Preliminary Results of a 20 K X-Ray Study of Citrinin

1993 ◽  
Vol 48 (1-2) ◽  
pp. 99-104 ◽  
Author(s):  
R. Destro ◽  
F. Merati
Keyword(s):  
Dipole Moment ◽  
Hydrogen Bonds ◽  
Charge Density ◽  
Topological Analysis ◽  
Coupling Constants ◽  
Molecular Dipole ◽  
X Ray ◽  
A Value ◽  
Quadrupole Coupling ◽  
Asymmetry Parameters

Abstract A total of about 37 000 diffracted intensities has been measured at 20 K for a spherical single crystal of citrinin. Using a multipole formalism to interpret the X-ray data, maps of the charge density and of its Laplacian, as well as for the electrostatic potential have been derived. A value of 7(2) D has been obtained for the magnitude of the molecular dipole moment. A study of the electric field gradient (EFG) at the nuclei has yielded the atomic quadrupole coupling constants (QCC) and asymmetry parameters (η). A topological analysis of the charge density has been performed to characterize the intramolecular covalent and hydrogen bonds.

High Pressure NQR Study of the Phase Transition in Anilinium Iodide

1986 ◽  
Vol 41 (1-2) ◽  
pp. 290-293
Author(s):  
Mariusz Maćkowiak ◽  
Maria Zdanowska-Fra̧zek ◽  
Piotr Kozioł ◽  
Jan Stankowski ◽  
Alarich Weiss
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Transition Temperature ◽  
Hydrogen Bonds ◽  
Transition Point ◽  
Pressure Coefficient ◽  
Coupling Constants ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole ◽  
Asymmetry Parameters

The 127I NQR frequency in anilinium iodide C6H5NH3⊕I⊖ was studied at pressures up to 300 MPa and within the temperature range 77 K - 290 K. With increasing pressure the order-disorder transition point Tc is shifted to higher temperatures. The pressure coefficient of the phase transition temperature amounts to dTc/dp = 4.2 x 10-2 deg MPa-1. The pressure coefficient of the NQR frequency is negative. In addition, the 12'I nuclear quadrupole coupling constants and the respective asymmetry parameters η were evaluated as a function of pressure. The results confirm the close connection between the mechanism of the phase transition and the dynamics of the N - H⊕ ...I⊖ hydrogen bonds.

NUCLEAR MAGNETIC RESONANCE SPECTRUM OF B11 IN KERNITE

1955 ◽  
Vol 33 (5) ◽  
pp. 156-175 ◽  
Author(s):  
H. H. Waterman ◽  
G. M. Volkoff
Keyword(s):  
Magnetic Field ◽  
Coupling Constants ◽  
Monoclinic Crystal ◽  
X Ray ◽  
Principal Axes ◽  
Quadrupole Coupling ◽  
Radio Frequency Spectrum ◽  
Asymmetry Parameters ◽  
Crystallographic Axes ◽  
The Magnetic Field

The radio-frequency spectrum of B11 in a single crystal of Na2B4O7∙4H2O (kernite) is examined experimentally as the monoclinic crystal is rotated in an external magnetic field of 7060 gauss in turn about each of three axes (b, c crystallographic axes, and a third perpendicular direction) held normal to the magnetic field. A maximum of 21 lines (some of which show small additional splitting) is observed, which reduces to 11 when the b symmetry axis is perpendicular or parallel to the magnetic field. The results are interpreted in terms of four essentially non-equivalent B11 sites in kernite characterized respectively by quadrupole coupling constants [Formula: see text], 0.588 ± 0.003, 2.563 ± 0.007, 2.567 ± 0.010 Mc./sec, and asymmetry parameters 77 [Formula: see text], 0.60 ± 0.02, 0.163 ± 0.010, 0.116 ± 0.010. The orientations of the principal axes of the four [Formula: see text] tensors are also determined. These observations on boron are consistent with previous X-ray results, but preliminary observations on Na23 in kernite contradict previous X-ray position assignments.

scholarly journals Crystal Structure Refinement and Single Crystal 81Br Zeeman NQR Study of KHgBr3· H2O

1996 ◽  
Vol 51 (12) ◽  
pp. 1197-1202 ◽  
Author(s):  
Hiromitu Terao ◽  
Tsutomu Okuda ◽  
Sachiyo Uyama ◽  
Hisao Negita ◽  
Shi-qi Dou ◽  
...  
Keyword(s):  
Single Crystal ◽  
Room Temperature ◽  
Structure Refinement ◽  
Zeeman Effect ◽  
Coupling Constants ◽  
X Ray ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole ◽  
Asymmetry Parameters ◽  
Good Agreement

Abstract Three 81Br NQR resonance lines of KHgBr3 ·H2O were detected between 77 K and room temperature. From the Zeeman effect measurement on a single crystal the nuclear quadrupole coupling constants (e2qQ/h) and the asymmetry parameters (ƞ) were obtained, which are 228.42 MHz and 0.005, 226.24 MHz and 0.005, and 108.76 MHz and 0.465 for e2qQ/h and ƞ at 295 K, respectively. Large deviations of the observed directions of electric field gradient tensors from the directions expected from previous X-ray results have been found. With the present X-ray redetermination, 81Br NQR and structure are in good agreement. The structure and bonding in the compound are discussed.

