Activation Energies for Fluxional Behavior in Aryl(pentachlorocyclopentadienyl)mercurials, η1 -C5Cl5 HgR, from 35Cl NQR Relaxation Times

1990 ◽  
Vol 45 (3-4) ◽  
pp. 503-510 ◽  
Author(s):  
Norbert Weiden ◽  
Alarich Weiss ◽  
Gary Wulfsberg ◽  
William Ilsley ◽  
William Ilsley ◽  
...  
Keyword(s):  
Nmr Spectra ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
C Nmr ◽  
Phenyl Mercury

Abstract Solid-state activation energies for fluxional behavior in three aryl-subsituted (pentachlorocyclo-pentadienyl)phenylmercury compounds RHgC5 Cl5 : (pentachlorocyclopentadienyl)(pentamethyl-phenyl)mercury (I, R = C6 (CH3)5 , Eact = 19.3 kJ mol-1); (pentachlorocyclopentadienyl)(2,4,6-tris-(terf-butyl)phenyl)mercury (II, R = 2,4,6-C 6 H 2 (C(CH3)3)3 , Eact = 59.5 kJ mol-1); and (pentachloro-cyclopentadienyl)(phenyl)mercury (III, R = C6H5 , E act = 62.8 kJ mol-1) have beeb obtained from 35Cl NQR spin-lattice relaxation-time measurements. II has also been shown to be fluxional in solution by 13C NMR spectra. II was prepared by an exchange reaction between Hg(C5Cl5)2 and Hg(2,4,6-C6H2(C(CH3)3)3)2 , which reacted readily despite the great steric hindrance present in the latter reagent.

35Cl NQR and Molecular Motion in Solid C6X5Cl (X = H, F)

1992 ◽  
Vol 47 (1-2) ◽  
pp. 330-332 ◽  
Author(s):  
A. D. Gordeev ◽  
G. B. Soifer ◽  
A. P. Zhukov
Keyword(s):  
Relaxation Time ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Melting Points ◽  
Spin Lattice Relaxation Time ◽  
Spin Lattice ◽  
35Cl Nqr

AbstractThe 35Cl NQR frequency and spin-lattice relaxation time of solid chlorobenzene and chloropentafluorobenzene at temperatures from 77 K to the melting points have been measured and explained by thermoactivated librations and reorientations of the molecules around the normal to their plane. The activation energies of these motions have been estimated

Reorientational Motion of Trihalogenomethyl Groups in Organic Compounds as Studied by 35Cl NQR and 19F NMR Spectroscopy

1992 ◽  
Vol 47 (1-2) ◽  
pp. 265-273 ◽  
Author(s):  
Silvia Wigand ◽  
Tetsuo Asaji ◽  
Daiyu Nakamurac
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Reorientational Motion ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Temperature Dependences ◽  
Derivatives Of ◽  
Rotational Interaction

AbstractTrihalogenomethyl derivatives of 4-chloroacetanilide, 4-ClC6H4NHCOCCl3,4-ClC6H4NHCOCF2Cl, and 4 - ClC6H4NHCOCF3 were prepared. The 35Cl NQR and 79FNMR spin-lattice relaxation times T1Q and T1F, respectively, of these compounds were measured at various temperatures. On heating, T1Q of the CCl3 and CF2Cl groups decreased rapidly above ca. 110 and 150 K, respectively, showing the onset of reorientation of the trihalogenomethyl group about the pseudo-triad axis. The activation energies were determined to be 27 and 13 k J mol-1 for the CCl3 and CF2Cl reorientation, respectively. The temperature dependences of the 19F NMR T1F of the CF2Cl and CF3 groups lead to activation energies of 13 and 4.3 kJ mol-1 , respectively, for the same reorientations. T1F of the CF3 group observed above ca. 200 K was attributed to the spin-rotational interaction. The T1Q-1 of ring-chlorine in 4 - ClC 6H4NHCOCCl3 and 4 - ClC6H4NHCOCF3 can be interpreted by the Tn law with n = 2.2 and 1.1, respectively, whereas that of 4-ClC6H4NHCOCF2Cl by the sum of two contributions: Tn law (n = 2.0) and the modulation mechanism due to the CF2Cl reorientation

scholarly journals The Motion of the OH Group in p-Chlorophenol and its Influence on the 35Cl NQR Parameters

