Showing papers on "Nuclear quadrupole resonance published in 1972"
TL;DR: The 14N nuclear quadrupole resonance spectra and spin-lattice relaxation times of the amino acids histidine, methionine, cystine, Cysteine and tyrosine as well as of the nucleic bases uracil, thymine, cytosine, and guanine have been determined by a 14N-proton double resonance technique in the laboratory frame as mentioned in this paper.
Abstract: The 14N nuclear quadrupole resonance spectra and spin‐lattice relaxation times of the amino acids histidine, methionine, cystine, cysteine, and tyrosine as well as of the nucleic bases uracil, thymine, cytosine, and guanine have been determined by a 14N‐proton double resonance technique in the laboratory frame. The experiments were performed on polycrystalline samples at 77°K or above this temperature. A theoretical estimate of the sensitivity of this method for a variety of experimental conditions is as well presented. It is shown that in contrast to usual double resonance techniques the method works even in the case of a short proton spin‐lattice relaxation time if only the nitrogen relaxation time is long.
68 citations
TL;DR: In this paper, a sensitive nuclear double resonance method enables measurement of naturally abundant 17 O nuclear quadrupole resonance transition frequencies in powdered organic compounds, enabling the identification of resonances from C�O, CO-C groups in a set of compounds.
53 citations
TL;DR: In an attempt to study interactions between the π system and the substituents, pure quadrupole resonance of Cl · C6H4 · CCl3 was studied of its Zeeman effect (77 K), the temperature dependence of the three resonance lines (20 −279 K, mp), and the relaxation times T1, T2 and T 2 ∗ (77 −278 K) as discussed by the authors.
30 citations
TL;DR: In this paper, three nuclear quadrupole resonance lines were observed in chloral hydrate at temperatures 20-300K, the frequencies being 38.2863±0.0004 MHz(ν1), 39.5415± 0.0002(ν2), and 39.6252± 0.0002(π).
Abstract: Three nuclear quadrupole resonance lines were observed in chloral hydrate at temperatures 20–300K, the frequencies being 38.2863±0.0004 MHz(ν1), 39.5415±0.0002(ν2), and 39.6252±0.0002(ν3) at 20.3K. Their temperature dependence was measured below 77K, showing monotonous decrease with increasing temperature. The difference in frequency between ν1 and ν2(or ν3) is probably due to a crystal field effect rather than OH···Cl hydrogen bonding as has been suggested. The spin-lattice relaxation time for all the lines, determined by pulse techniques, coincides with each other and tends to decrease rapidly above 250K. The decrease was interpreted as arising from hindered internal rotation of the CCl3 group with the activation energy of 8.8 kcal mol−1.
28 citations
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: In this article, a double nuclear resonance technique was employed to calculate the electric field gradient and the anisotropy constant for five distinct nitrogen sites in the series and the results obtained are shown to be consistent with molecular orbital calculations on these compounds.
21 citations
TL;DR: In this article, the 14N nuclear quadrupole resonance spectra at 77°K of several hydrazines are reported and analyzed in the framework of a semi-empirical theory extended to cover cases of large asymmetry parameters.
Abstract: The 14N nuclear quadrupole resonance spectra at 77°K of several hydrazines are reported and analyzed in the framework of a semiempirical theory extended to cover cases of large asymmetry parameters. The atomic‐orbital occupation numbers obtained by this analysis are linked with the hydrogen‐bonding configuration in the solid state. The results obtained indicate that the hydrogen bonding ability of the amino nitrogen exceeds that of the substituted nitrogen atom and decreases in the order: hydrazine>alkyl hydrazines>N‐amino heterocycles>aryl hydrazines.
19 citations
TL;DR: In this paper, the enhanced proton-nitrogen spin spin spin coupling was utilized to match unequivocally the v+ and v− spectral lines for each nitrogen−14 site for each site, and a relative scale for H, CH3, NH2, NH3+, and OH is obtained.
Abstract: Nitrogen‐14 nuclear quadrupole resonance spectra have been obtained from several substituted ammonium ions. The data are interpreted in terms of the electronegativity of the substituents, and a relative scale for H, CH3, NH2, NH3+, and OH is obtained. The enhanced proton‐nitrogen spin‐spin coupling was utilized to match unequivocally the v+ and v− spectral lines for each nitrogen‐14 site.
