Motional behavior of 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose in solution. A 13C spin-lattice relaxation study

1983 ◽  
Vol 61 (7) ◽  
pp. 1542-1548 ◽  
Author(s):  
Photis Dais ◽  
Arthur S. Perlin
Keyword(s):  
Temperature Dependence ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Structural Features ◽  
Spin Lattice Relaxation ◽  
Hindered Rotation ◽  
Spin Lattice ◽  
Resonance Spin ◽  
Diffusional Model ◽  
Motional Behavior

13C nuclear magnetic resonance spin-lattice relaxation times (T1) have been used to probe the motional behavior of 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose (1) in dimethyl sulfoxide solution. This system offers structural features well suited to the study of a variety of internal motions, i.e., ring oscillation, ring puckering interconversion, and methyl internal rotation, all of which are superimposed on an isotropic overall reorientation. Among various models examined to evaluate internal rotations, a two-sites jump model was found satisfactory for interpreting the oscillation and puckering motions of the flexible 5,6-O-isopropylidene ring, whereas a diffusional model described hindered rotation of the geminal methyl groups of the rigid 2,3-O-isopropylidene ring from 15° to 80 °C. The activation energy associated with the temperature dependence of the rate of overall molecular tumbling was found to agree with the hydrodynamical prediction of 4.57 kcal/mol associated with the temperature dependence of the ratio (η/T). In addition, an explicit treatment of the relaxation data vs. solution viscosities, as a function of temperature, indicated that 1 reorients under the "slip" boundary conditions.

Motional behavior of "asperlin" in solution. A 13C spin-lattice relaxation study

1986 ◽  
Vol 64 (3) ◽  
pp. 560-565 ◽  
Author(s):  
Photis Dais ◽  
George Fainos
Keyword(s):  
Lattice Relaxation ◽  
Structural Features ◽  
Spin Lattice Relaxation ◽  
Single Type ◽  
Relaxation Data ◽  
Pyrone Ring ◽  
Spin Lattice ◽  
Internal Motions ◽  
Resonance Spin ◽  
Motional Behavior

l3C nuclear magnetic resonance spin-lattice relaxation times (T1) have been used to probe the motional behavior of 5-acetoxy-5,6-dihydro-6-(1,2-epoxypropyl)-2-pyrone ("asperlin") in dimethyl sulfoxide solution. This molecule offers structural features suited to a study of internal motions, i.e., epoxypropyl and methyl internal motions superimposed on an anisotropic overall reorientation. The rigidity of the pyrone ring and its semiplanar conformation result in an overall ellipsoidal shape, and hence the rotational dynamics of asperlin are adequately approximated by the diffusion of a prolate ellipsoid with the major axis passing through the C(2)—H(2) bond. The description of the internal motion of the epoxypropyl ring is strongly model dependent. Furthermore, the relaxation data for the oxirane ring carbons do not uniquely define a dynamic model. Due to similarities in the activation energies of the overall and internal motions, based on temperature-dependent measurements, it has not been feasible to interpret the relaxation data by a single type of motion. Internal rotation of the epoxymethyl substituent is rationalized by applying the stochastic diffusion model of multiple internal rotations

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.

A proton magnetic resonance relaxation study of molecular motions in trimethylamine-borane

1976 ◽  
Vol 54 (7) ◽  
pp. 1087-1091 ◽  
Author(s):  
T. T. Ang ◽  
B. A. Dunell
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Solid Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Free Induction ◽  
Resonance Spin ◽  
Resonance Relaxation

Proton magnetic resonance spin–lattice relaxation times T1 have been measured for trimethylamine-borane from 120 to 380 K, a few degrees above the melting point. Minima in T1 at 157 and 259 K are attributed to threefold reorientation of each of the three methyl groups and the borane group and to threefold reorientation of the whole molecule about the B—N axis, respectively. Activation energies for these processes were found to be 3.3 and 6.7 kcal/mol. Abrupt changes in T1 at 350 and 360 K correspond exactly with heat capacity transitions observed by other workers. The time constant for the decay of the free induction signal (FID curve) changes by two orders of magnitude at 360 K. Having a value of some 3 ms above 360 K, it shows that there must be rapid diffusion as well as molecular tumbling in the highest temperature solid phase.

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