Concerning the internal rotational potential in benzal chloride. 37Cl/35Cl isotope effect on the methine 1H NMR

1989 ◽  
Vol 67 (12) ◽  
pp. 2053-2056 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Phenyl Group ◽  
Lattice Relaxation ◽  
Methine Proton ◽  
Spin Coupling ◽  
Spin Lattice Relaxation ◽  
Spectral Parameters ◽  
Spin Lattice ◽  
H Nmr

1H NMR spectral parameters are reported for benzal chloride in CS2/C6D12, CDCl3, and acetone-d6 solutions. The values of 6J (H,CH), the long-range spin–spin coupling constant between the side-chain and para protons, are consistent with twofold barriers to rotation about the exocyclic C—C bond of 8.6(4), 8.9(4), and 10.2(6) kJ/mol, in the order of the solvents above. These numbers are somewhat smaller than the twofold barrier of 11.6 kJ/mol available from STO-3G MO computations for the free molecule. Alternatively, an internal rotational potential consisting of a twofold term of 17.0 kJ/mol and a fourfold term of −5.5 kJ/mol is also compatible with the 6J (H,CH) measured for the CDCl3 solution and with the 13C spin-lattice relaxation data reported for such a solution. The 6J (H,CH) values demonstrate that the conformer with the a C—H bond situated in the benzene plane is the most stable. A local minimum in the potential for a conformer in which this bond lies in a plane perpendicular to the phenyl group, leading to a population of about 8% for this conformer at 300 K and compatible with the magnitude of 6J (H,CH), is represented by twofold and fourfold terms of 6.0 and 4.5 kJ/mol, respectively. The barrier height is then only 8.0 kJ/mol, however. 37Cl/35Cl isotope effects on the methine proton amount to −0.17, −0.19, and −0.22 parts per billion in CS2, CDCl3, and acetone-d6 solutions, respectively (increased screening). Keywords: benzal chloride, internal potential, 37Cl/35Cl isotope effect on 1H NMR.

Bonded Hydrogen and Trapped H2 in a-Si1−xGex:H Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
E. J. Vanderheiden ◽  
G. A. Williams ◽  
P. C. Taylor ◽  
F. Finger ◽  
W. Fuhs
Keyword(s):  
Temperature Dependence ◽  
Molecular Hydrogen ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Local Environments

ABSTRACT1H NMR has been employed to study the local environments of bonded hydrogen and trapped molecular hydrogen (H2) in a series of a-Si1−xGex:H alloys. There is a monotonic decrease of bonded hydrogen with increasing x from ≈ 10 at. % at x = 0 (a-Si:H) to ≈ 1 at. % at x = 1 (a-Ge:H). The amplitude of the broad 1H NMR line, which is attributed to clustered bonded hydrogen, decreases continuously across the system. The amplitude of the narrow 1H NMR line, which is attributed to bonded hydrogen essentially randomly distributed in the films, decreases as x increases from 0 to ≈ 0.2. From x = 0.2 to x ≈ 0.6 the amplitude of the narrow 1H NMR line is essentially constant, and for x ≥ 0.6 the amplitude decreases once again. The existence of trapped H2 molecules is inferred indirectly by their influence on the temperature dependence of the spin-lattice relaxation times, T1. Through T1, measurements it is determined that the trapped H2 concentration drops precipitously between x = 0.1 and x = 0.2, but is fairly constant for 0.2 ≤ x ≤ 0.6. For a-Si:H (x = 0) the H2 concentration is ≈ 0.1 at. %, while for x ≥ 0.2 the concentration of H2 is ≤ 0.02 at. %.

Nuclear magnetic resonance spin–lattice relaxation and the rotation of adamantane and hexamethylenetetramine in solution

1977 ◽  
Vol 55 (13) ◽  
pp. 2564-2569 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Brian A. Pettitt
Keyword(s):  
Variable Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Hard Sphere Model ◽  
Correlation Times ◽  
Spin Lattice ◽  
H Nmr ◽  
Large Step ◽  
Resonance Spin

Deuterium nmr spin–lattice relaxation times have been measured for dilute solutions of adamantane-d16 in CH2I2, CHBr3, CCl4, CHCl3, and CH2Cl2. The reorientation correlation times, τ2, calculated from the experimental data are used to calculate τJ, the angular momentum correlation times, assuming both the J-diffusion and Hubbard relations. The derived τJ values suggest that adamantane executes small step diffusion in CH2I2 and CHBr3, and large step diffusion in CCl4, CHCl3, and CH2Cl2. The calculated τJ values do not appear to be related to the mean times between collisions calculated using a hard sphere model. Both variable solvent and variable temperature experiments indicate 1 ps/cP for the viscosity dependence of the adamantane reorientation time, about 1/36th the value predicted using the familiar Stokes–Einstein equation.Carbon-13 and 1H nmr T1 data indicate that reorientation of hexamethylenetetramine in H2O (28 ps/cP), CHCl3 (27 ps/cP), and CHBr3 (18 ps/cP) is severely hindered because of inter-molecular hydrogen bonding.

