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.

Conformation of ring A in triterpenoid ketones. Carbon-13 chemical shifts and spin-lattice relaxation times of lupane and 18α-oleanane derivatives

1989 ◽  
Vol 54 (7) ◽  
pp. 1928-1939 ◽  
Author(s):  
Miloš Buděšínský ◽  
Jiří Klinot
Keyword(s):  
Chemical Shifts ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Chair Conformation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Structural Assignment ◽  
Boat Form ◽  
The One ◽  
C Nmr

13C NMR spectra of sixteen lupane and 19β,28-epoxy-18α-oleanane triterpenoids I-XVI were measured and a complete structural assignment of chemical shifts was made. For most compounds also the carbon spin-lattice relaxation times T1 were obtained. Characteristic differences in chemical shifts of some carbon atom signals were found between 2α-methyl-3-oxo and 2α-methyl-1-oxo derivatives II, V and VIII with chair conformation of the ring A on the one hand and their 2β-isomers III, VI and IX (boat form) on the other. Using these 2-methyl ketones as models, the chair-boat population in allobetulone (I), 3-oxo-28-lupanenitrile (IV) and 1-oxo derivative VII was determined. The results agree well with the data obtained by other physical methods.

Keto-Enol Tautomerism of Dimedone Studied by Dynamic NMR

1996 ◽  
Vol 50 (11) ◽  
pp. 1408-1412 ◽  
Author(s):  
Antonio Martínez-Richa ◽  
Guillermo Mendoza-Díaz ◽  
Pedro Joseph-Nathan
Keyword(s):  
High Resolution ◽  
Chemical Shifts ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Tautomeric Equilibrium ◽  
Spin Lattice Relaxation ◽  
Exponential Factor ◽  
Spin Lattice ◽  
C Nmr ◽  
Coalescence Temperature

The keto-enol tautomeric equilibrium of dimedone has been investigated by high-resolution 13C NMR spectroscopy. Kinetic information of the solution keto-enol tautomerism for dimedone in DMSO, in the temperature range of 25–85 °C, was derived from line shape measurements in a 75-MHz spectrometer. A value of 3.43 Kcal/mol was found for the Arrhenius activation energy Ea and of 1.07 × 106 s−1 for the pre-exponential factor A. With the use of the observed chemical shifts in the high-resolution 13C-NMR spectra of dimedone in the solid state, an estimate coalescence temperature of 240 K for dimedone in DMSO was obtained by extrapolation of the experimental curve. The estimated free energy of activation at the coalescence temperature, Δ Gc≠, is 10.8 Kcal/mol. Finally, the 13C spin-lattice relaxation times, T1(13C), in solid dimedone were measured as a function of temperature in the range of 25 to 90 °C. The data are discussed in terms of the different motional environments that result from the geometric restrictions imposed by hydrogen bonding in the crystal structure.

1H–1H internuclear distance measurements in carbohydrates: proton transient nuclear Overhauser enhancement and spin-lattice relaxation in (13C)- and (2H)-substituted compounds

1990 ◽  
Vol 68 (12) ◽  
pp. 2171-2182 ◽  
Author(s):  
Paul C. Kline ◽  
Anthony S. Serianni ◽  
Shaw-Guang Huang ◽  
Michael Hayes ◽  
Robert Barker
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Lattice Relaxation ◽  
Substitution Effects ◽  
Distance Measurements ◽  
Spin Lattice ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser

Proton transient nuclear Overhauser enhancement (TnOe) and spin-lattice relaxation times (T1) have been used to evaluate the conformations of several monosaccharides and disaccharides containing (13C) and (2H) substitution. Absolute 1H–1H internuclear distances were determined by TnOe and DESERT (deuterium substitution effects on relaxation times) experiments on conformationally rigid methyl β-D-galactopyranoside and α- and β-D-xyloses, respectively. The DESERT method was extended to examine O-glycoside conformation in two blood-group disaccharides that were prepared enzymically with (13C) and (or) (2H) substitution. Preferred disaccharide conformations deduced from these distance measurements are compared to those determined from 13C–13C and 13C–1H spin coupling constants, theoretical calculations, and crystallographic studies. Keywords: TnOe, DESERT, carbohydrate conformation.

Germanium-73 chemical shifts and spin-lattice relaxation times of some tetrasubstituted germanes

1984 ◽  
Vol 23 (23) ◽  
pp. 3835-3836 ◽  
Author(s):  
Yoshito Takeuchi ◽  
Toshie Harazono ◽  
Norihiro Kakimoto
Keyword(s):  
Chemical Shifts ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice

Synthesis of sugar-organometallic conjugales: ferrocenyl monosaccharide derivatives

1980 ◽  
Vol 58 (12) ◽  
pp. 1188-1197 ◽  
Author(s):  
Michael J. Adam ◽  
Laurance D. Hall
Keyword(s):  
Group Technology ◽  
Chemical Shifts ◽  
Soluble Sugar ◽  
Free Water ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Water Soluble ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice

Suitably blocked carbohydrates containing free thio 4, amino 5, and hydroxyl 10, 19 nucleophilic functionalities have been treated with (a) ferrocenecarbonyl chlorides 2 and 3, (b) N,N-dimethylaminomethylferrocene methiodide 12, and (c) ferrocenyl tosylate 16 to form the ferrocenyl sugar derivatives 6, 7, 8, 9, 11, 13, 14, 15, and 20. Direct conjugation of a free, water-soluble sugar to ferrocene was achieved by the formation of a Schiff's base between glucosamine hydrochloride 25 and ferrocene carboxaldehyde 24. The synthesis of ferrocenyl sugars using bridging group technology is exemplified by the conjugation of the thio sugar 4 to ferrocene via the versatile coupling reagent cyanuric chloride 21 to form the s-triazine compound 23. These products have been studied by 1H nmr spectroscopy: chemical shifts, coupling constants, and proton spin–lattice relaxation measurements.

scholarly journals N.m.r. and molecular-modelling studies of the solution conformation of heparin

1993 ◽  
Vol 293 (3) ◽  
pp. 849-858 ◽  
Author(s):  
B Mulloy ◽  
M J Forster ◽  
C Jones ◽  
D B Davies
Keyword(s):  
Molecular Modelling ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Conformational Energy Calculations ◽  
Molecular Modelling Studies ◽  
Modelling Studies ◽  
Modelling Techniques ◽  
Nuclear Overhauser

The solution conformations of heparin and de-N-sulphated, re-N-acetylated heparin have been determined by a combination of n.m.r. spectroscopic and molecular-modelling techniques. The 1H- and 13C-n.m.r. spectra of these polysaccharides have been assigned. Observed 1H-1H nuclear Overhauser enhancements (n.O.e.s) have been simulated using the program NOEMOL [Forster, Jones and Mulloy (1989) J. Mol. Graph. 7, 196-201] for molecular models derived from conformational-energy calculations; correlation times for the simulations were chosen to fit experimentally determined 13C spin-lattice relaxation times. In order to achieve good agreement between calculated and observed 1H-1H n.O.e.s it was necessary to assume that the reorientational motion of the polysaccharide molecules was not isotropic, but was that of a symmetric top. The resulting model of heparin in solution is similar to that determined in the fibrous state by X-ray-diffraction techniques [Nieduszynski, Gardner and Atkins (1977) Am. Chem. Soc. Symp. Ser. 48, 73-80].

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.

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