Orientations of hydroxyl groups. Conformational studies on 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose by nuclear magnetic resonance spectroscopy

1982 ◽  
Vol 60 (13) ◽  
pp. 1648-1656 ◽  
Author(s):  
Photis Dais ◽  
Arthur S. Perlin
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Hydroxyl Group ◽  
Resonance Spectroscopy ◽  
Hydroxyl Groups ◽  
Spectroscopic Techniques ◽  
Relaxation Rates ◽  
Spin Lattice

Various nmr spectroscopic techniques have been used to determine the orientation of the anomeric hydroxyl group of 2,3:5,6-di-O-isopropylidene-α-D-mannofuranose (1) in dimethylsulfoxide solution, as well as other conformational features of themolecule. 13C and 1H coupling constants indicate that in its most probable orientation the O—H bond is anti with respect tocarbon-2, and forms an angle of ~40° with the C-1—H-1 bond. Spin-lattice relaxation rates (R1) and nuclear Overhauser enhancements (nOe) have been measured for the pertinent protons and used, in conjunction with 13C relaxation times, as additional criteria for characterizing the geometry of the anomeric alcohol group of 1. These results are in good agreement with the coupling constant data. The conformations of the mannofuranose ring, the 2,3-O-isopropylidene ring, and the C-4 to C-6 region of the molecule are also described.

Boron-11, boron-10, and nitrogen-14 NMR relaxation rates and quadrupole coupling constants in BH3NH3

1992 ◽  
Vol 70 (9) ◽  
pp. 2420-2423 ◽  
Author(s):  
Glenn H. Penner ◽  
Stephen I. Daleman ◽  
Angela R. Custodio
Keyword(s):  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Orbital Theory ◽  
Spin Lattice ◽  
Quadrupolar Coupling ◽  
Field Gradients

The 11B, 10B, and 14N spin–lattice relaxation times (T1) for aqueous solutions of BH3NH3 were measured by NMR spectroscopy. The results of this investigation are consistent with the nuclear quadrupolar coupling constants reported in previous nuclear quadrupolar resonance and microwave studies. The activation energy associated with rotational reorientation of BH3NH3 in aqueous solution is 11.7 ± 0.6 kJ/mol. Electric field gradients were calculated at various levels of abinitio molecular orbital theory, in order to obtain theoretical 14N and 11B quadrupolar coupling constants. At the highest level of calculation (CI(SD)/6-31G**//MP2/6-31G**), these are in agreement with recently reported microwave results but not with previously reported NQR experiments.

scholarly journals Methyl Group Rotation and Tunnellingin Crystals of 5-Membered Ring Molecules

1988 ◽  
Vol 43 (1) ◽  
pp. 35-42 ◽  
Author(s):  
A.-S. Montjoie ◽  
W. Müller-Warmuth ◽  
Hildegard Stiller ◽  
J. Stanislawski
Keyword(s):  
Elevated Temperatures ◽  
Inelastic Neutron Scattering ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Quantum Tunnelling ◽  
Spin Lattice

Abstract1H NMR spin-lattice relaxation times T1 and -if accessible -level-crossing peaks and inelastic neutron scattering spectra have been measured for solid 2-and 3-methylfuran, 2-and 3-methylthiophene, 3-and 4-methylpyrazole, 1-methylimidazole, and 5-methylisoxazole. From the tunnel splittings, the torsional excitations and the NMR relaxation rates, the molecular dynamics of the methyl rotators has been evaluated between the limits of quantum tunnelling at low temperatures and thermally activated random reorientation at elevated temperatures.

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.

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

The conformational equilibrium in [13C-1-methyl]-cis-1,4-dimethylcyclohexane

1980 ◽  
Vol 58 (23) ◽  
pp. 2709-2713 ◽  
Author(s):  
Harold Booth ◽  
Jeremy Ramsey Everett
Keyword(s):  
Conformational Equilibrium ◽  
Chemical Shifts ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Nuclear Overhauser ◽  
In Cis ◽  
C Nmr

The conformational equilibrium in [13C-1-methyl]-cis-1,4-dimethylcyclohexane has been assessed by (a) direct integration of signals due to equatorial and axial methyl carbons in the 13C nmr spectrum at 172 K and (b) by measurement of the 13C chemical shifts of C-1 and C-4 in the spectrum at 300 K. It is concluded that a 13C isotope effect on the position of the degenerate equilibrium in cis-1,4-dimethylcyclohexane is either nonexistent, or is too small to be detected by methods of analyses employed. The 13C nmr data incidental to the study (chemical shifts, coupling constants, spin–lattice relaxation times, nuclear Overhauser enhancements, and 1-bond isotope shifts) are recorded for the title compound and its trans-isomer.

Application of the relaxation reagent Gd(FOD)3 (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate)gadolinium(III) in 1H NMR spectroscopy of adamantoid compounds

1979 ◽  
Vol 44 (2) ◽  
pp. 533-541
Author(s):  
Jiří Karhan ◽  
Milan Hájek ◽  
Zbyněk Ksandr ◽  
Luděk Vodička
Keyword(s):  
Nmr Spectroscopy ◽  
Structure Analysis ◽  
1H Nmr Spectroscopy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Shift Reagent ◽  
Spin Lattice Relaxation ◽  
Reagent Concentration ◽  
Relaxation Rates ◽  
Spin Lattice

This spin-lattice relaxation times T1 of protons in the presence of the shift reagent Eu(FOD)3-D27 and the relaxation reagent Gd(FOD)3 were employed for the structure analysis of 1-adamantanol, 4-diamantanol, adamantanone, and 2,2-dioxy-2-thiaadamantane. The structure models of the complex adducts of the substrates with Gd(FOD)3 are discussed. The dependence of the corrected spin-lattice relaxation rates on the relaxation reagent concentration is linear only in the region of low concentration.

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