Shielding correlation

From an extensive set of data concerning annelation of cyclopropane rings to cyclopentanes, Christl and coworkers were able to employ y-syn shielding and y-anti shielding correlations to assign structures. Four compounds which contain all four valencies within one hemisphere, inverted carbons , were considered these were 41, 24, 42, 43 and their respective precursors without the cyclopropyl methylene group viz 44, 45, 11, 46. 

For compounds with substituted pyridine ligands, increased shielding correlates well with increasingly negative values for the ring-substituent... 

Electromagnetic interference (EMI) testing has become more prevalent for materials that either emit or are affected by EMI. Shielding efficiency (SE) of materials is deterrnined by measuring electric field strength between a transmitter and receiver with or without the presence of the material under test. Several researchers have suggested a correlation between volume resistivity and SE values (300,301). 

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. 

Plot para chemical shift (vertical axis) vs. para atomic charge (horizontal axis). Are the two properties correlated If they are, what is their relationship Does chemical shift increase ( C becomes deshielded) or decrease ( C becomes shielded) with increasing negative charge at carbon ... 

Correlations in nuclear magnetic shielding, part I. J. Mason, Adv. Inorg. Chem. Radiochem., 1976, 18,197-228 (99). 

The correlation analysis of spectroscopic properties in terms of a,- and crR-type parameters has been very important. Substituent effects on 19F NMR shielding in... 

A. Haas and U. Niemann Correlations in Nuclear Magnetic Shielding. Part 1 Joan Mason... 

Schreckenbach, G., 1999, The 57Fe NMR Shielding in Ferrocene Revisited. A Density-Functional Study of Orbital Energies, Shielding Mechanisms, and the Influence of the Exchange-Correlation Functional , J. Chem. Phys., 110, 11936. 

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