Carbon-carbon coupling of 4,6-dinitrobenzofuroxan with 3-aminothiophenes: a kinetic and structural study

1998 ◽  
Vol 76 (6) ◽  
pp. 937-945 ◽  
Author(s):  
François Terrier ◽  
Marie-José Pouet ◽  
Khalid Gzouli ◽  
Jean-Claude Hallé ◽  
Francis Outurquin ◽  
...  
Keyword(s):  
Negative Charge ◽  
Dilute Acid ◽  
Amino Groups ◽  
Nmr Studies ◽  
Carbon Nucleophiles ◽  
Nmr Data ◽  
Potentiometric Measurements ◽  
Nucleophilic Reactivity ◽  
Negative Charge Density ◽  
C Nmr

Potentiometric measurements carried out in a 50-50 (v/v) H2O-Me2SO mixture together with 1H and 13C NMR studies carried out in pure Me2SO-d6 reveal that 3-aminothiophene (4a), 3-N-(methylamino)thiophene (4b), and 3-N,N-dimethylaminothiophene (4c) undergo protonation exclusively at the amino groups in dilute acid solutions. The pKa values of 4a, 4b, and 4c are equal to 3.38, 3.65, and 3.53, respectively, at 25°C, comparing well with those for related anilines in the same aqueous Me2SO mixtures. However, despite this similarity of the nitrogen basicities, compounds 4a, 4b, and 4c are found to behave differently from anilines upon treatment with super-electrophilic 4,6-dinitrobenzofuroxan (DNBF). While anilines react to give first an N-bonded sigma -adduct that subsequently decomposes to afford the thermodynamically more stable C-bonded adduct, the 3-aminothiophenes react only as carbon nucleophiles, giving rise directly to the corresponding C-adducts. Based on 1H and 13C NMR data as well as measurements of the rate constants (k1DNBF) for DNBF addition to 4a, 4b, and 4c, it is demonstrated that 3-aminothiophenes possess such high negative charge density at C-2 that they can be regarded as strongly enaminic in nature. Estimates of the pKa values for protonation at C-2 of 4a, 4b, and 4c could be made: pKa4a approx -0.4; pKa4b approx 0.2; pKa4c approx 0.8. Thus, these compounds are more susceptible to electrophilic addition at this position than most of the five-membered ring heterocycles studied so far. Altogether, the results demonstrate the importance of the hyper-ortho relationship in the thiophene systems, accounting for the ease of both electrophilic and nucleophilic reactivity of 3-X-thiophenes in σ -complex formation processes.Key words: aminothiophenes, enamines, superelectrophiles, dinitrobenzofuroxan, hyper-ortho relationship.

scholarly journals Structural Investigations of C-Nitrosobenzenes. Part 3.1 Solid-state and Solution 13C NMR Studies, and Crystal Structure of E-(4-CIC6H4NO)2

1999 ◽  
Vol 23 (3) ◽  
pp. 202-203
Author(s):  
Daniel A. Fletcher ◽  
Brian G. Gowenlock ◽  
Keith G. Orrell ◽  
David C. Apperley ◽  
Michael B. Hursthouse ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
13C Nmr ◽  
Nmr Studies ◽  
Structural Investigations ◽  
Nmr Data ◽  
C Nmr

Solid-state and solution 13C NMR data for the monomers and dimers of 3- and 4-substituted nitrosobenzenes, and the crystal structure of E-(4-CIC6H4NO)2 are reported.

scholarly journals Characterization of Cerebral Glutamine Uptake from Blood in the Mouse Brain: Implications for Metabolic Modeling of 13C NMR Data

2014 ◽  
Vol 34 (10) ◽  
pp. 1666-1672 ◽  
Author(s):  
Puneet Bagga ◽  
Kevin L Behar ◽  
Graeme F Mason ◽  
Henk M De Feyter ◽  
Douglas L Rothman ◽  
...  
Keyword(s):  
Ex Vivo ◽  
Metabolic Model ◽  
Synthesis Rate ◽  
Nmr Studies ◽  
Nmr Data ◽  
Glutamine Synthesis ◽  
Time Courses ◽  
Glutamine Uptake ◽  
C Nmr

