Déplacements homolytiques intramoléculaires. 19. Stéréochimie de la décomposition induite de peroxydes insaturés conduisant à la formation d'hétérocycles à trois et quatre chaînons

1991 ◽  
Vol 69 (8) ◽  
pp. 1320-1325 ◽  
Author(s):  
X. Lubeigt ◽  
F. Flies ◽  
M. J. Bourgeois ◽  
E. Montaudon ◽  
B. Maillard
Keyword(s):  
Key Words ◽  
Homolytic Decomposition ◽  
Homolytic Substitution ◽  
C Nmr

Homolytic decomposition induced by addition of dichloromethyl radicals to β- and γ-unsaturated peroxides having a substituent on the chain linking the unsaturation and the peroxide function was studied. The stereochemistry of the heterocycles produced was determined by I3C NMR and the stereoselectivity of intramolecular homolytic substitution on the peroxidic bond discussed. Key words: unsaturated peroxides, homolytic intramolecular substitutions, radical additions, oxygenated heterocycles.

Ligand scrambling reactions of cyano(thione)gold(I) complexes and determination of their equilibrium constants

2002 ◽  
Vol 80 (10) ◽  
pp. 1279-1284 ◽  
Author(s):  
Saeed Ahmad ◽  
Anvarhusein A Isab ◽  
Herman P Perzanowski
Keyword(s):  
Ionic Strength ◽  
Nmr Spectroscopy ◽  
Key Words ◽  
Equilibrium Constants ◽  
Solvent Polarity ◽  
Approach To Equilibrium ◽  
Initial Concentration ◽  
C Nmr

Ligand scrambling reactions in cyano(thione)gold(I) complexes ([>C=S-Au-CN]) to form [Au(>C=S)2]+ and [Au(CN)2]– species have been investigated for a series of thiones in DMSO using 13C and 15N NMR spectroscopy. Rapid approach to equilibrium occurred and resulted in distinct signals for the [>C=S-Au-CN] and [Au(CN)2]– complexes, both in 13C and 15N NMR. Equilibrium constants (Keq) were determined for scrambling of all the complexes by integrating the CN resonances in the 13C NMR recorded at 298 K. The influence of various factors (initial concentration, ionic strength, temperature, and solvent polarity) on the Keq value was examined for a representative complex (ImtAuCN (Imt = Imidazolidine-2-thione)).Key words: cyanogold(I) complexes, thiones, ligand scrambling, NMR, Keq.

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.

Synthesis and X-ray structures of amidinate, oxoamidate, and thioamidate complexes of boron

2000 ◽  
Vol 78 (1) ◽  
pp. 10-15 ◽  
Author(s):  
Pierre Blais ◽  
Tristram Chivers ◽  
Andrew Downard ◽  
Masood Parvez
Keyword(s):  
Key Words ◽  
Mass Spectra ◽  
Molar Ratio ◽  
Monoclinic Space Group ◽  
Crystal Data ◽  
Space Group ◽  
X Ray ◽  
Bonding Mode ◽  
C Nmr

The reactions of PhBCl2 with Li[CE(NtBu)(nBu)] or Li[CS(NtBu)(NHtBu)] (1:1 molar ratio) in toluene at 23°C produced the heterocycles Ph(Cl)B(μ-NtBu)(μ-E)C(nBu) (1a, E = NtBu; 1b, E = O; 1c, E = S) or Ph(Cl)B(μ-NtBu)(μ-S)C(NHtBu) (2), which were characterized by 1H, 11B and 13C NMR and by mass spectra. X-ray structural determinations revealed that 1a, 1c and 2 contain four-membered rings. In 2 the thioamidate ligand adopts an N,S bonding mode. Crystal data: 1a, monoclinic, space group P21, a = 8.816(3), b = 11.311(2), c = 10.168(3) Å, β = 98.86(3)°, V = 1001.7(5) Å3, Z = 2, R = 0.042, and Rw = 0.020; 1c, monoclinic, space group P21/n, a = 7.617(2), b = 11.200(1), c = 19.568(2), β = 90.74(2)°, V = 1669.1(5) Å3, Z = 4, R = 0.046, and Rw = 0.059; 2, monoclinic, space group P21/a, a = 11.357(2), b = 12.289(2), c = 12.620(3) Å, β = 95.43(2)°, V = 1753.4(5) Å3, Z = 4, R = 0.043, and Rw = 0.027. Key words: boron, amidinate, oxoamidate, thioamidate, X-ray structures.

Inhibition of papain by peptide nitriles: conversion of the nitrile group into other functionalities via the papain:nitrile thioimidate ester adduct

1991 ◽  
Vol 69 (8) ◽  
pp. 1288-1297 ◽  
Author(s):  
Barbara J. Gour-Salin ◽  
Paule Lachance ◽  
Andrew C. Storer
Keyword(s):  
Amino Acid ◽  
Key Words ◽  
Active Site ◽  
Nitrile Group ◽  
Reversible Inhibitors ◽  
Nmr Techniques ◽  
Acid Nitrile ◽  
C Nmr

Peptide nitriles are reversible inhibitors of papain that form thioimidates with the cysteine thiol in the enzyme's active site. These thioimidates undergo reactions with thiols and amines to form acids and amidines, respectively. These reactions were also found to be stereospecific. Only a thioimidate derived from an L-amino acid nitrile will react with exogenous nucleophiles. These reactions were followed by 13C and 15N NMR techniques. Key words: papain, nitrile, l3C NMR, 15N NMR, thioimidate.