1986 ◽  
Vol 41 (1-2) ◽  
pp. 408-411 ◽  
Author(s):  
Mariano J. Zuriaga ◽  
Carlos A. Martin
Keyword(s):  
Activation Energy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Frequency Difference ◽  
Spin Lattice Relaxation ◽  
Normal Behaviour ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Two Temperature ◽  
Nqr Parameters

The 35Cl NQR transition frequencies and the spin-lattice relaxation times, T1, for both lines in p-chlorophenol have been measured in the temperature range 90 - 310 K. The frequency difference and the temperature derivatives for both lines clearly show the existence of two temperature intervals with distinct lattice contributions to the EFG. Similarly, T1, data show a normal behaviour due to spin-phonon interactions up to 240 K. Above this temperature T1 begins to shorten in an exponential manner. The hindered motions of the OH group are proposed as responsibles of these effects, and an activation energy of 26 kJ mol-1 is determined.

35Cl NQR Studies of Bismuth Trichloride

1997 ◽  
Vol 52 (8-9) ◽  
pp. 614-620
Author(s):  
P. K. Babu ◽  
J. Ramakrishna
Keyword(s):  
Temperature Dependence ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Positive Temperature Coefficient ◽  
Spin Lattice Relaxation ◽  
Positive Temperature ◽  
Lattice Vibrations ◽  
Spin Lattice ◽  
Quadrupole Resonance ◽  
35Cl Nqr

Abstract The temperature dependence of the 35Cl nuclear quadrupole resonance (NQR) frequency and spin lattice relaxation time (T1) are studied in crystalline BiCl3 , in the range 40-300 K. The positive temperature coefficient observed for one of the 35Cl resonances is explained in terms of the strong intermolecular interactions that exist in this compound. Variation of with temperature is found to be similar at the chemically inequivalent halogen sites. Semiclassical descriptions based on torsional oscillator dynamics are found to be inadequate for explaining the spin lattice relaxation. T1 (T) data follow an AT2 + BT3 type behaviour, indicating that the anharmonic nature of the lattice vibrations plays a significant role in determining the temperature dependence of T1 at high temperatures.

Hydrogen Isotope Effect on the Temperature Dependence of the 35Cl-NQR Frequency in (NH4)2IrCl6

2002 ◽  
Vol 57 (6-7) ◽  
pp. 504-508 ◽  
Author(s):  
Yoshio Kume ◽  
Tetsuo Asaji
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Ammonium Ion ◽  
Energy Separation ◽  
Rotational States ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Deuterated Analogue ◽  
Hydrogen Isotope Effect

The 35Cl-NQRfrequencies and spin-lattice relaxation times of (NH4)2IrCl6 and (ND4)2IrCl6 were measured in the temperature range 4.2 - 300 K. It was confirmed that no phase transition takes place down to 4.2 K. The observed frequency at 4.2 K in (ND4)2IrCl6 was higher by 18 kHz than that in the non-deuterated analogue. This discrepancy was attributed to a difference between the lowest rotational states of the ammonium ions in these compounds. The energy separation between the ground state and excited state of rotational motion, in which N-H of the ammonium ion rotates among the three directions slightly apart from the triad axis, was estimated by fitting analysis to be 31 cm-1 and 93 cm-1 for (ND4)2IrCl6 and (NH4)2IrCl6, respectively. The activation energy of the reorientation of the ammonium ion among the four directions of the triad axis was estimated to be 6.9 and 7.6 kJ mol-1, respectively

A 35CL NQR Spin-Lattice Relaxation Study on the Motion of D4h Anions in [C(NH2)3]2PdCl4, [C(NH2)3]2PtCl4, and [C(NH2)3]AuCl4

1986 ◽  
Vol 41 (1-2) ◽  
pp. 416-420
Author(s):  
Yoshihiro Furukawa ◽  
Daiyu Nakamura
Keyword(s):  
Relaxation Times ◽  
Sharp Decrease ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Dependent ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
The One ◽  
Increasing Temperature ◽  
Complex Anions