13C Nuclear Magnetic Resonance (NMR) studies of rodent and human brain using [1-13C]/[1,6-13C2]glucose as labeled substrate have consistently found a lower enrichment (~25% to 30%) of glutamine-C4 compared with glutamate-C4 at isotopic steady state. The source of this isotope dilution has not been established experimentally but may potentially arise either from blood/brain exchange of glutamine or from metabolism of unlabeled substrates in astrocytes, where glutamine synthesis occurs. In this study, the contribution of the former was evaluated ex vivo using 1H-[13C]-NMR spectroscopy together with intravenous infusion of [U-13C5]glutamine for 3, 15, 30, and 60 minutes in mice. 13C labeling of brain glutamine was found to be saturated at plasma glutamine levels > 1.0 mmol/L. Fitting a blood–astrocyte–neuron metabolic model to the 13C enrichment time courses of glutamate and glutamine yielded the value of glutamine influx, VGln(in), 0.036 ± 0.002 μmol/g per minute for plasma glutamine of 1.8 mmol/L. For physiologic plasma glutamine level (~0.6 mmol/L), VGln(in) would be ~0.010 μmol/g per minute, which corresponds to ~6% of the glutamine synthesis rate and rises to ~11% for saturating blood glutamine concentrations. Thus, glutamine influx from blood contributes at most ~20% to the dilution of astroglial glutamine-C4 consistently seen in metabolic studies using [1-13C]glucose.

Diehloro(η5 -cyclopentadienyl)chrom-Dimer / Dichloro(η5-cyclopentadienyl)chromium Dimer

1983 ◽  
Vol 38 (11) ◽  
pp. 1406-1411 ◽  
Author(s):  
Frank H. Köhler ◽  
Ren de Cao ◽  
Klaus Ackermann ◽  
Josef Sedlmair
Keyword(s):  
Temperature Dependent ◽  
Nmr Studies ◽  
Magnetic Exchange ◽  
Chlorine Atoms ◽  
X Ray ◽  
Nmr Data ◽  
Metal Metal ◽  
C Nmr

Reaction of chromocene with chloroform yields [Cp2Cr]+[CpCrCl3]- (2) which is trans­formed to trans-[CpCrCl2]2 (3 a) on heating and to a mixture of cis/trans-[CpCrCl2]2 (3 b/a) on standing in chloroform. 2 and 3a/b have been characterized by paramagnetic 1H and 13C NMR yielding the first spectra of the chromocenium cation and the halfsandwich type [CpCrX2L]n-. For comparison, CpCrCl2(pyridine) (4) has been studied; the NMR data of 4 and [CpCrC3]- indicate that both are electronically similar. An X-ray analysis shows one isomer of 3 to be the trans-compound. Its chromium and bridging chlorine atoms consti­tute a square with a metal-metal distance of 336.2 pm. Magnetic exchange is established for 3 a by temperature dependent NMR studies. The X-ray results suggest superexchange to be the dominating mechanism.

Structural determination of the polysaccharide antigens of Neisseria meningitidis serogroups Y, W-135, and BO

1976 ◽  
Vol 54 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Apurba K. Bhattacharjee ◽  
Harold J. Jennings ◽  
C. Paul Kenny ◽  
Adèle Martin ◽  
Ian C. P. Smith
Keyword(s):  
Sialic Acid ◽  
Acetyl Derivative ◽  
Major Product ◽  
Hydroxyl Group ◽  
Nmr Studies ◽  
Acetylneuraminic Acid ◽  
Nmr Data ◽  
Polysaccharide Antigens ◽  
C Nmr

