Synthèse, structure et études spectroscopiques RMN 1H et 13C de dérivés perhydrocyclododéca[b]furaniques

1991 ◽  
Vol 69 (3) ◽  
pp. 521-527 ◽  
Author(s):  
Michel Albrand ◽  
René Dolmazon ◽  
Patrick Pollet
Keyword(s):  
Conformational Analysis ◽  
Force Field ◽  
Key Words ◽  
Molecular Mechanics ◽  
Trans Isomer ◽  
Nmr Spectra ◽  
Synthetic Route ◽  
Force Field Calculations ◽  
Cis Isomer ◽  
C Nmr

A synthetic route to perhydrocyclododeca[b]furan-3-ols, perhydrocyclododeca[b]furan-3-ones, and perhydrocyclododeca[b]furan derivatives is described. Their configurations were determined. For the perhydrocyclododeca[b]furan-3-one and perhydrocyclododeca[b]furan pairs, the cis isomer was much less stable than the trans isomer. This agrees well with results from a conformational analysis, carried out by molecular mechanics. The 1H and l3C NMR spectra are reported. Key words: perhydrocyclododeca[b]furans, conformations, force field calculations, 1H and 13C NMR.

Conformational analysis and complete assignment of the proton and carbon NMR spectra of ouabain and ouabagenin

1990 ◽  
Vol 68 (8) ◽  
pp. 1263-1270 ◽  
Author(s):  
Deane D. McIntyre ◽  
Markus W. Germann ◽  
Hans J. Vogel
Keyword(s):  
Conformational Analysis ◽  
Molecular Mechanics ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
X Ray Diffraction ◽  
Proton Proton ◽  
Proton Coupling ◽  
Nmr Techniques ◽  
Phase Sensitive ◽  
C Nmr

The 1H and 13C NMR spectra of the cardenolide ouabain and its aglycon ouabagenin have been completely assigned by two-dimensional NMR techniques, including phase-sensitive COSY and carbon–proton correlation (HETCOR, HMQC, and COLOC) spectra. The major conformer of these two compounds in solution is all-chair as determined from proton–proton coupling constants and is similar to that in the crystal lattice as previously determined by X-ray diffraction. The conformations of the A and D rings of ouabain in water are somewhat different than in DMSO/CDCl3 (2:1). At lower temperatures (−20 °C) signals from two conformers in slow exchange were readily observed in the 13C spectra, with an approximate ratio of 1:7. Molecular mechanics and dynamics calculations indicate that the conformational process responsible for this involves a chair/twist-boat interconversion of the A ring, with the all-chair conformer highly preferred. Keywords: ouabain, conformational analysis, 2-D NMR, molecular mechanics, molecular dynamics.

scholarly journals Competitive Diels–Alder and ene addition of N-arylmaleimides to 7-dehydrocholesteryl acetate

1992 ◽  
Vol 70 (11) ◽  
pp. 2730-2744 ◽  
Author(s):  
William J. Leigh ◽  
Donald W. Hughes ◽  
D. Scott Mitchell
Keyword(s):  
Molecular Mechanics ◽  
Nmr Spectra ◽  
Benzene Solution ◽  
Diels Alder ◽  
Spectroscopic Techniques ◽  
Two Dimensional ◽  
A Minor ◽  
C Nmr ◽  
Alder Adduct ◽  
Ene Addition

Thermolysis of N-phenyl, N-para-biphenyl, and N-para, para′-terphenylmaleimide with 7-dehydrocholesteryl acetate in benzene solution at 200 °C yields mixtures of four cycloadducts in relative yields that are essentially independent of the maleimide substituent. The three major products are those of ene addition to C7 of the steroid with abstraction of the proton at C9 or C14. The α-endo-Diels-Alder adduct is formed as a minor product. The structures of the adducts have been elucidated on the basis of one- and two-dimensional 1H and 13C NMR spectroscopic techniques, including homonuclear 1H decoupling, NOE, 1H–1H COSY, heteronuclear 1H–13C shift correlation, and TOCSY 2-D experiments, and the results of molecular mechanics (MMX) calculations. The combination of these techniques has made it possible to almost completely assign the 1H and 13C NMR spectra for two of the ene adducts and the Diels–Alder adduct from reaction of 7-dehydrocholesteryl acetate with N-phenyl maleimide.

scholarly journals Reactions of 3-(p-substituted-phenyl)-5-chloromethyl-1,2,4-oxadiazoles with KCN leading to acetonitriles and alkanes via a non-reductive decyanation pathway

