Orientation of the methoxyl group in cis- and trans-2-methoxy-4-methyl-1,3-dioxanes and related compounds as inferred by 1H and 13C nmr spectroscopy. The significance of the "exo-anomeric" effect

1982 ◽  
Vol 60 (9) ◽  
pp. 1067-1072 ◽  
Author(s):  
Vanga S. Rao
Keyword(s):  
Dynamic Equilibrium ◽  
Chemical Shifts ◽  
13C Nmr Spectroscopy ◽  
Methoxyl Group ◽  
Anomeric Effect ◽  
1H And 13C Nmr ◽  
Nuclear Overhauser ◽  
Cis And Trans ◽  
In Cis ◽  
Related Compounds

Carbon-13 chemical shifts and 13C—1H couplings are reported for some substituted 2-methoxy-1,3-dioxanes and related tetrahydropyran derivatives. These data, together with nuclear Overhauser enhancement experiments, provided evidence for a favored orientation of the methoxyl group. From an analysis of the 13C chemical shifts and the magnitude of vicinal 13C—1H coupling between —OCH3 and H-2, a possible dynamic-equilibrium orientation for the methoxyl group is proposed, and an evaluation of the significance of a "generalized exo-anomeric effect" is presented.

The conformational preference of methoxyl and acetoxyl groups in 3-oxycyclohexenes, 2-oxymethylenecyclohexanes, and 1-oxytetralins and the generalized anomeric effect

1987 ◽  
Vol 65 (8) ◽  
pp. 1761-1768 ◽  
Author(s):  
Adama Ouédraogo ◽  
Minh Tan Phan Viet ◽  
John K. Saunders ◽  
Jean Lessard
Keyword(s):  
Methoxyl Group ◽  
Equatorial Orientation ◽  
Anomeric Effect ◽  
Conformational Preference ◽  
Magnetic Resonance Data ◽  
Conformational Effect ◽  
Axial Conformer ◽  
Resonance Data ◽  
Cis And Trans ◽  
Derivatives Of

The 13C and 1H nuclear magnetic resonance data of 3-oxycyclohexenes, 2-oxymethylenecyclohexanes, and 1-oxytetralins show (i) that the pseudoaxial preference is larger for the acetoxyl group than for the methoxyl group in 3-oxycyclohexenes, (ii) that the methoxyl and the acetoxyl groups have the same pseudoaxial preference in 1-oxytetralins, and (iii) that in 2-oxymethylenecyclohexanes, the acetoxyl group prefers the equatorial orientation whereas the methoxyl group prefers to be axial. These results are interpreted in terms of the orbital picture (π–σ* stabilization of the axial conformer) of the generalized anomeric effect to which is opposed a conformational effect termed the "unsaturation effect" in 2-acetoxymethylenecyclo-hexane and probably also, but to a much smaller extent, in 1-acetoxytetralin. The results also show that cis and transtert-butyl analogues of 3-oxycyclohexenes do not represent the true limit conformers whereas cis and trans 4-tert-butyl derivatives of 2-oxymethylenecyclohexanes do not differ drastically from the limit conformers.

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.

Tungsten-183 chemical shifts in cis- and trans-bis(tributylphosphine)tetracarbonyltungsten

1971 ◽  
Vol 10 (1) ◽  
pp. 206-207 ◽  
Author(s):  
Paul Joseph Green ◽  
Thomas Henderson Brown
Keyword(s):  
Chemical Shifts ◽  
Cis And Trans ◽  
In Cis

scholarly journals SYNTHESIS OF PROPERTIES N-METHYL-2-(PYRID-4-YL)-3,4-FULLEROPYRROLIDINE

2020 ◽  
Vol 2 (440) ◽  
pp. 62-68
Author(s):  
S.D. Fazylov ◽  
O.A. Nurkenov ◽  
A.E. Arinova ◽  
T.M. Seilkhanov ◽  
A.M. Gazaliev ◽  
...  
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Wide Spectrum ◽  
13C Nmr Spectroscopy ◽  
Fullerene C60 ◽  
Water Soluble ◽  
1H And 13C Nmr ◽  
Integrated Intensity ◽  
Pharmacophore Group