The purified high molecular weight serogoup Y meningococcal polysaccharide contains equimolar proportions of D-glucose and N-acetylneuraminic acid and is partially O-acetylated. Carbon-13 nuclear magnetic resonance (NMR) studies, together with other chemical data, have indicated that the polysaccharide is linked only at C-6 of the D-glucose and C-4 of the sialic acid residues, all the linkages being in the α-configuration. The 13C NMR data also indicated that the Y polysaccharide is composed of an alternating sequence of these two different residues, and this was confirmed by its autohydrolysis where the major product was 4-O-α-D-glucopyranosyl-β-D-N-acetylneuraminic acid. The W-135 polysaccharide differs from that of Y only in the absence of O-acetylation and in the configuration of one hydroxyl group of the disaccharide repeating unit. In this case autohydrolysis yielded 4-O-α-D-galactopyranosyl-β-D-N-acetylneuraminic acid as the major product. Structural evidence indicates that the BO and Y polysaccharides are identical.Methanolysis of the Y polysaccharide yielded in addition to the methyl glycosides of glucose and sialic acid, a 9-O-acetyl derivative of the latter. This derivative was formed during the re-N-acetylation process and its formation was mainly due to the presence of sodium ions in the original polysaccharide.

Magnitudes of 18O isotope shifts in 13C nuclear magnetic resonance spectra of ketones and alcohols

1980 ◽  
Vol 58 (13) ◽  
pp. 1311-1315 ◽  
Author(s):  
James Diakur ◽  
Thomas T. Nakashima ◽  
John C. Vederas
Keyword(s):  
Nmr Spectra ◽  
Negative Charge ◽  
Carbonyl Oxygen ◽  
Upfield Shift ◽  
Isotope Shifts ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
18O Isotope ◽  
Negative Charge Density ◽  
C Nmr

The magnitudes of 18O-induced isotope shifts in 13C nmr spectra of ketones and aldehydes are dependent on structure and range from about 0.05 ppm to 0.03 ppm for the carbon attached to 18O. An increase in negative charge density on the carbonyl oxygen or conjugation to an aromatic ring reduces the size of the upfield shift. The shifts in [18O]alcohols are solvent-dependent, range from 0.03 ppm to 0.01 ppm, and tend to decrease in the order tertiary ≥ secondary ≥ primary ≥ phenols.

13C-NMR-Untersuchiingen an einigen Organosilanen /13 C NMR Studies on Some Organosilanes

1979 ◽  
Vol 34 (9) ◽  
pp. 1270-1274 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Werner Biffar
Keyword(s):  
13C Nmr ◽  
Structural Features ◽  
Coupling Constants ◽  
Coupling Mechanism ◽  
Nmr Studies ◽  
Nmr Parameters ◽  
Nmr Data ◽  
Fermi Contact ◽  
Fermi Contact Term ◽  
C Nmr

Abstract13C-NMR data (δ13C, J(13C1H), J(13C13C), J(29Si13C)) of noncyclic organosilanes CH4-n[Si(CH3)3]n (n = 1-4), (CH3)4-nC[Si(CH3)3]n (n = 1, 3, 4) and cyclic organosilanes [(CH3)2SiCH2]n (n = 2, 3), (CH3)2Si(CH2)3 are reported. Comparison of reduced coupling constants 1K proves the Fermi-contact-term to be the dominant coupling mechanism. Structural features of the four-membered heterocycles become apparent by comparison of their 13C NMR parameters with those of corresponding cycloalkanes, noncyclic organo­silanes and the 1,3,5-trisilacyclohexane derivative.

