Measurement of methyl barriers to rotation from carbon-13 spin-rotation relaxation times

1975 ◽  
Vol 97 (20) ◽  
pp. 5685-5688 ◽  
Author(s):  
A. P. Zens ◽  
Paul D. Ellis
Keyword(s):  
Relaxation Times ◽  
Spin Rotation

Relaxation Processes in the N-Methyl Group of 1,2,2,6,6-Pentamethylpiperidine

1990 ◽  
Vol 43 (2) ◽  
pp. 447 ◽  
Author(s):  
ID Rae ◽  
ML Woolcock
Keyword(s):  
Relaxation Times ◽  
Spin Rotation ◽  
Relaxation Processes ◽  
Methyl Group ◽  
Methyl Methyl ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Relaxation times (T1) and methyl-methyl nuclear Overhauser effects were measured for 1H, 13C and 2H nuclei in 1,2,2,6,6-pentamethylpiperidine and its N-CHD2 analogue which was synthesized by LiAlD4 reduction of the N-CHO compound. The relaxation pathways for hydrogens of the N-CH3 group were estimated to be as follows: spin-rotation 0.046 s-1, dipole-dipole within N-methyl 0.069 s-1, and dipole-dipole with the hydrogens of the C- methyls 0.027 s-1. The 1H{1H) Overhauser effect at the N-CH3 was 7.6%.

103Rh-NMR bei 9,4 T - Verbesserter Nachweis infolge verkürzter Relaxationszeiten und selektivem Polarisationstransfer / 103Rh NMR at 9.4 T - Improved Signal Detection due to Shortened Relaxation Times and Selective Polarisation Transfer

1985 ◽  
Vol 40 (12) ◽  
pp. 1763-1765 ◽  
Author(s):  
Reinhard Benn ◽  
Herbert Brenneke ◽  
Rolf-Dieter Reinhardt
Keyword(s):  
Chemical Shift ◽  
Magnetic Fields ◽  
Signal Detection ◽  
Chemical Shift Anisotropy ◽  
Relaxation Times ◽  
Spin Rotation ◽  
Proton Spin ◽  
High Magnetic Fields

Abstract At 9.4 T the I03Rh relaxation times (T ,) of unsym metrical organorhodium com pounds of the type LR h(7r-ligand) 2 are in the order of seconds, and relaxation is dominated by the Chemical Shift Anisotropy mechanism. In symmetrical complexes like (acac)3Rh (7), T, of 103Rh is considerably longer and dominated by the Spin Rotation mechanism. Through this effect, together with selective polarisation transfer via the Rh olefin-proton spin-spin couplings at high magnetic fields, a significantly improved detection of the insensitive Rh nucleus results

Selenium-77 and phosphorus-31 nuclear spin relaxation in tri-(tert-butyl) phosphine selenide

1991 ◽  
Vol 69 (7) ◽  
pp. 1054-1056 ◽  
Author(s):  
Glenn H. Penner
Keyword(s):  
Chemical Shift ◽  
Nuclear Spin ◽  
Chemical Shift Anisotropy ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Phosphine Selenide ◽  
High Fields

Selenium-77 and phosphorus-31 spin-lattice relaxation times are reported for tri-tert-butylphosphine selenide in chloroform-d, at 303 K and at several different magnetic field strengths. At moderate fields the 31P–1H dipole–dipole, spin-rotation, and chemical shift anisotropy mechanisms contribute significantly towards the 31P T1. At high fields chemical shift anisotropy dominates. The selenium-77 nuclear spin relaxes almost exclusively by spin rotation at low to moderate fields and the chemical shift anisotropy contribution only becomes significant at very high fields. This is due to an unusually small 77Se CSA. The contribution due to 31P–77Se dipole–dipole interactions is small but significant. Key words: 77Se NMR, NMR relaxation, phosphine selenide.

A Nuclear Spin Relaxation Study of the Spin–Rotation Interaction in Symmetric Top Molecules

1972 ◽  
Vol 50 (12) ◽  
pp. 1262-1272 ◽  
Author(s):  
Robin L. Armstrong ◽  
James A. Courtney
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Effective Spin ◽  
Spin Lattice ◽  
Simple Exponential Function ◽  
Symmetric Top Molecules

The spin–lattice relaxation times T1 of 1H, 19F, and 31P nuclei were measured in gaseous samples of BF3, CHF3, CH3F, PH3, and NH3 at room temperature for densities from 0.03 to 10 amagat. In several cases the behavior of T1 at the lowest densities snowed deviations from the linear variation characteristic of the extreme narrowing region. The spin–rotation interaction provides the dominant relaxation mechanism in all cases. The data are analyzed on the basis of the assumption that the collision modulated spin–rotation interaction may be described by a single correlation function which is a simple exponential function of time. Values of an effective spin–rotation constant and a cross section for molecular reorientation are obtained for each gas. The results obtained are compared with those available from other types of experiments. This comparison indicates that the theory for spin–lattice relaxation in dilute gases of symmetric top molecules needs to be carefully reassessed.