16 citations
TL;DR: X-ray diffraction and halogen nuclear quadrupole resonance (n.q.r.) methods were used in this paper to show that Rb3ZnBr5, (NH4)3 ZnCl5, and CsZnI5 have the tetragonal Cs3CoCl5 structure, and ZnI2,2NH3 is isomorphous with corresponding chloride and bromide diammines.
Abstract: X-ray diffraction and halogen nuclear quadrupole resonance (n.q.r.) methods show that Rb3ZnBr5, (NH4)3ZnBr5, and CsZnI5 are isostructural with orthorhombic (NH4)3ZnCl5, and that Rb3ZnCl5 has the tetragonal Cs3CoCl5 structure. ZnI2,2NH3 is isomorphous with the corresponding chloride and bromide diammines. Rb2ZnBr4 and (NH4)2ZnBr4 have structures of Cs2ZnBr4 type, although the rubidium salt shows some stacking faults. In the complex chlorides 35Cl n.q.r. frequencies are grouped about 9 MHz, while the bromides have 81Br frequencies grouped around 60 MHz. The ½ → 3/2 transitions of 127I in the iodides are in the region of 76 MHz. The diammine compounds ZnBr2,2NH3 and ZnI2,2NH3 have frequencies close to the mean values for the ZnBr42- and ZnI42- ions respectively, but in the hydrates ZnCl2,l⅓H2O,ZnBr2,2H2O, β-KZnBr3,2H2O, and KZnI3,2H2O the halogen frequencies are increased. N.q.r. and X-ray data are also reported for the compound Cs3CuCl5, formed by quenching the melt. This compound slowly disproportionates at room temperature into Cs2CuCl4 and CsCl.
16 citations
TL;DR: In this article, the 14N chemical shifts of some monosubstituted pyridines are reported and the shifts may be satisfactorily explained in terms of the average excitation energy approximation if both π- and σ-bond polarization is considered by means of SCF-MO calculations and 14N nuclear quadrupole resonance data.
Abstract: The 14N chemical shifts of some monosubstituted pyridines are reported. They show a correlation with the electronic nature of the substituent which is not found with earlier 14N chemical shift data. The shifts may be satisfactorily explained in terms of the average excitation energy approximation if both π- and σ-bond polarization is considered by means of SCF-MO calculations and 14N nuclear quadrupole resonance data. The 14N N.M.R. line widths are discussed from the point of view of molecular reorientation processes in the liquid state.
14 citations
TL;DR: The 35Cl n.q.r. spectra of cyclodiphosphazanes, (Cl3PNR)2(R = Me, Et, or Ph), are reported in this paper, where axial and equatorial chlorine atoms in the trigonal bipyramidal distribution of atoms about phosphorus in the latter class of compound can be identified by their frequency ranges, and by relative changes in frequency with temperature.
Abstract: The 35Cl n.q.r. spectra of a series of chlorocyclophosphazenes have been obtained and are discussed in the light of their known crystal structures. An approximately linear relationship exists between 35Cl n.q.r. frequencies and P–Cl bond lengths in closely related structures. The 35Cl n.q.r. spectra of the cyclodiphosphazanes, (Cl3PNR)2(R = Me, Et, or Ph), are reported. The axial and equatorial chlorine atoms in the trigonal bipyramidal distribution of atoms about phosphorus in the latter class of compound can be identified by their frequency ranges, and by relative changes in frequency with temperature.
TL;DR: The nuclear quadrupole resonance spectrum of hydrogen-bonded hexamethylenetetramine triphenol was observed at 77°K and at room temperature in this paper.
Abstract: The nuclear quadrupole resonance spectrum of hydrogen bonded hexamethylenetetramine triphenol was observed at 77°K and at room temperature. The absorption lines were assigned to two inequivalent nitrogen sites. N(1), which is not hydrogen bonded, gave e2qQ/h=4665.7 kHz and η=0 at 77°K. N(2), which takes part in an N···H–O hydrogen bond, has e2qQ/h=4208.1 kHz and η=0.05014 also at 77°K. By comparing these data with the spectrum of pure hexamethylenetetramine (HMT) the effects of the hydrogen bond on the HMT nitrogen sites could be obtained. It is concluded that the nitrogen site N(2) loses a few hundredths of an electron from its lone pair orbital as a result of the hydrogen bond interaction.
TL;DR: In this article, the nitrogen quadrupole resonance (NQR) frequencies of nitrogen-containing organic molecules were found to correlate with the enhancement in the superconducting critical temperature caused by intercalating these molecules in layered tantalum disulfide (2HTaS 2 ).