The C—CI Bonds in α -2,4,6-tris(trichIoromethyl)-1,3,5-trioxane, α -Parachloral, (Cl3CCHO)3. A 35Cl-NQR Single Crystal Study

1985 ◽  
Vol 40 (4) ◽  
pp. 324-334 ◽  
Author(s):  
Masao Hashimoto ◽  
Norbert Weiden ◽  
Alarich Weiss
Keyword(s):  
Single Crystal ◽  
Coupling Constants ◽  
X Ray Diffraction ◽  
X Ray ◽  
Principal Axes ◽  
Quadrupole Coupling ◽  
35Cl Nqr ◽  
Single Crystal Study ◽  
Nuclear Quadrupole ◽  
Asymmetry Parameters

By single crystal 35C1-NQR Zeeman spectroscopy, the five independent 35Cl nuclear quadrupole coupling tensors in a-parachloral, (Cl3CCHO)3, have been studied at 24 ± 2 °C. The directions of the electric field gradient (EFG) tensor components have been determined. The principal axes Φ are within ± 0.8° parallel to the C-Cl bond directions found by X-ray diffraction. Very small asymmetry parameters in the range 0.002 ≦ η ≦ 0.046 are characteristic for the EFG tensors of chlorine atoms bound to carbon atoms in aliphatic systems. The five nuclear quadrupole coupling constants are in the range 76.752 ≦ e2qQh-1/MRz ≦ 78.155. The orientation of the principal axes Φxx and Φyy can be correlated to the molecular structure.

Hinderungspotential der internen Rotation, Dipolmoment und Quadrupolkopplungskonstanten aus dem Mikrowellenspektrum des 4-Methyl-Pyridins

1967 ◽  
Vol 22 (11) ◽  
pp. 1738-1743 ◽  
Author(s):  
H. D. Rudolph ◽  
H. Dreizler ◽  
H. Seiler
Keyword(s):  
Dipole Moment ◽  
Internal Rotation ◽  
Potential Barrier ◽  
Coupling Constants ◽  
Rotational Spectrum ◽  
A Value ◽  
Microwave Rotational Spectrum ◽  
Quadrupole Coupling ◽  
Substituted Toluenes ◽  
Nuclear Quadrupole

The microwave rotational spectrum of 4-methyl-pyridine (γ-picoline) has been investigated in the region from 8 to 37 GHz. The three types of lines to be expected for a molecule of this symmetry and with a very low sixfold barrier hindering internal rotation of the methyl top have been found: m=0; | m | ≠0, ≠ 3 n; | m |=3 n. From low-/ lines m=0 (a-type transitions) the rotational constants A′ (less methyl top) =6 082.145, B=2 524.850, C=1 783.991 MHz, the dipole moment μα=2.70 D, and the nuclear quadrupole coupling constants for the 14N nucleus χaa= —4.82, χbb—χcc= —2.8 MHz have been determined. From the wide splitting of the lines | m | = 3, | K | = 1 the potential barrier has been derived as V6=13.51 cal/mole, a value which is very close to those previously deduced for toluene and para-substituted toluenes.

Microwave spectrum, dipole moment and quadrupole coupling constants of 1,2,5-selenadiazole

1967 ◽  
Vol 1 (9) ◽  
pp. 379-381 ◽  
Author(s):  
G.L. Blackman ◽  
R.D. Brown ◽  
F.R. Burden ◽  
J.E. Kent
Keyword(s):  
Dipole Moment ◽  
Microwave Spectrum ◽  
Coupling Constants ◽  
Quadrupole Coupling

Thermal-induced transformation of glutamic acid to pyroglutamic acid and self-cocrystallization: a charge–density analysis

2022 ◽  
Vol 78 (2) ◽  
Author(s):  
Sehrish Akram ◽  
Arshad Mehmood ◽  
Sajida Noureen ◽  
Maqsood Ahmed
Keyword(s):  
Hydrogen Bonds ◽  
Glutamic Acid ◽  
Single Crystal ◽  
Diffraction Data ◽  
Density Functional ◽  
Quantitative Estimation ◽  
Topological Analysis ◽  
Pyroglutamic Acid ◽  
X Ray Diffraction ◽  
X Ray

Thermal-induced transformation of glutamic acid to pyroglutamic acid is well known. However, confusion remains over the exact temperature at which this happens. Moreover, no diffraction data are available to support the transition. In this article, we make a systematic investigation involving thermal analysis, hot-stage microscopy and single-crystal X-ray diffraction to study a one-pot thermal transition of glutamic acid to pyroglutamic acid and subsequent self-cocrystallization between the product (hydrated pyroglutamic acid) and the unreacted precursor (glutamic acid). The melt upon cooling gave a robust cocrystal, namely, glutamic acid–pyroglutamic acid–water (1/1/1), C5H7NO3·C5H9NO4·H2O, whose structure has been elucidated from single-crystal X-ray diffraction data collected at room temperature. A three-dimensional network of strong hydrogen bonds has been found. A Hirshfeld surface analysis was carried out to make a quantitative estimation of the intermolecular interactions. In order to gain insight into the strength and stability of the cocrystal, the transferability principle was utilized to make a topological analysis and to study the electron-density-derived properties. The transferred model has been found to be superior to the classical independent atom model (IAM). The experimental results have been compared with results from a multipolar refinement carried out using theoretical structure factors generated from density functional theory (DFT) calculations. Very strong classical hydrogen bonds drive the cocrystallization and lend stability to the resulting cocrystal. Important conclusions have been drawn about this transition.

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