2018 ◽  
Vol 14 ◽  
pp. 3011-3017
Author(s):  
Akın Sağırlı ◽  
Yaşar Dürüst
Keyword(s):  
Nmr Spectra ◽  
2D Nmr ◽  
Synthetic Route ◽  
X Ray ◽  
H Nmr ◽  
2D Nmr Spectra ◽  
Tof Ms ◽  
C Nmr

The present work describes an unfamiliar reaction of 5-(chloromethyl)-3-substituted-phenyl-1,2,4-oxadiazoles with KCN affording trisubstituted 1,2,4-oxadiazol-5-ylacetonitriles and their parent alkanes, namely, 1,2,3-trisubstituted-1,2,4-oxadiazol-5-ylpropanes. To the best of our knowledge, the current synthetic route leading to decyanated products will be the first in terms of a decyanation process which allows the transformation of trisubstituted acetonitriles into alkanes by the incorporation of KCN with the association of in situ-formed HCN and most likely through the extrusion of cyanogen which could not be detected or isolated. In addition, the plausible mechanisms were proposed for both transformations. The structures of the title compounds were identified by means of IR, 1H NMR, 13C NMR, 2D NMR spectra, TOF–MS and X-ray measurements.

ChemInform Abstract: CONFORMATIONAL ANALYSIS OF BILE PIGMENTS USING FORCE FIELD CALCULATIONS

1979 ◽  
Vol 10 (51) ◽  
Author(s):  
H. FALK ◽  
G. HOELLBACHER ◽  
O. HOFER
Keyword(s):  
Conformational Analysis ◽  
Force Field ◽  
Bile Pigments ◽  
Force Field Calculations

The importance of conformation in the reactivity of radical cations. Changing configuration at saturated carbon centres

1992 ◽  
Vol 70 (1) ◽  
pp. 272-279 ◽  
Author(s):  
Allyson L. Perrott ◽  
Donald R. Arnold
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Molecular Mechanics ◽  
Radical Cation ◽  
Trans Isomer ◽  
Radical Cations ◽  
Singlet Excited State ◽  
Photostationary State ◽  
Configurational Isomerization ◽  
Cis Isomer

Irradiation of an acetonitrile solution of cis 1-methyl-2-phenylcyclopentane (1bcis); 1,4-dicyanobenzene (2), an electron-accepting photosensitizer; and 2,4,6-collidine (3), a nonnucleophilic base, leads to configurational isomerization of the cyclopentane; the photostationary state lies > 99% in favour of the trans isomer. The mechanism proposed for this reaction involves formation of the radical cation of 1bcis by photoinduced electron transfer to the singlet excited state of 2, deprotonation of the radical cation assisted by the base 3, reduction of the resulting benzylic radical by the radical anion [Formula: see text], and reprotonation of the benzylic anion to give both the cis and the trans isomers of 1b. The photostationary state is controlled by the relative rates of deprotonation of the radical cations of 1bcis and trans; these rates are dependent upon the extent of overlap of the SOMO of the radical cation, which is largely associated with the phenyl ring, and the benzylic carbon–hydrogen bond. Molecular mechanics calculations (MM3 and MMP2) are used to calculate the preferred conformations of the isomers. The required orbital overlap is 31% effective with the global minimum conformation of the cis isomer and essentially ineffective for the low-lying conformations of the trans isomer. This proposed mechanism is supported by Stem–Volmer quenching studies, which indicate that both isomers quench the singlet excited state of 2 at the diffusion-controlled rate, and by deuterium incorporation studies. When irradiation of the cis isomer is carried out in acetonitrile–methanol-O-d as solvent, isomerization is accompanied by deuterium exchange at the benzylic position; the trans isomer is stable under these conditions. Keywords: photosensitized electron transfer, radical cation, deprotonation, configurational isomerization, conformation, molecular mechanics (MM3).

Empirical force field calculations. 10. Conformational analysis of cis-decalin

1981 ◽  
Vol 103 (17) ◽  
pp. 5014-5021 ◽  
Author(s):  
Jan M. A. Baas ◽  
Bastiaan Van de Graaf ◽  
Dirk Tavernier ◽  
Paul Vanhee
Keyword(s):  
Conformational Analysis ◽  
Force Field ◽  
Force Field Calculations ◽  
Empirical Force Field ◽  
Empirical Force Field Calculations

Molecular mechanics (MM2) and conformational analysis of compounds with NCO units. Parametrization of the force field and anomeric effect

1991 ◽  
Vol 12 (1) ◽  
pp. 78-90 ◽  
Author(s):  
Berta Fernández ◽  
Miguel A. Ríos ◽  
Luís Carballeira
Keyword(s):  
Conformational Analysis ◽  
Force Field ◽  
Molecular Mechanics ◽  
Anomeric Effect
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