Oxidative fluorination in the Ph2SO–XeF2–Cl− system and fluorine exchange in the Ph2S(O)F2–Ph2S(O)F+ system

1996 ◽  
Vol 74 (11) ◽  
pp. 2002-2007 ◽  
Author(s):  
Xiaobo Ou ◽  
Alexander F. Janzen
Keyword(s):  
Nmr Spectroscopy ◽  
Ab Initio ◽  
Key Words ◽  
Exchange Process ◽  
Chloride Ion ◽  
Fluoride Ion ◽  
Molecular Orbital Calculations ◽  
Xenon Difluoride ◽  
Mild Conditions ◽  
C Nmr

Oxidative fluorination of diphenyl sulfoxide with xenon difluoride occurs under mild conditions in the presence of chloride ion to give Ph2S(O)F2 in quantitative yield. Chloride ion appears to react with xenon difluoride to generate fluoride ion, and a mechanism of oxidative fluorination is proposed that involves anionic Ph2S(O)F− and radical Ph2S(O)F• intermediates. Addition of cationic Ph2S(O)F+ to Ph2S(O)F2 initiates rapid fluorine exchange, presumably via a symmetrical fluorine-bridged intermediate, and this exchange process was monitored by 13C and 19F NMR spectroscopy. In the presence of chloride ion, Ph2S(O)Cl2 is formed and can be identified by 13C NMR and by its hydrolysis to Ph2SO2. Mechanisms are proposed for these reactions, and ab initio molecular orbital calculations (GAUSSIAN92) were carried out of the postulated intermediates. Key words: preparation of Ph2S(O)F2, Ph2S(O)F+, and Ph2S(O)Cl2; oxidative fluorination in the Ph2SO–XeF2–Cl− system; fluorine exchange in the Ph2S(O)F2–Ph2S(O)F+ system.

Synthetic conversion of bryostatin 2 to bryostatin 1 and related bryopyrans

1991 ◽  
Vol 69 (5) ◽  
pp. 856-860 ◽  
Author(s):  
George R. Pettit ◽  
Dipanjan Sengupta ◽  
Cherry L. Herald ◽  
Nancy A. Sharkey ◽  
Peter M. Blumberg
Keyword(s):  
Natural Products ◽  
Key Words ◽  
Hydroxyl Group ◽  
Bryostatin 1 ◽  
Nmr Studies ◽  
Selective Protection ◽  
Selective Conversion ◽  
C Nmr

Bryostatin 2 (1a) has been converted to bryostatin 1 (1e) and bryostatin 12 (1i) by a selective protection and deprotection involving the C-26 hydroxyl group. The new bryostatins 1g,1k, and 1m were also prepared starting from bryostatin 2. The C-7 substituents of natural bryostatins 4 and 5 were revised from isovalerate → pivalate employing comparative 1H and 13C NMR studies of the semi-synthetic bryostatins 1k and 1m and the natural products. Key words: bryostatin 2 → 1, selective conversion, bryostatins 4 and 5, pivalates.

Negative hyperconjugation in hexachloro-3-cyclopentenylaminosulphenyl halides: Preparation and X-ray structure of C5Cl6NSBr and synthesis of C5Cl6NS+AsF6−

1991 ◽  
Vol 69 (6) ◽  
pp. 1022-1027 ◽  
Author(s):  
Allen Apblett ◽  
Tristram Chivers ◽  
James F. Fait ◽  
Rainer Vollmerhaus
Keyword(s):  
Crystal Structure ◽  
Key Words ◽  
Good Yield ◽  
Variable Temperature ◽  
Triclinic Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Compound C ◽  
Negative Hyperconjugation ◽  
C Nmr

The reaction of hexachlorocyclopentadiene with (NSCl)3 at 65 °C in the absence of a solvent produced hexachloro-3-cyclopentenylidenaminosulfenyl chloride, C5Cl6NSCl, in good yield. The derivatives C5Cl6NSX(X = Br, I, C5Cl6N, NPr2i, Ph) were prepared by treatment of C5Cl6NSCl with Me3SiBr, Me3SiI, Ph3Sb, iPr2NH, and Ph2Hg, respectively. The crystal structure of C5Cl6NSBr was determined by X-ray crystallography. Crystals of C5Cl6NSBr are triclinic, space group [Formula: see text] with a = 9.626(2), b = 9.810(2), c = 13.736(2) Å, α = 79.68(1), β = 88.62(1), γ = 74.73(1)°, Z = 4, final R and Rw values were0.075 and 0.063, respectively, for 4850 unique observed reflections. The > C=NSBr moiety adopts a syn conformation and there are two different molecules of C5Cl6NSBr in the asymmetric units. The bond lengths are d(C=N) = 1.278(8) and 1.253(8), d(N—S) = 1.560(6) and 1.569(6), and d(S—Br) = 2.229(2) and2.235(2) Å. The bond angles at nitrogen are 146.7(4) and 148.6(4) and those at sulfur are 116.8(2) and 116.5(2)°. The unusual geometry of the < C=NSBr moiety is explained in terms of negative hyperconjugation (nN → σSBr*). A variable temperature 13C NMR of C5Cl6NSCl provides evidence for a fiuxional process (ΔG*298 = 68.1 ± 1.2 kJ mol−1) in solution. The dark purple compound C5Cl6NS+AsF6− was synthesized from the reaction of C5Cl6NSCl and AgAsF6 in SO2. Key words: hexachloro-3-cyclopentenylidenamino sulfides, crystal structure, hexachloro-3-cyclopentenylidenaminosulfenyl bromide.

