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.

A Pulsed Proton Magnetic Resonance Study of Some Organic Compounds

1984 ◽  
Vol 39 (6) ◽  
pp. 548-552 ◽  
Author(s):  
Fevzi Köksal ◽  
Semiha Bahçeli
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Spin Diffusion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Tertiary Butyl ◽  
Methyl Group ◽  
Spin Lattice ◽  
Relaxation Parameters

Spin-lattice relaxation times (T1) of protons in polycrystalline dimethyl sulfone, stearic acid, stearyl alcohol, trimethylamine-N-oxide, tertiary-butylhydrazine hydrochloride and tertiary-butyl carbamate have been measured over a range of temperatures by pulsed proton magnetic resonance. Except for tertiary-butyl carbamate a single minimum in T1 was observed for all the compounds. The T1 results have been interpreted by considering the methyl group reorientations about the C3 axis and the role of the spin diffusion of the other protons to the methyl protons in the compounds. The double minima in T1 for tertiary-butyl carbamate have been attributed to reorientations of methyl groups in the tertiary-butyl group about the C3′ axis and reorientations of each methyl group about its C3 axis. The spin-lattice relaxation parameters have been determined.

Proton Magnetic Resonance in Natural Rubber: Comparison with Dielectric Measurements

1964 ◽  
Vol 37 (1) ◽  
pp. 268-284
Author(s):  
Hazime Kusumoto ◽  
H. S. Gutowsky
Keyword(s):  
Magnetic Resonance ◽  
Natural Rubber ◽  
Line Width ◽  
Sulfur Content ◽  
Proton Magnetic Resonance ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Spin Lattice

Abstract Proton magnetic resonance studies have been made of cured natural rubber containing up to 31 per cent combined sulfur. Line shapes and spin-lattice relaxation times were observed at temperatures between −190° and 180° C. In the line shape studies, the main effect of the combined sulfur was upon the temperature at which the line width is narrowed by the molecular segmental motions. The temperature at the onset of the major line width narrowing increases from −50° C for raw rubber to about 10° C for 31 per cent combined sulfur. A relation was found between the dependence upon sulfur content of the line width changes and the second-order transition temperature. The proton spin-lattice relaxation time T1 was measured for three cured samples in the temperature range above the motional narrowing region. The T1 vs. temperature curves agree qualitatively with the theory of Kubo and Tomita. The general features of the T1 curves are consistent with a distribution of correlation times which broadens with increasing sulfur content. Energies of activation were computed from these results and they are compared with the dielectric relaxation data obtained previously. The effect of a distribution of correlation time is discussed.

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