The article is devoted to the reactions of [2+3] cycloaddition of pyridine-4-aldehyde to fullerene C60, as well as to the preparation of its water-soluble from of the resulting reaction product N-methyl-2-(pyrid-4-yl)-3,4-fulleropyrrolidine. A literature review of organic compounds containing the pyrrolidine cycle was carried out. It is noted that such compounds have a wide spectrum of biological activity and are part of many drugs of both natural and synthetic origin. In this regard, an interesting “pharmacophore” group is the pyridine cycle, which is part of about 5% of all known drugs. The reaction of pyridin-4-aldehyde with fullerene C60 was carried out in the presence of sarcosine under the conditions of the Prato reaction. The reaction mechanism of 1,2-dipolar cycloaddition, leading to fulleropyrrolidine, is described. The water-soluble complex fulleropyrrolidinas with poly-N-vinylpyrrolidone was obtained. The structures of the synthesized compounds were studied by IR, UV, 1H and 13C NMR spectroscopy, as well as by the date of two-dimensional spectra of COSY (1H-1H) and HMQC (1H-13H). The values of chemical shifts, multiplicity and integrated intensity of 1H and 13C NMR signals in one-dimensional NMR spectra were determined. Using spectra in the formats COSY (1H-1H) and HMQC (1H-13C) homo- and heteronuclear interaction were established, confirming the structure of the studied compounds. Key words: fullerene C60, sarcosine, pyridine-4-aldehyde, fulleropyrrolidines, Prato reaction, NMR spectra.

Cis–Trans Conformational Dependence of the Carboxylate pK in Glycylsarcosine

1974 ◽  
Vol 52 (12) ◽  
pp. 2348-2352 ◽  
Author(s):  
R. A. Morton ◽  
S. S. Danyluk
Keyword(s):  
Chemical Shift ◽  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Molecular Models ◽  
Amino Groups ◽  
Cis And Trans ◽  
In Cis ◽  
Cis Isomer

A study is reported of the influence of pD upon the 220 MHz proton n.m.r. spectrum of the dipeptide glycylsarcosine (Gly-Sar) in D2O at 23 °C. Variation of pD produces characteristic changes in chemical shifts for Gly-Sar and an analysis of the pD–chemical shift curves shows that the carboxyl pK differs significantly in cis and trans conformers, having values of 3.01 ± 0.03 and 3.39 ± 0.03, respectively. From a consideration of molecular models and theoretical calculations, it is concluded that the pK difference arises from a closer juxtaposition of terminal carboxyl and amino groups in the cis isomer.

A dynamic NMR study of the nitrogen lone pair orientation in 2-benzoyl-5-methyl-5-aza-1,3-dithiacyclohexane

1989 ◽  
Vol 67 (12) ◽  
pp. 2067-2070 ◽  
Author(s):  
B. Mario Pinto ◽  
Blair D. Johnston ◽  
Ruby Nagelkerke ◽  
Eusebio Juaristi ◽  
Eduardo A. González
Keyword(s):  
Magnetization Transfer ◽  
Lone Pair ◽  
Anomeric Effect ◽  
Saturation Transfer ◽  
Nuclear Overhauser Enhancement ◽  
Free Energy Of Activation ◽  
Nmr Study ◽  
Nitrogen Lone Pair ◽  
Nuclear Overhauser ◽  
Related Compounds

Nuclear Overhauser enhancement difference experiments and magnetization transfer experiments on 2-benzoyl-5-methyl-5-aza-1,3-dithiacyclohexane 1 at 186 K show conclusively that the N-methyl group adopts a preferred axial orientation. The result has implications for evaluation of the origin of the anomeric effect in this and related compounds. The free energy of activation for ring interconversion in 1 is estimated by spin saturation transfer experiments to be 10.7 ± 0.4 kcal mol−1. Keywords: D NMR, conformational analysis, nuclear Overhauser enhancement, saturation transfer.

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