Shielding parameter

In deuterochloroform, pyrazine shows a single proton resonance at S 8.59 (72CPB2204). Vo, Vm and Vp values between pyrazine ring protons obtained from a number of pyrazine derivatives are 2.5-3, 1.1-1.4 and 0 Hz respectively, and these values do not appear to be affected by the nature of the ring substituents. Some substituent shielding parameters are shown in Table 1. 

Table 1 Substituent Shielding Parameters in Substituted Pyrazines ...

The sensitivity of 13C solid-state chemical shifts to small conformational changes is well illustrated by the case of i-PB. Table 1 summarizes some chemical shifts differences for the forms, which have been interpreted in terms of variations of the y-shielding parameter corrected for the deviations, with respect to the exactly G conformations, in the slightly different nearly gauche — nearly trans sequences, characterizing the three crystalline forms of i-PB [116]. 

This subject has been associated with the development of the or and type scales almost from the start74 (see Section II.B), but the first paper in which sulfinyl and sulfonyl groups played a part appears to have been one by Taft and coworkers in 196367. The main object of this paper was to study the effect of solvent on the inductive order by 19F NMR measurements on a large number of mcta-substituted fluorobenzenes in a great variety of solvents. The relationship between the NMR shielding parameter and selected systems as equation 10 ... 

The effective CF models, intended to include covalence effects via effective charges and shielding parameters [46] (superposition model [47], effective charge model [48], simple overlap model [49, 50]), keep the radial (M-L distance) dependence of the CF parameters as in the simple (point charge) electrostatic model. Dedicated studies have shown, however, that the radial dependence of these parameters deviates strongly from the latter for the whole series of lanthanide ions [51, 52]. 

Fio. 6. Proton-shielding parameters for the binary hydrides of the elements plotted against the atomic number t>f the central atom. Explanation of symbols ... 

Fro. 7. i F Shielding parameters for the binary fluorides plotted against the atomic number of the central atom—molecular species. ( )ai((calc.) (DjaiS) o)ap 8) ( ) CTp(obs.). 

The actual field Hat the nucleus thus will be H() -applied field at the nucleus, it is called the magnetic shielding parameter. The more shielding there is, the stronger the applied field must be to satisfy the resonance condition,... 

The variation of the pressure against the confinement radius is shown in Figure 6. Figure 7 shows the behavior of the ls-2p transition wavelength against different values of the Debye shielding parameter X and the... 

Since there is not much of conjugation between the P=0 group and the nitrogen in (2), 0 and N atoms can in principle behave as two independent basic centers. Medium effects upon the PMR shielding parameters of phosphoramidates demonstrated that in such a strong acid as trifluoromethanesulfonic amides (2) indeed exist, at least partly, as the 0 and N diprotonated species. 

Finally there is a desperate need for greater correlations of these structural and theoretical studies of the nature of the mctal-unsaturated molecule interaction with other experimentally derived quantities. We have in mind correlations with spectroscopically derived quantities, such as stretching frequencies and NMR shielding parameters. But we also have in mind the most important problem of the correlation of the metrical details of the bonding with the reaction chemistry. If the discovery and... 

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