The temperature dependence of 35Cl NQR spin-lattice relaxation times T1ClQ was observed for the crystal of the title complexes. For the Pd(II) and Pt(II) complexes, the log T1ClQ vs. 103 T-1 curves having gentle positive gradients at lower temperatures decreased sharply with increasing temperature from ca. 150 and ca. 130 K, respectively. This sharp decrease of T1ClQ can be explained by the C4 reorientation of the D4h complex anions with the activation energy Ea of 34 kJ mol-1 for the former and 29 kJ mol-1 for the latter complex. These values agree well with those estimated from 1H T1 showing temperature dependent dipolar-quadrupolar cross relaxation. For the Au(III) salt, two of four 35Cl NQR lines showed a sharp decrease in T1ClQ from ca. 270 K, suggesting the onset of the C4 reorientation of the one kind crystallographically equivalent anions with Ea of 67 kJ mol-1.

Conformation of ring A in triterpenoid ketones. Carbon-13 chemical shifts and spin-lattice relaxation times of lupane and 18α-oleanane derivatives

1989 ◽  
Vol 54 (7) ◽  
pp. 1928-1939 ◽  
Author(s):  
Miloš Buděšínský ◽  
Jiří Klinot
Keyword(s):  
Chemical Shifts ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Chair Conformation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Structural Assignment ◽  
Boat Form ◽  
The One ◽  
C Nmr

13C NMR spectra of sixteen lupane and 19β,28-epoxy-18α-oleanane triterpenoids I-XVI were measured and a complete structural assignment of chemical shifts was made. For most compounds also the carbon spin-lattice relaxation times T1 were obtained. Characteristic differences in chemical shifts of some carbon atom signals were found between 2α-methyl-3-oxo and 2α-methyl-1-oxo derivatives II, V and VIII with chair conformation of the ring A on the one hand and their 2β-isomers III, VI and IX (boat form) on the other. Using these 2-methyl ketones as models, the chair-boat population in allobetulone (I), 3-oxo-28-lupanenitrile (IV) and 1-oxo derivative VII was determined. The results agree well with the data obtained by other physical methods.

scholarly journals Possibilities of proton magnetic resonance in determination the cellulose crystallinity

2019 ◽  
Vol 59 (8) ◽  
pp. 116-123
Author(s):  
Yury B. Grunin ◽  
◽  
Maria S. Ivanova ◽  
Keyword(s):  
Relaxation Time ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Active Surface ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Cellulose Crystallinity ◽  
Spin Lattice ◽  
Free Induction

A layered model of the structural organization of macrofibrils of native cellulose, consisting of microfibrils, which include elementary fibrils, has been developed. A feature of the proposed model is the presence of slit-like pores between the crystalline elements of cellulose. It was found that, on average, each water molecule interacts with one glucose residue of the surface chains of cellulose with the formation of hydrogen bonds in the framework of monolayer adsorption. This allows to establish a correlation between the cellulose crystallinity and the capacity of the adsorption water monolayer on its active surface. Based on the condition of rapid molecular exchange between the adsorption water layers in the framework of the Bloembergen-Purcell-Pound theory, an approach is proposed for determination the capacity of water monolayer. The obtained values are consistent with the results of solving the Brunauer-Emmett-Teller equation for the adsorption isotherm of water on the active surface of cellulose. The Fourier transform of the free induction decay signal of cellulose allows to estimate its crystallinity at various moisture contents. Methods have been developed for assessing the crystallinity of different types of dry cellulose based on NMR relaxation parameters — spin-lattice relaxation time and spin-spin relaxation time. Using the method of deuteration of cellulose, the relaxation times of its crystalline regions were determined. The results of preliminary studies showed that the crystallinity of cotton cellulose is higher in comparison with the same parameter of woody types of cellulose. A comparison of the literature and the data we obtained using 1H-NMR relaxation confirmed the possibility of utilizing the developed methods to solve the tasks of scientific research and conducting quality control of cellulosic materials at specialized enterprises.

Sign in / Sign up

Export Citation Format

Share Document