Synthesis and nuclear magnetic resonance spectroscopy of indane structures: indanes mono- and disubstituted in the pentagonal ring

1991 ◽  
Vol 69 (7) ◽  
pp. 1166-1170 ◽  
Author(s):  
Elba N. Alesso ◽  
Dora G. Tombari ◽  
Adriana F. Ibañez ◽  
Graciela Y. Moltrasio Iglesias ◽  
José M. Aguirre
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Key Words ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
C Nmr ◽  
Nuclear Magnetic

Indanes monosubstituted and 1,2- and 1,3-disubstituted in the pentagonal ring were synthesized, and configurations were assigned to the 1,2-disubstituted compounds by means of nuclear magnetic resonance spectroscopy. Key words: mono- and disubstituted indanes, conformation, configuration, 1H and 13C NMR, synthesis.

Synthesis, IR, and multinuclear NMR spectroscopic studies of complexes of the type cis- and trans-Pt(amine)2(NO3)2

2004 ◽  
Vol 82 (4) ◽  
pp. 524-532 ◽  
Author(s):  
Fernande D Rochon ◽  
Viorel Buculei
Keyword(s):  
Key Words ◽  
Secondary Amine ◽  
Spectroscopic Studies ◽  
Coupling Constants ◽  
Primary Amines ◽  
Trans Isomers ◽  
H Nmr ◽  
Cis And Trans ◽  
Ir Bands ◽  
C Nmr

Compounds of the types cis- and trans-Pt(amine)2NO3)2 have been synthesized and characterized by IR and multinuclear (195Pt, 13C, and 1H) NMR spectroscopies. The nitrato IR bands were compared for the two isomers. The 195Pt NMR resonances of the trans complexes were observed at lower fields (avg. –1570 ppm for primary amines) than the cis analogues (avg. –1698 ppm) for an average Δδ value of 124 ppm. The complexes containing a secondary amine were observed at about the same field for the cis isomers (avg. –1682 ppm) and surprisingly at much higher fields for the trans compounds (avg. –1638 ppm). In 1H NMR, the coupling constants 2J(195Pt-1HN) are larger for the cis isomers (avg. 67 Hz) than for the trans compounds (avg. 58 Hz). The 3J(195Pt-1H) are also larger for the cis complexes (avg. 40 vs. 33 Hz). In 13C NMR, the coupling constants are also geometry dependent. The 3J(195Pt-13C) are larger for the cis isomers (avg. 37 Hz) than for the trans compounds (avg. 28 Hz). The 2J(195Pt-13C) are much smaller (avg. 18 Hz for the cis complexes and 16 Hz for the trans isomers).Key words: platinum, amine, nitrato, NMR, IR.

On the cross-sectional shape of the cellulose crystallites in the tunicate Halocynthia papillosa

1990 ◽  
Vol 48 (3) ◽  
pp. 566-567
Author(s):  
J.-F. Revol ◽  
Y. Van Daele ◽  
F. Gaill
Keyword(s):  
Contrast Imaging ◽  
Animal Kingdom ◽  
Bright Field ◽  
Field Mode ◽  
Cross Sectional ◽  
Ultrathin Sections ◽  
The Cross ◽  
Sectional Shape ◽  
Valonia Ventricosa ◽  
C Nmr

The only form of cellulose which could unequivocally be ascribed to the animal kingdom is the tunicin that occurs in the tests of the tunicates. Recently, high-resolution solid-state l3C NMR revealed that tunicin belongs to the Iβ form of cellulose as opposed to the Iα form found in Valonia and bacterial celluloses. The high perfection of the tunicin crystallites led us to study its crosssectional shape and to compare it with the shape of those in Valonia ventricosa (V.v.), the goal being to relate the cross-section of cellulose crystallites with the two allomorphs Iα and Iβ.In the present work the source of tunicin was the test of the ascidian Halocvnthia papillosa (H.p.). Diffraction contrast imaging in the bright field mode was applied on ultrathin sections of the V.v. cell wall and H.p. test with cellulose crystallites perpendicular to the plane of the sections. The electron microscope, a Philips 400T, was operated at 120 kV in a low intensity beam condition.

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