ACS Symposium Series 732) Facelli, J. C., Ed., ACS Washington DC, 1999, pp 1-23. 

R 350 J.C. Facelli, Calculations of Chemical Shieldings. Theory and Applications , Concepts Magn.Reson., A, 2004,20A,42... 

For the theory of neutralization of the magnetic effect on the conductor in a non-magnetic shielding, refer to the continuous enclosures for isolated phase bus systems discussed in Section 31.2.2. As a result of non-magnetic shielding there will be no saturation of the iron core and the V-I characteristic of the reactor will remain almost linear. 

The theory for plane jets is similar to descriptions of circular jets (see Section 7.4) and many derived equations describe both two-dimensional (plane) and three-dimensional (round) jets. The principle is to generate such high air velocity that a shield against pressure difference, temperature difference, and wind velocity is sustained. Howeveg it is not possible to have complete separation by an air curtain. The main reason for this, is that the jet entrains air... 

Other measures of nucleophilicity have been proposed. Brauman et al. studied Sn2 reactions in the gas phase and applied Marcus theory to obtain the intrinsic barriers of identity reactions. These quantities were interpreted as intrinsic nucleo-philicities. Streitwieser has shown that the reactivity of anionic nucleophiles toward methyl iodide in dimethylformamide (DMF) is correlated with the overall heat of reaction in the gas phase he concludes that bond strength and electron affinity are the important factors controlling nucleophilicity. The dominant role of the solvent in controlling nucleophilicity was shown by Parker, who found solvent effects on nucleophilic reactivity of many orders of magnitude. For example, most anions are more nucleophilic in DMF than in methanol by factors as large as 10, because they are less effectively shielded by solvation in the aprotic solvent. Liotta et al. have measured rates of substitution by anionic nucleophiles in acetonitrile solution containing a crown ether, which forms an inclusion complex with the cation (K ) of the nucleophile. These rates correlate with gas phase rates of the same nucleophiles, which, in this crown ether-acetonitrile system, are considered to be naked anions. The solvation of anionic nucleophiles is treated in Section 8.3. 

The theory has been advanced that the rapid growth of marine fouling in the tropics may provide a protective shield which counteracts the effect of the greater activity of the hotter water, and LaQue" has pointed out that in flowing sea water, when no fouling organisms became attached to small fully immersed specimens, corrosion of steel at 11° C proceeded at 0-18 mm/y compared with 0-36 mm/y at 21° C. This increase corresponds with what would be expected from chemical kinetics, where the rate of reaction is approximately doubled for a rise of 10° C. 

Vaara, J., Malkina, O.L., Stoll, H., Malkin, V.G. and Kaupp, M. (2001) Study of relativistic effects on nuclear shieldings using density-functional theory and spin-orbit pseudopotentials. Journal of Chemical Physics, 114, 61-71. 

Malkin, V. G., Malkina, O. L., Salahub, D. R., 1993, Calculations of NMR Shielding Constants by Uncoupled Density Functional Theory , Chem. Phys. Lett., 204, 80. 

Schreckenbach, G., Ziegler, T., 1997a, Calculation of NMR Shielding Tensors Based on Density Functional Theory and a Scalar Relativistic Pauli-Type Hamiltonian. Application to Transition Metal Complexes , Int. J. 

Wiberg, K. B., 1999, Comparison of Density Functional Theory Models Ability to Reproduce Experimental 13C-NMR Shielding Values , J. Comput. Chem., 20, 1299. 

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