Secondary correlation

NMR observes the chemistry of only the proton nucleus (though it can observe many other nuclei independently). This means that hetero and metallic chemistry cannot be observed directly. Thus, sulfur, nitrogen, oxygen, and metals cannot be directly analyzed by NMR, though secondary correlations can be obtained from the proton chemistry of the sample. In combination with electron spin resonance (ESR) analyzers that can operate in the fringe fields of the NMR magnet the presence of paramagnetic metals and free radicals can be quantified. 

A number of the Et values for the less polar solvents in Table 10 were not determined from the spectrum of 47, but were based on secondary correlations with ,(30). These are not included in the correlation. 

As the various geometrical parameters are strongly interrelated, additional secondary correlations of other geometrical parameters with the chemical shift emerge. S is apparently correlated with the added lengths of the four... 

Tjandra N and Bax A 1997 Large variations in C-13(alpha) chemical shift anisotropy in proteins correlate with secondary structured. Am. Chem. Soc. 119 9576-7... 

Inhibition of Nitrosamine Formation. Nitrites can react with secondary amines and A/-substituted amides under the acidic conditions of the stomach to form /V-nitrosamines and A/-nitrosamides. These compounds are collectively called N-nitroso compounds. There is strong circumstantial evidence that in vivo A/-nitroso compounds production contributes to the etiology of cancer of the stomach (135,136), esophagus (136,137), and nasopharynx (136,138). Ascorbic acid consumption is negatively correlated with the incidence of these cancers, due to ascorbic acid inhibition of in vivo A/-nitroso compound formation (139). The concentration of A/-nitroso compounds formed in the stomach depends on the nitrate and nitrite intake. 

Application of NMR spectroscopy to heterocyclic chemistry has developed very rapidly during the past 15 years, and the technique is now used almost as routinely as H NMR spectroscopy. There are four main areas of application of interest to the heterocyclic chemist (i) elucidation of structure, where the method can be particularly valuable for complex natural products such as alkaloids and carbohydrate antibiotics (ii) stereochemical studies, especially conformational analysis of saturated heterocyclic systems (iii) the correlation of various theoretical aspects of structure and electronic distribution with chemical shifts, coupling constants and other NMR derived parameters and (iv) the unravelling of biosynthetic pathways to natural products, where, in contrast to related studies with " C-labelled precursors, stepwise degradation of the secondary metabolite is usually unnecessary. 

For steam turbines the cost should be correlated vs. horsepower w ith steam inlet and outlet pressure as secondary variables. 

There is an excellent correlation between these data and the gas-phase data, in terms both of the stability order and the energy differences between carbocations. A plot of the gas-phase hydride affinity versus the ionization enthalpy gives a line of slope 1.63 with a correlation coefficient of 0.973. This result is in agreement with the expectation that the gas-phase stability would be somewhat more sensitive to structure than the solution-phase stability. The energy gap between tertiary and secondary ions is about 17kcal/mol in the gas phase and about 9.5 kcal/mole in the SO2CIF solution. 

Evidence for secondary nucleation has came from the early continuous MSMPR studies. MSMPR crystallization kinetics are usually correlated with supersaturation using empirical expressions of the form... 

A common interpretation of the interaction of chalcogens with nucleophiles considers donation of electron density from a lone pair on the donor atom into the o- (E-X) orbital (Figure 15.1). As the degree of covalency increases, a hypervalent three-centre four-electron bond is formed. Real systems fall somewhere between secondary interactions and hypervalent (three centre - four electron) bonds. The two extremes can be distinguished by the correlation of X-E and E D distances.In the hypervalent case both bond distances decrease simultaneously, whereas in the secondary bond the distances are anticorrelated. This concept has been applied in a study of selenoquinones 15.17 (R = Ph, Me) with short Se 0 contacts,for... 

Z values are obtained from Eq. (8-76) for solvents having Z in the approximate range 63-86. In more polar solvents the CT band is obscured by the pyridinium ion ring absorption, and in nonpolar solvents l-ethyl-4-carbomethoxy-pyridinium iodide is insoluble. By using the more soluble pyridine-1-oxide as a secondary standard and obtaining an empirical equation between Z and the transition energy for pyridine-1-oxide, it is possible to measure the Z values of nonpolar solvents. The value for water must be estimated indirectly from correlations with other quantities. Table 8-15 gives Z values for numerous solvents. 

Hjertberg and coworkers [38-41] were able to correlate the amount of labile chlorine, tertiary and internal allylic chlorine, to the dehydrochlorination rate. They studied PVC samples with increased contents of labile chlorine, which were obtained by polymerization at reduced monomer concentration. According to their results, tertiary chlorine was the most important defect in PVC. In agreement with other reports [42,43], the results also indicated that secondary chlorine was unstable at the temperatures in question, i.e., random initiation would also occur. 

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