Phase transitions and molecular motions in adamantane derivatives: 1-adamantanol

1987 ◽  
Vol 65 (8) ◽  
pp. 1757-1760 ◽  
Author(s):  
Pierre D. Harvey ◽  
Denis F. R. Gilson ◽  
Ian S. Butler
Keyword(s):  
High Temperature ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Adamantane Derivatives ◽  
Hydroxyl Groups ◽  
Temperature Phase ◽  
Spin Lattice

An order–disorder transition occurs in 1-adamantanol at 359 K on heating and at 342 K on cooling, with transition entropies of 36 and 34 J K−1 mol−1, respectively. FT-ir spectra show that free hydroxyl groups exist in the high temperature phase, but the majority of the O—H groups remain hydrogen bonded. The barrier to adamantyl group rotation in the low-temperature phase, determined from proton spin–lattice relaxation time measurements, is 20.9 Kj mol−1, and the barrier to rotation in the high-temperature phase is 35.0 kJ mol−1.

Dynamic Behavior of Group 13 Elements in Bromocomplexes as Studied by NQR and NMR

2000 ◽  
Vol 55 (1-2) ◽  
pp. 117-123 ◽  
Author(s):  
Yasumasa Tomita ◽  
Hiroshi Ohki ◽  
Koji Yamada ◽  
Tsutomu Okuda
Keyword(s):  
Activation Energy ◽  
High Temperature ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Group 13 ◽  
Spin Lattice ◽  
Temperature Dependences

NMR, NQR, powder X-ray diffraction, DTA and AC conductivity were measured in RMBr4 (R = Ag, Cu; M = Al, Ga) and RM2Br7 (R = Li, Ag; M = Al, Ga). In RMBr4 , the activation energy of Cu+ diffusion was evaluated from 63Cu NMR and was in good agreement with that from 81Br NQR. In CuAlBr4 , the e2Qq/h value of 63Cu NMR and the η value of 27AI NMR changed linearly with decreasing temperature, although the e2Qq/h value of 27AI NMR did not change so much. These temperature dependences are supposed to be due to Cu+ diffusion and not to a variation of the lattice constants. In RM2Br7 , the activation energy was obtained from the spin-lattice relaxation time T1 of 81Br NQR and is ascribed to a modulation of the cation diffusion. The line width of 7Li NMR in LiAl2Br7 was about 5.9 kHz in the low-temperature phase and 0.4 kHz for the high-temperature phase. The 27AlNMR spectrum was broadened by the quadrupole interaction and unchanged up to 400 K, suggesting that diffusion of Li+ ions occurs in the high-temperature phase.

Phase transitions in solid cycloheptene

1990 ◽  
Vol 68 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Julian Haines ◽  
D. F. R. Gilson
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Low Temperature Phase

The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.

1H Nmr Study Of Molecular Motions In Thiourea Pyridinium Nitrate Inclusion Compound

2004 ◽  
Vol 59 (7-8) ◽  
pp. 505-509 ◽  
Author(s):  
M. Grottela ◽  
A. Kozak ◽  
A. Pajzderska ◽  
W. Szczepański ◽  
J. Wąsicki
Keyword(s):  
Inclusion Compound ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
Nmr Study ◽  
Pyridinium Cations

The proton NMR second moment and spin-lattice relaxation time have been studied for polycrystalline thiourea pyridinium nitrate inclusion compound and its perdeuderated analogues in a wide temperature range. The reorientation of two dynamically different pyridinium cations around their pseudohexagonal symmetry axis taking place over inequivalent barriers have been revealed in the low-temperature phase. Activation parameters for these motions have been derived. A symmetrization of the potential barriers has been observed at the transition from intermediate to the high temperature phase. The motion of thiourea molecules has been also evidenced, but could not be unambiguously described.

A Proton NMR Study of n-Decylammonium Chain Dynamics in the Perovskite-type Layered Compound (C10H21NH3)2CdCl4

1993 ◽  
Vol 48 (4) ◽  
pp. 563-569 ◽  
Author(s):  
Stefan Jurga ◽  
Kazimierz Jurga ◽  
Eduard C. Reynhardt ◽  
Piotr Katowski
Keyword(s):  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Layered Compound ◽  
Temperature Phase ◽  
Potential Wells ◽  
Spin Lattice ◽  
Compound C ◽  
Nmr Study

Abstract A detailed proton second moment and spin-lattice relaxation time investigation of the bilayered compound (C10H21NH3)2 CdCl4 is reported. In the low temperature phase the methyl group exe-cutes a classical threefold reorientation, while the NH3 group is involved in a similar reorientation in an asymmetric potential well. Evidence for defect chain motions in this phase has been found, and infomation regarding the potential wells associated with these motions has been extracted from the data. In the high temperature phase, slow chain defect motions and fast fourfold reorientations of chains about their long axes, parallel to the normal to the bilayer, have been observed.

