Quadrupole Resonance Spectrum of Chloranil and Its Hexamethylbenzene Complex
01 Jun 1960-Journal of Chemical Physics (American Institute of Physics)-Vol. 32, Iss: 6, pp 1882-1883
TL;DR: The nuclear quadrupole resonance spectrum of chloranil and in the 1: 1 complex with hexamethylbenzene was obtained at 77 tained K and room temperature.
Abstract: The nuclear quadrupole resonance spectrum of Cl in chloranil and in the 1: 1 complex of chloranil with hexamethylbenzene was obtained at 77 tained K and room temperature. The results are used to estimate the upper limit for charge transfer in the complex from chloranil to hexamethylbenzene. Complexes of picrylchloride: hexamethylbenzene and parachloroaniline: sym-trinitrobenzene were also studied but no resonances were detected. (D. L.C.)
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01 Jan 1972
TL;DR: The crystal field effect is of the order of δv (35Cl) = ±500 kHz in Cl atoms bound to carbon as discussed by the authors, which is equivalent to an increasing antishielding factor γ∞ for Cl.
Abstract: A quantitative investigation of the crystal field effect is quite difficult. From the large number of NQR measurements available, the following qualitative conclusions can be drawn.
a)
The crystal field effect is of the order of δv (35Cl) = ±500 kHz in Cl atoms bound to carbon.
b)
With increasing ionic character of a bond Cl-X, the crystal field effects become more pronounced, because the multipole moments of the molecules in the lattice and the quadrupole polarizability of the core electrons of the 35Cl nucleus increase. This second point is equivalent to an increasing antishielding factor γ∞ for Cl.
c)
Quantitative calculations of the charge transfer in molecular compounds or of the ionic character induced within a molecule through the formation of the complex are only possible if the crystal structure is known and single-crystal NQR data (including η) are available. From NQR powder data, only qualitative conclusions can be drawn.
d)
The temperature dependence of NQR frequencies should be investigated carefully to correct for the crystal field effect as accurately as possible.
e)
For other nuclei besides 35Cl, and 79,81Br, such as 127I, 14N,..., more experimental evidence is needed to clarify the connection between NQR and the specific interactions between molecules in the solid state and in molecular addition compounds.
22 citations
TL;DR: A review of applications which were developed between 1956 and 1961 is presented in this article, where the nuclear quadrupole resonance is used to explore the electronic structure in crystalline solids.
22 citations
17 citations
TL;DR: In this paper, the authors studied nitrogen and chlorine pure quadrupole resonance spectra in some charge transfer complexes with a chloroform molecule as acceptor, the donors being some amino and heterocyclic compounds.
Abstract: We have studied nitrogen and chlorine pure quadrupole resonance spectra in some charge transfer complexes with a chloroform molecule as acceptor, the donors being some amino and heterocyclic compounds. A discussion of the present results and consideration of previous data confirm the charge transfer in these complexes. From the observed frequency shifts with respect to the uncomplexed compounds, the charge transfer can be estimated to a few per cent of an electron charge. Nous avons etudie la resonance quadripolaire pure de l'azote et du chlore dans quelques complexes a transfert de charge. L'accepteur y est le chloroforme, tandis que les donneurs y sont des amines ou des heterocycles. La discussion des resultats obtenus, compte tenu de donnees anterieures, semble confirmer le transfert de charge dans ces complexes. L'estimation du transfert, a partir des deplacements de frequence mesures, fournit une valeur egale a quelques centiemes de la charge electronique.
17 citations
TL;DR: In this paper, the 35Cl NQR frequencies from 11 organic molecules and 3 inorganic molecules were given for 77°K and discussed in terms of σ and π inductive and conjugative effects of groups relative to the chlorine and compared to frequencies in analogous molecules.
Abstract: The 35Cl NQR frequencies from 11 organic molecules and 3 inorganic molecules are given for 77°K. The frequencies are discussed in terms of σ and π inductive and conjugative effects of groups relative to the chlorine and compared to frequencies in analogous molecules. In [PCl4]+[BCl4]−, frequencies from both ions have been detected, and in [SCl3]+[SbCl6]− the first frequencies to date from [SCl3]+ have been measured.