Deuterium NMR Study of the Solid-Solid Phase Transition in Phenethylammonium Bromide

1991 ◽  
Vol 46 (8) ◽  
pp. 691-696 ◽  
Author(s):  
Marco L. H. Gruwel ◽  
Roderick E. Wasylishen
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Line Shape ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
H Nmr ◽  
Line Shapes ◽  
Low Temperature Phase

AbstractUsing 2H NMR, the dynamics of the cation in phenethylammonium bromide were studied in the two solid phases. Line shape and spin-lattice relaxation rate studies of the ammonium headgroups and the adajacent methylene groups indicate the onset of alkyl-chain motion prior to the first order phase transition. In the low-temperature phase the line shape and the spin-lattice relaxation rates of the -ND3 groups are consistent with C3 jumps and an activation energy of 54±4 kJ mol-1. However, in the high-temperature phase the spin-lattice relaxation studies indicate the presence of small-angle diffusion of the -ND3 groups around the C3 symmetry axis. In this phase the -CD2- groups show line shapes typical of large-amplitude two-site jumps occurring at a rate > 107 s-1 . In the low-temperature phase, at temperatures below 295 K, the -CD2- 2H NMR line shapes indicate that the C - D bonds are essentially static

Proton Magnetic Resonance and Molecular Motion in Solid Methyl-Piperidines and Piperazines

1977 ◽  
Vol 32 (8) ◽  
pp. 882-885 ◽  
Author(s):  
R. Schüler ◽  
L. Brücher ◽  
W. Müller-Warmuth
Keyword(s):  
Proton Magnetic Resonance ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Spin Lattice ◽  
H Nmr ◽  
Second Moments ◽  
Line Narrowing

Abstract The 1H-NMR spin-lattice relaxation time and lineshape in solid 2-, 3-, and 4-methyl-piperidine, in 2-and N-methyl-piperazine, and in NN′-diinethyl-piperazine has been measured from low temperatures to the melting point. For all cases, the experimental data can be described by classical rotation of the methyl group. Activation energies governing this motion are between 9 and 14 kJ/mole. Second moments are reduced from about 25 G2 to 17 G2. No further line-narrowing was observed.

Molecular Motions in Halogen-Bridged One-Dimensional Pt Complexes, [PtII(en)2][PtIVX2(en)2](ClO4)4 (X = Cl, Br) Studied by 2H and 1H NMR

2002 ◽  
Vol 57 (6-7) ◽  
pp. 413-418 ◽  
Author(s):  
Noriyoshi Kimura ◽  
Toru Hachisuka ◽  
Yukitaka Nakano ◽  
Ryuichi Ikeda
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Energy Difference ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Potential Wells ◽  
One Dimensional ◽  
X Ray ◽  
Spin Lattice ◽  
H Nmr

2H and 1H NMR measurements were performed on crystalline [Pt(en)2][PtX2(en)2](ClO4)4 (X = Cl, Br), where the protonated and partially deuterated ethylenediamines (en’s), NH2(CH2)2NH2, NH2(CD2)2NH2 and ND2(CH2)2ND2 were used as ligands. Measurements of 2H and 1H NMR spin-lattice relaxation times showed the presence of motions of en chelate rings at the temperatures near the phase transitions, whereas broad 2H NMR spectra and the reported X-ray diffraction data showed no marked motions. These results were consistently explained by introducing the en puckering motion between highly asymmetric potential wells with an energy difference of 10 - 13 kJ mol-1. This difference was shown to be much larger than 2 - 5 kJ mol-1, reported for the iodo-complex, [Pt(en)2][PtI2(en)2](ClO4)4

H NMR Study of Ionic Motions in High Temperature Solid Phases of (CH3NH3)2ZnCl4

2000 ◽  
Vol 55 (3-4) ◽  
pp. 412-414 ◽  
Author(s):  
Hiroyuki Ishida
Keyword(s):  
Activation Energy ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
The Self ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Self Diffusion ◽  
Spin Lattice ◽  
H Nmr ◽  
Nmr Study

Abstract The reorientation of the tetrahedral complex anion ZnCl42- and the self-diffusion of the cation in (CH3NH3)2ZnCl4 were studied by 1H NMR spin-lattice relaxation time (1H T1) experiments. In the second highest-temperature phase, the temperature dependence of 1H T1 observed at 8.5 MHz could be explained by a magnetic dipolar-electric quadrupolar cross relaxation between 1H and chlorine nuclei, and the activation energy of the anion motion was determined to be 105 kJ mol -1 . In the highest-temperature phase, the activation energy of the self-diffusion of the cation was determined to be 58 kJ mol -1 from the temperature and frequency dependence of 1H T1