TL;DR: In this paper, a solid-state study of tervalent hexachloro-complexes R3MCl6(M= Rh or Ir) and quadrivalent Hexachlorocomplexes R2MCl 6(M = Mn, Tc, Ru, and Rh) has been carried out by use of X-ray, n.q.r., and i.r. techniques.
Abstract: A solid-state study of tervalent hexachloro-complexes R3MCl6(M= Rh or Ir) and quadrivalent hexachlorocomplexes R2MCl6(M= Mn, Tc, Ru, and Rh) has been carried out by use of X-ray, n.q.r., and i.r. techniques. The 35Cl n.q.r. spectra of the complexes K3RhCl6,H2O, K3lrCl6,H2O, K3lrCl6, and (NH4)3lrCl6,H2O are complex and suggest a low site-symmetry for the anion. This is verified from the low-frequency i.r. spectra of the compounds and a full single-crystal X-ray analysis of K3RhCl6,H2O. The latter complex is orthorhombic and has space-group Pbcn with 8 molecules Z= 8 in a unit cell of dimensions a= 1·2368(9), b= 1·5655(6), and c= 1·2041 (10) nm. The structure was solved from diffractometer data and refined R 0·07 for 920 independent reflexions. The octahedral RhCl63– anions contain six crystallographically independent Rh–Cl bonds ranging in length from 230·2(4) to 236·6(4) pm. The lack of symmetry in the anion appears to be influenced by the neighbouring molecule of water of crystallisation. The n.q.r. spectra of the cubic octahedral quadrivalent complexes R2MCl6(M= Mn, Tc, Ru, or Rh) have been measured and display the same trends as observed previously for the metal hexachloro-complexes of the third transition-series.
TL;DR: In this paper, the existence of a new β form of As 4 S 4 with higher symmetry than the α form was confirmed using nuclear quadrupole resonance and far infrared spectroscopy.
TL;DR: In this article, the nuclear quadrupole resonance frequencies of 75As in the α and β forms of As4S3 have been measured at 77, 195, and 293 K. The frequencies at 77 K were: α phase 64.87 65.94 79.56 MHz β phase 65.42 67.16 79.65 MHz
Abstract: The nuclear quadrupole resonance frequencies of 75As in the α and β forms of As4S3 have been measured at 77, 195, and 293 K. The frequencies at 77 K were: α phase 64.87 65.94 79.56 MHz β phase 65.42 67.16 79.65 MHz An analysis is presented in terms of Townes-Dailey theory and of the temperature dependence in terms of Bayer-Brown theory. The differences in frequencies of the α and β forms were attributed to the effect of electrostatic field gradients, estimated by lattice sums. Allowance must be made for the thermal expansion of the lattice to obtain a consistent interpretation.
TL;DR: In this article, phase equilibria studies and nuclear quadrupole resonance spectroscopy data were used to characterize I3+AlCl4, I5+AlCL4, and I2Cl+Alcl4.
Abstract: Compounds formulated as I3+AlCl4–, I5+AlCl4–, and I2Cl+AlCl4– have been prepared and so characterized according to phase equilibria studies and nuclear quadrupole resonance spectroscopy data.
TL;DR: In this article, an analysis of the data obtained from these investigations suggests the existence of intramolecular O→In coordination in the α-nitroalkyl derivatives of indium.
TL;DR: In this paper, the bromine nuclear quadrupole resonance (NQR) and its Zeeman effect have been observed in the molecular complex of aluminum tribromide with benzene at room temperature.
Abstract: The bromine nuclear quadrupole resonance (NQR) and its Zeeman effect have been observed in the molecular complex of aluminum tribromide with benzene at room temperature. The resonance frequencies are 79.99, 90.10, and 91.18 MHz for 81Br at 301°K. The asymmetry parameters of the field gradient are 28.9±1.1, 8.6±1.0, and 6.0±0.9% for the bromine atoms in the order of increasing resonance frequency. Aluminum tribromide forms the dimer in the complex crystal as well as in the pure state. The bond angle between a pair of terminal bromine atoms and the interbond angle at the bridging bromine atom are found to be 117.3±0.5° and 95.5±0.2° respectively; these values correspond to those of 122±2° and 87±2° obtained from the X-ray analysis. Furthermore, the charge-transfer from the benzene ring to the bromine atom is discussed on the basis of the NQR parameters.
