Nuclear quadrupole resonance frequencies

The reduction of the C— Br and C—1 group moments from 1.10 and 0.90 in bromo- and iodo-benzene to about 0.80 and 0.50 in 2-bromo- and 2-iodo-thiophene has been ascribed to the larger weight of resonance forms such as (8) and (9) in the thiophene series. The chlorine, nuclear, quadrupole, resonance frequencies of chloro-substituted thiophenes are much higher than those of the corresponding benzene derivatives. This has been ascribed to a relayed inductive effect originating in the polarity of the C—S o-bond in thiophenes. The refractive indices, densities, and surface tension of thiophene, alkyl- and halo-thiophenes, and of some other derivatives have been... 

The electronic structure of dichorodiphenylplumbane was calculated by the SCF-MS (self-consistent field multiple scattering) molecular orbital method and compared to that of dichlorodiphenylstannane. The results suggest that one has to look for 35C1 NQR (nuclear quadrupole resonance) frequencies of dichorodiphenylplumbane in the 5-6 MHz region1613. 

Fig. 13. Molecular (a) and possible electronic (b) structure of l2Clg. The table (c) shows the nuclear quadrupole resonance frequencies and derived data...

The carbon-halogen bond distances in acyl halides increase in the direction F < Cl < Br < I, and are similar, but slightly larger than, those of the alkyl halides (Table 7). Nuclear quadrupole resonance frequencies of halogen compounds suggest that the charge density on the chlorine atom of an acyl chloride is greater than that on an alkyl chloride (Table 8). 

Cl NUCLEAR QUADRUPOLE RESONANCE FREQUENCIES OF HALOGEN COMPOUNDS... 

The extraordinarily big shift of the nuclear quadrupole resonance frequency in the etherate of trichlorogermane in comparison with trichlorogermane itself (9 MHz from 23 to 14 MHz) can also be explained by a change in the coordination of the central atom to the trigonal-pyramidal form20. 

An unambiguous success of the n-a overlap model of the anomeric effect is its ability to rationalise 35C1 nuclear quadrupole resonance frequencies in axial and equatorial glycopyranosyl chlorides (David, 1979). The axial chlorides invariably resonate at lower frequency, in accord with the more ionic nature of the C—Cl bond and hence the more spherically symmetrical distribution of electrons around the chlorine nucleus. 

Grechishkin V.S., Yusupov M.Z. The nature of shifts of nuclear quadrupole resonance frequency in Menshutkin complexes // Zh. strukt. khimii. - 1973. -N14. - P. 1028-1032. 

By convention nuclear quadrupole coupling constants are quoted as the quantity e2Qqzjh and expressed in frequency units, usually MHz. It must be noted that nuclear quadrupole resonance frequencies cannot be used to determine the sign of the coupling constant and that only its magnitude can be determined. 

Table 2. Chlorine nuclear quadrupole resonance frequencies of the PtClS complex ion with a variety of monovalent cations...

Table 4. Halogen nuclear quadrupole resonance frequencies of some nontransition metal complexes of the type A MX at room temperature...

I. P. Biryukov, M. G. Voronkov and I. A. Safin, Tables of Nuclear Quadrupole Resonance Frequencies , Israel Program for Scientific Translation, Jersalem, 1969, Includes frequencies measured at different temperatures (commonly 77 K, 195 K, and 273 K or 298 K) temperature effects in NQR are quite substantial and have not been reviewed here. 

At X-band microwave frequency traditionally employed in ESEEM studies, the envelope modulation patterns are in certain cases not well developed. This applies particularly for weakly coupled nuclei. The intensity of the forbidden transitions are then suppressed and consequently also the modulation depth. The use of a lower microwave frequency than X-band is accordingly expected to be particularly useful for enhancement of the ESEEM for weakly coupled nuclei. Dramatic enhancement of the ESEEM depth was observed for weakly coupled nuclei in initial studies with a pulsed EPR spectrometer constructed to operate at S-band. Nuclear quadrupole resonance frequencies were observed for N in some nitroaromatic systems under cancellation conditions for the hfc, i.e. when V2A - vn 0 in terms of the direct field model [44]. 

The width of the F NMR line in solid NF3 has been measured as a function of temperature from 4.2 K up to the triple point at 66.37 K. These measurements, together with the temperature dependence of nuclear quadrupole resonance frequencies, were analyzed in terms of hindered rotations [11], see also p. 201. 

The chlorine, nuclear, quadrupole, resonance frequencies of chloro-substituted thiophenes are much higher than those of the corresponding benzene derivatives. This has been ascribed to a relayed inductive effect originating in the polarity of the C—S a-bond in thiophenes. ... 

The N-nuclear quadrupole resonance frequencies of pyridine and 4-picoline have been discussed in terms of the atomic orbital electron densities of the nitrogen atom. ... 

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