Motions of Methylammonium Ions in (CH3NH3)2ZnBr4 Crystals Studied by 1H NMR and Thermal Measurements

1990 ◽  
Vol 45 (7) ◽  
pp. 923-927
Author(s):  
Hiroyuki Ishida ◽  
Kentaro Takagi ◽  
Tadashi Iwachido
Keyword(s):  
Solid Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Self Diffusion ◽  
Spin Lattice ◽  
H Nmr

AbstractMeasurements of the 1H spin-lattice relaxation time T1, the linewidth parameter T*2the second moment of 1H NMR absorption, differential thermal analysis, and differential scanning calorimetry were performed on methylammonium tetrabromozincate(II) crystals from 58 to above 500 K. A solid-solid phase transition was located at 456 K. In the room temperature phase, 120° reorientational jumps of CH3 and NH3+ groups in the cation about its C -N bond axis were detected. In the high-temperature phase, the cations undergo overall reorientation as well as translational self-diffusion. The activation energy for the cationic self-diffusion was evaluated to be 18 kJ mol-1 .

Nuclear magnetic resonance studies of molecular motion in guanidinium chloride, bromide, and iodide

1985 ◽  
Vol 63 (6) ◽  
pp. 1239-1244 ◽  
Author(s):  
Christopher I. Ratcliffe
Keyword(s):  
High Temperature ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Fold Axis ◽  
Guanidinium Chloride ◽  
Spin Lattice ◽  
H Nmr

Guanidinium [Formula: see text] chloride, bromide, and iodide salts have been studied by 1H and 2H nmr as a function of temperature. The 2H powder lineshapes show conclusively that reorientation of the guanidinium ion occurs about the principal three-fold axis in the chloride, bromide, and high temperature phase of the iodide. Activation energies for this process have been obtained from 1H spin-lattice relaxation results. The question of whether or not there are concurrent two-fold flips of the —NH2 units is discussed, but must presently remain unresolved. It was found that the high temperature phase of the iodide can be supercooled.

Proton Spin Lattice Relaxation in the Dimethylammonium Group

1993 ◽  
Vol 48 (5-6) ◽  
pp. 713-719
Author(s):  
K. Venu ◽  
V. S. S. Sastry
Keyword(s):  
Experimental Data ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Dipolar Interactions ◽  
Spin Temperature ◽  
Spin Lattice ◽  
Molecular Group

Abstract A model for the spin lattice relaxation time of the protons of dimethylammonium in the Redfield limit and common spin temperature approximation is developed. The three fold reorientations of the methyl groups, the rotation of the whole molecular group around its two fold symmetric axis and possible correlations among these motions are considered. The effect of these processes on the dipolar interactions among the protons within the same molecular group is taken into account. The resulting relaxation rate is powder averaged and used to explain the experimental data in literature on [NH2(CH3)2]3Sb2Br9 . The analysis shows that dynamically inequivalent groups exist in this compound and that the effect of proposed correlation among the different motions on the final results is negligible.

NUCLEAR MAGNETIC RELAXATION IN GAS MIXTURES

1962 ◽  
Vol 40 (8) ◽  
pp. 1027-1035 ◽  
Author(s):  
D. Llewelyn Williams
Keyword(s):  
Room Temperature ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Gas Molecules ◽  
De Broglie Wavelength ◽  
Diffraction Effects ◽  
Good Agreement

Measurements of the proton spin–lattice relaxation time using pulse techniques have been made on the hydrogen–nitrogen, hydrogen–neon, and hydrogen–helium systems from room temperature to 60° K. The results are in good agreement with the Oppenheim–Bloom theory and illustrate the importance of the radial distribution of the gas molecules and of diffraction effects associated with the de Broglie wavelength.

Surface Induced Spin-Lattice Relaxation of Water in Tricalcium Silicate Gels

1991 ◽  
Vol 46 (8) ◽  
pp. 697-699
Author(s):  
F. Milia ◽  
Y. Bakopoulos ◽  
Lj. Miljkovic
Keyword(s):  
Grain Size ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Tricalcium Silicate ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Water Proton ◽  
Hydration Time ◽  
Spin Lattice ◽  
Stage Process

AbstractThe water proton spin-lattice relaxation time and recovery function of exchangeable water was measured in tricalcium silicate (C3S) gels. The measurements were carried out as a function of the hydration time and grain size. Results show that the hydration of (C3S) is a two stage process. A model is developped

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