TL;DR: In this paper, the temperature dependence of the nuclear quadrupole resonance (NQR) frequencies and spin-lattice relaxation times for the 35Cl nuclei in Cs2PtCl6, Rb2PteCl6 and K2PdCl6 were measured.
Abstract: Measurements of the temperature dependence of the nuclear quadrupole resonance (NQR) frequencies and spin–lattice relaxation times for the 35Cl nuclei in Cs2PtCl6, Rb2PtCl6, K2PtCl6, and K2PdCl6 pr...
TL;DR: In this paper, the magnitude of the coupling constant, the asymmetry parameter and the orientation of the principal axes of the electric field gradient tensor at the site of a quadrupole nucleus with half integral spin were determined.
Abstract: A new method is proposed for determining the magnitude of the coupling constant, the asymmetry parameter and the orientation of the principal axes of the electric field gradient tensor at the site of a quadrupole nucleus with half integral spin. A function is constructed from the first order splitting of the nuclear quadrupole resonance absorption line produced by a small magnetic field. The parameters of the EFGT are determined from the behaviour of this function for rotation of the crystal around certain axes. A goniometer has been constructed for effecting these rotations and measurement have been made on a single crystal of Ba(ClO 3 ) 2 , H 2 O at the site of chlorine nuclei. It has been found that the chlorines in the unit lattice can be grouped in two sets with two different EFGT having the same value of e q Q =58.6873±.0001 MHz and η=0.027±.007 but different orientations of the principal axes.
TL;DR: In this paper, a generalization of the usual treatment of temperature dependence, which considers the effect on the transition frequencies of molecular oscillations about the principal field gradient axes, is generalized by considering oscillations on an arbitrarily oriented axis system.
Abstract: Nitrogen‐14 nuclear quadrupole resonance (NQR) transition frequencies of the NH2 group of the hydrazinium ion in lithium hydrazinium sulfate have been measured as a function of temperature from 4.2 to 360°K. The usual treatment of temperature dependence, which considers the effect on the transition frequencies of molecular oscillations about the principal field gradient axes, is generalized by considering oscillations about an arbitrarily oriented axis system. This generalization leads to the determination of the orientation of the field gradient axes in the NH2 group, and to a clarification of the existing model of the dynamics of the hydrazinium ion. It is found that between 40 and 320°K the NH2 group undergoes small oscillations about the N–N axis whose amplitude increases linearly with temperature. Above 320°K the amplitude of these oscillations increases more rapidly than a linear function. It is also found that above 150°K, proton exchange in the H–N–H plane of the NH2 group takes place rather than ...
TL;DR: In this article, the authors used NQR tracer measurements on a number of simple reinforced polymers and adhesive bonds and found that the intensity of the tracer signal was in substantial agreement with the reduction expected from the tracers dilution.
Abstract: Nuclear quadrupole resonance (NQR) on dilute inert fillers in several polymers and adhesives is made as a function of compression and tension. The change in the NQR response is found to be proportional to the strain that is applied to the host material. The intensity of the NQR tracer signal is found to be in substantial agreement with the reduction expected from the tracer dilution. The results of NQR tracer measurements on a number of simple reinforced polymers and adhesive bonds are reported.
TL;DR: In this article, the existence of a new type of quadrupole interaction for cubic-symmetry imperfections was established, which is simply a consequence of the ground-vibronic-state degeneracy.
Abstract: The observation and interpretation of weak EPR transitions, identified as 'forbidden' transitions, establish the existence of a new type of quadrupole interaction for cubic-symmetry imperfections. This interaction is simply a consequence of the ground-vibronic-state degeneracy. The signs as well as the magnitudes of the quadrupole-coupling coefficients are determined experimentally. These data agree well with the predictions of crystal field theory modified to account for a weak-to-moderate vibronic interaction (i.e., a dynamic Jahn-Teller effect).
TL;DR: In this paper, Br79 NQR frequencies of a number of bromothiophene derivatives have been measured at 77°K and the frequencies correlate with Hammett δ values.
Abstract: Br79 NQR frequencies of a number of bromothiophene derivatives have been measured at 77°K. The frequencies correlate with Hammett δ values and this correlation demonstrates the importance of the inductive effect. The influences of more than one substituent on the thiophene ring are additive.
TL;DR: The nuclear quadrupole resonance spectrum of the addition complex of antimony pentachloride and cyanogen chloride was recorded in the region of 121 Sb, 123 Sb and 35 Cl transitions.