Spin-rotation relaxation times at different temperatures for methyl compounds with hindrance barriers

1978 ◽  
Vol 32 (2) ◽  
pp. 227-231 ◽  
Author(s):  
A Tancredo ◽  
P.S Pizani ◽  
C Mendonca ◽  
H.A Farach ◽  
C.P Poole ◽  
...  
Keyword(s):  
Relaxation Times ◽  
Spin Rotation ◽  
Different Temperatures

Spin-rotation relaxation times for methyl compounds with hindrance barriers at 65°C

1980 ◽  
Vol 70 (1) ◽  
pp. 112-113 ◽  
Author(s):  
P.S. Pizani ◽  
A. Tancredo ◽  
C. Mendonca ◽  
H.A. Farach ◽  
C.P. Poole ◽  
...  
Keyword(s):  
Relaxation Times ◽  
Spin Rotation

13C and 2H spin–lattice relaxation in neopentane-d12

1978 ◽  
Vol 56 (19) ◽  
pp. 2576-2581 ◽  
Author(s):  
Brian A. Pettitt ◽  
Roderick E. Wasylishen ◽  
Ronald Y. Donc ◽  
T. Phil Pitner
Keyword(s):  
Melting Point ◽  
Variable Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Rotation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Single Temperature ◽  
Momentum Correlation

The results of a variable temperature study of the 2H and 13C spin–lattice relaxation times in neopentane-d12 are reported. along with those for the 13C's in neopentane at a single temperature. Orientational and angular momentum correlation times derived from these T1's exhibit the following: (i) τ2 is continuous through the melting point with an activation energy of 0.98 kcal/mol, (ii) τJ is more or less constant at 0.33 ± 0.03 ps within 40 K of either side of the melting point, and (iii) they do not conform to the theoretical relationships of extended diffusion, Fokker–Planck, or Langevin theories. The spin–rotation coupling constants are calculated to be −0.69 kHz for neopentane and −0.52 kHz for neopentane-d12

Étude par relaxation nucléaire du proton et du deutérium des mouvements moléculaires dans l'iodopropyne liquide

1984 ◽  
Vol 62 (6) ◽  
pp. 577-582
Author(s):  
R. Tourki ◽  
F. Fried ◽  
M. J. Seurin ◽  
F. Gaymard ◽  
P. Sixou
Keyword(s):  
Diffusion Model ◽  
Rotational Diffusion ◽  
Relaxation Times ◽  
Spin Rotation ◽  
Proton Relaxation ◽  
Molecular Motions ◽  
Symmetric Top Molecules

Proton and deuterium relaxation times of liquid iodopropyne are measured at various temperatures. The separation of proton relaxation into its main parts, intra- and intermolecular dipolar mechanisms and spin-rotation, is achieved by a dilution study in deuterated iodopropyne. Molecular motions are analyzed by using the rotational diffusion model extended to the case of symmetric top molecules.

Nuclear magnetic resonance relaxation and anisotropic reorientation in liquid dimethylmercury

1977 ◽  
Vol 55 (8) ◽  
pp. 1303-1313 ◽  
Author(s):  
Claude R. Lassigne ◽  
E. J. Wells
Keyword(s):  
Molecular Diffusion ◽  
Symmetry Axis ◽  
Chemical Shift Anisotropy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Spin Lattice ◽  
Resonance Relaxation

Spin–lattice relaxation times of 1H, D, and 199Hg have been measured between 234 and 333 K in liquid dimethylmercury and its isotopic modifications. These measurements have allowed the relaxation mechanisms to be separated. It was found that the spin–rotation interaction is the dominating mechanism for the 199Hg relaxation at 14.1 kG even at low temperatures. We have estimated the spin–rotation constants, [Formula: see text] along with the chemical shift anisotropy [Formula: see text]It is concluded that reorientation about the symmetry axis is not well described by molecular diffusion. Reorientation of the methyl group about its symmetry axis is found to be approximately forty times faster than the reorientation about the perpendicular axis.

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