Experimental Shielding Effectiveness

Experimentally, shielding effectiveness is measured using instrument called network analyzer (NA). Both scalar NA (SNA, which record only the magnitude of the incident, reflected, and transmitted signals) and vector NA (VNA, which also measures the associated phases) are used for shielding measurements [1,3]. Particularly, the VNA signals carry information about attenuation constant as well as dielectric/magnetic properties. 

Therefore, from the knowledge of reflected and transmitted signals, i.e., R and T, VNA can easily compute SE and SE components of SE., . 

---

The acid-base properties of 4-nitroso-5-aminopyrazoles 50 have been studied. In particular, protonation sites have been determined where salts 51 are formed [66], The effects produced on II, 13C, and 15N chemical shifts by protonation and by hydrogen-bonding solvents on five azoles (imidazole, 4,5-dimethylimidazole, pyra-zole, 3,5-dimethyl-pyrazole, and 4,5-dihydro-3-methyl-2//-benz[g]indazole) have been determined experimentally. Phase effects on the 13C chemical shifts of the C-4 atom of pyrazole were discussed, based both on empirical models and on GIAO calculations of absolute shieldings in different complexes. The special case of the chemical shifts of pyrazoles in the solid state, where they form multiple N-H N hydrogen bonds, was also studied theoretically [88],... 

The most significant contribution to the overall screening constant is due to the diamagnetic term, which arises from the electrons in the filled shells surrounding the nucleus. It depends on the electronic ground state of the molecule and has a shielding effect. The variations in chemical shift can be ascribed mainly to variations in the paramagnetic term. This has been demonstrated experimentally for 33S in 3- and 4-substituted benzenesulpho-nates.33... 

A small, but resolvable splitting of the resonance line for the tris-chelate complexes of iron(II) is observed (235, 261). In the case of Fe(II)(bipy)3Cl2 AEq (0.34 mm sec ) has been shown to be independent of temperature (29S°-145°K) to within experimental error, although for the series Fe(II)(phen)gX2 AEq was shown to vary slightly with the anion X (207). The small quadrupole splitting presumably reflects the symmetry of the cations (261). Epstein (235) has compared the spectra of Fe(bipy) +, Fe(phen) +, and Fe(phen-R) + where R = 5-nitro, 5-chloro, 5,6-dimethyl, or 3,4,7,8-tetramethyl. Since in such a closely related series the d-electron shielding effects should be similar, it was considered that the isomer shift (8) should be a measure of covalent bond strength. The... 

---