A study of 14N relaxation and nitrogen–proton spin coupling in Watson–Crick base pair models through Fourier transform measurements on NH proton spin–lattice relaxation in the rotating frame

1979 ◽  
Vol 57 (9) ◽  
pp. 1075-1079 ◽  
Author(s):  
Michael E. Moseley ◽  
Peter Stilbs
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Lattice Relaxation ◽  
Indirect Measurements ◽  
Spin Lattice ◽  
Proton Coupling ◽  
Nuclear Spin Lattice Relaxation

Indirect measurements of nitrogen-14 nuclear spin-lattice relaxation times and direct proton coupling constants are presented together with carbon-13 T1 data for a series of alkyl-substituted nucleic acid bases and mixtures thereof in DMSO-d6. With the exception of the guanine NH nitrogen, which possibly experiences a decrease in the electric field gradient upon complexation with cytosine, no indications of significant changes in the electronic environment around the nitrogen nuclei were found for any combination of bases. Forsen–Hoffman spin saturation transfer experiments on the NH and NH2 protons are also presented.

NQR-NMR and Raman Study of a Structural Phase Transitionin (NH4)2PbCl6

1989 ◽  
Vol 44 (2) ◽  
pp. 109-116 ◽  
Author(s):  
C. Dimitropoulos ◽  
J. Pelzl
Keyword(s):  
Relaxation Rate ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Threefold Axis ◽  
Spin Lattice Relaxation Rate ◽  
Spin Lattice ◽  
H Nmr ◽  
Lattice Relaxation Rate ◽  
Angle Rotation

Abstract The temperature dependence of the chlorine NQR frequency and spin-lattice relaxation rate indicate a structural phase transformation in (NH4)2PbCl6 at 80 K similar to that observed in (NH4)2TeCl6 at 85 K. Both transitions are characterized by a discontinuity of the temperature derivative of the NQR frequency shift and by a cusp in the NQR spin-lattice relaxation rate, but no splitting of the NQR line is observed below Tc. These observations point towards a transition that leaves the chlorine sites equivalent, such as a small angle rotation of the MXg2-6octahedra about their threefold axis. Supplementary 1H-NMR measurements have been performed to investigate the direct influence of NH4+ motion on the Cl-NQR. The phase transitions in mixed (NH4: K)2PbCl6 crystals have also been studied.

Molecular Motion in Azulene and the Azulenes–(s)-Trinitrobenzene Molecular Complex in the Solid State

1973 ◽  
Vol 51 (22) ◽  
pp. 3774-3780 ◽  
Author(s):  
C. A. Fyfe ◽  
G. J. Kupferschmidt
Keyword(s):  
Solid State ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Spectral Parameters ◽  
X Ray ◽  
Spin Lattice ◽  
Wide Line ◽  
Experimental Values

Molecular motion of azulene in its own molecular crystal and in its complex with trinitrobenzene has been shown from wide-line n.m.r. and spin–lattice relaxation time measurements to occur in the solid state. Calculations of the n.m.r. spectral parameters based on a model where the azulene molecules are reorienting in their molecular planes by 180° jumps give satisfactory agreement with experimental values. The results are discussed with respect to the available X-ray data.

NMR Experiments on Molecular Dynamics in Nanoporous Media: Evidence for Lévy Walk Statistics

1996 ◽  
Vol 464 ◽  
Author(s):  
Rainer Kimmich ◽  
Tatiana Zavada ◽  
Siegfried Stapf
Keyword(s):  
Field Gradient ◽  
Lattice Relaxation ◽  
Cauchy Distribution ◽  
Relaxation Dispersion ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Lévy Walk ◽  
Levy Walk ◽  
Nmr Diffusometry

ABSTRACTField-cycling 1H and 2H NMR relaxometry and field-gradient 1H NMR diffusometry were applied to polar and nonpolar liquids filled into porous glasses and fineparticle agglomerates (SiO2, ZnO, TiO2, globular proteins). The orders of magnitude of the length scales of the pore spaces ranged from 100 to several 102 nm. Pronounced differences of the spin-lattice relaxation dispersion for “weak” (nonpolar) and “strong” (polar) adsorption were found. In the latter case, the correlation times of the adsorbate orientation are up to eight orders of magnitude longer than in bulk. Trans-lational diffusion in liquid surface layers was directly studied with the aid of field-gradient NMR diffusometry in systems where the free liquid was frozen. The spin-lattice relaxation dispersion can be explained on the basis of reorientations mediated by translational displacements (RMTD) of adsorbate molecules on the surfaces. Thisprocess appears to be enhanced by a Levy walk mechanism so that the propagator adopts the form of a Cauchy distribution. The evaluated surface correlation functions are characterized by surface correlation lengths in the same order as the pore diameters, that is, up to three orders ofmagnitude larger than the length scale of dipolar interaction.

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