16 citations
References
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TL;DR: In this article, the results of experiments on nuclear quadrupole resonances of antimony and chlorine isotopes in solids were compared with theoretical results for quadrupoles and thermal vibrations, and effects of a nuclear hexadecapole.
Abstract: Experimental measurements on nuclear quadrupole resonances of chlorine and antimony isotopes in solids have been made to an accuracy of about 0.001 percent. The results are compared in detail with theoretical results for (1) nuclear quadrupole interaction, (2) interaction between quadrupole coupling and thermal vibrations, and (3) effects of a nuclear hexadecapole. The ratio $\frac{{(\mathrm{eQq})}_{{\mathrm{Cl}}^{35}}}{{(\mathrm{eQq})}_{{\mathrm{Cl}}^{37}}}$ varies between 1.268736 and 1.268973 while $\frac{{(\mathrm{eQq})}_{{\mathrm{Sb}}^{123}}}{{(\mathrm{eQq})}_{{\mathrm{Sb}}^{121}}}$ varies from 1.274714 to 1.274770. These variations may be attributed to zero-point vibrations and to thermal vibrations, so that no clear evidence is found for nuclear polarization by surrounding electric fields. For $p$-dichlorobenzene, the temperature coefficient of the coupling constant of Cl and the variation of isotopic coupling ratio with temperature are shown to be in fair quantitative agreement with the extension of Bayer's theory of vibrational effects. Relaxation times, Zeeman effects, and certain effects due to crystal structure are examined. Small discrepancies in the measured ratios of frequencies of transitions in ${\mathrm{Sb}}^{121}$ and ${\mathrm{Sb}}^{123}$, which can be attributed to nuclear hexadecapole interactions are found. These indicate a hexadecapole coupling constant in ${\mathrm{Sb}}^{123}$ of 24 kc/sec and a ratio of the ${\mathrm{Sb}}^{123}$ hexadecapole coupling to that of ${\mathrm{Sb}}^{121}$ of 0.8\ifmmode\pm\else\textpm\fi{}0.3. A convenient high-sensitivity circuit for observation of nuclear resonances in solids has been developed and is discussed.
160 citations
TL;DR: In this paper, it was shown that Hammett's σ−values can be correlated with electron densities calculated by the MO LCAO method, which can be used to calculate reasonable values for absorption frequencies, mesomeric moments, and orienting power of the substituents.
Abstract: It is shown that Hammett's σ‐values can be correlated with electron densities calculated by the MO LCAO method. Since Coulomb and exchange integrals for atoms other than carbon are not accurately known, an absolute calculation of σ's is not possible. Nevertheless, σ‐values permit derivation of a self‐consistent and reasonable set of parameters which can be used to calculate reasonable values for absorption frequencies, mesomeric moments, and orienting power of the substituents.
104 citations
TL;DR: A linear correlation exists between the Cl35 pure quadrupole resonance frequency in substituted chlorobenzenes and the Hammett parameter sigma for the substituent as mentioned in this paper.
Abstract: A linear correlation exists between the Cl35 pure quadrupole resonance frequency in substituted chlorobenzenes and the Hammett parameter sigma for the substituent. The relation is expressed as f=1.024σ+34.826 Mcps. For the 52 frequencies used in determining this relation, the correlation coefficient is r = 0.96 and the root‐mean‐square deviation of the experimentally determined f values from those predicted by the equation is 360 kcps.A proper ortho sigma parameter for use in the f vs σ correlation is apparently the value derived from the Hammett relation σ = lnK/K0 in which K and K0 are the equilibrium constants for ionization of the substituted and unsubstituted benzoic acid in water at 25°C. This parameter is linearly proportional to the polar substituent σ* of Taft for the ortho substituent.In the many multiply substituted chlorobenzenes investigated, the proper total sigma value has been taken as the sum of the individual parameters. Few cases are apparent in which the linear relation of f to σ is se...
93 citations
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