13C- und 15N-NMR-spektroskopische Untersuchungen einiger Pentacarbonylchrom-Aminophosphan-Komplexe/13C and 15N NMR Spectroscopic Study of Some Pentacarbonylchromium-Aminophosphane Complexes

1989 ◽  
Vol 44 (1) ◽  
pp. 55-62 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Klaus Schamei ◽  
Max Herberhold
Keyword(s):  
Binuclear Complex ◽  
Nmr Spectra ◽  
15N Nmr ◽  
Amino Groups ◽  
Nmr Parameters ◽  
Nmr Data ◽  
Regular Change ◽  
Nuclear Shielding ◽  
The Relationship ◽  
C Nmr

13C and 15N NMR data are reported for the free aminophosphanes ʹBu3-nP(NH2)n (n = 1 (1), 2 (2)), for the corresponding pentacarbonylchromium complexes (OC)5Cr-P(ʹBu)3-n(NH2)n (n = 1 (3), n = 2 (4), n = 3 (5)), and for other (OC)5Cr-aminophosphane complexes such as (OC)5Cr-P(NMe2)3, (6 ) and a binuclear complex (7) in which the sulfurdiimide derivative ʹBu(NH2)P-NSN-P(NH2)ʹBu serves as the phosphane ligand. Various techniques (e.g. INEPT and reverse two-dimensional (2D) 1H {15N}-experiments) have been used for recarding the 15N NMR spectra at natural abundance. In contrast to suggestions in the literature, the relationship between the 13C NMR parameters for the axial and equatorial CO groups and the σ-donor/π-acceptor properties of the phosphane ligand is not straightforward. The 15N resonances of the (OC)5Cr complexes 3, 4, 6 are shifted to higher frequencies with respect to those of the free ligands, and there is a regular decrease in 15N nuclear shielding in the series of 3, 4, 5. The |1J(31P15N)| values vary between 17 and 65 Hz, the smaller values being observed for the (OC)5Cr complexes. The lack of a regular change in the magnitude of 1J(31P15N) in the series 3, 4, 5 indicates that this parameter is influenced by the nature of both the Cr-P and the P-N bonds as a function of the number of amino groups.

Sesquiterpenes and Flavonoid Aglycones from a Hungarian Taxon of the Achillea millefolium Group

2002 ◽  
Vol 57 (11-12) ◽  
pp. 976-982 ◽  
Author(s):  
Sabine Glasl ◽  
Pavel Mucaji ◽  
Ingrid Werner ◽  
Armin Presser ◽  
Johann Jurenitsch
Keyword(s):  
2D Nmr ◽  
The Other ◽  
Achillea Millefolium ◽  
Spectroscopic Methods ◽  
Nmr Studies ◽  
Flavonoid Aglycones ◽  
H Nmr ◽  
Nmr Data ◽  
First Time ◽  
C Nmr

The investigation of a dichloromethane extract of flower heads of a Hungarian taxon of the Achillea millefolium group led to the isolation of three flavonoid aglycones, one triterpene, one germacranolide and five guaianolides. Their structures were elucidated by UV-VIS, EI- and CI-MS, 1H NMR and 13C NMR spectroscopic methods as well as by 2D-NMR studies and by selective 1D-NOE experiments. Besides apigenin, luteolin and centaureidin, β-sitosterol, 3β-hydroxy-11α,13-dihydro-costunolide, desacetylmatricarin, leucodin, achillin, 8α-angeloxy-leucodin and 8α-angeloxy-achillin were isolated. Both latter substances are reported here for the first time. Their NMR data were compared with those of the other guaianolides. The stereochemistry of 3β-hydroxy-11α,13-dihydro-costunolide was discussed and compared with data of the literature.

The Action of Thrombin on Modified Fibrinogen

1983 ◽  
Vol 49 (03) ◽  
pp. 208-213
Author(s):  
A J Osbahr
Keyword(s):  
Physical Properties ◽  
Negative Charge ◽  
Lysine Residue ◽  
Fibrinopeptide A ◽  
Amino Groups ◽  
Lysine Residues ◽  
Citraconic Anhydride

SummaryThe modification of canine fibrinogen with citraconic anhydride modified the ε-amino groups of the fibrinogen and at the same time generated additional negative charges into the protein. The addition of thrombin to the modified fibrinogen did not induce polymerization; however, the fibrinopeptide was released at a faster rate than from the unmodified fibrinogen. The physical properties of the citraconylated fibrinogen were markedly altered by the modification of 50-60 lysine residues in one hour. A modified fibrinopeptide-A was released by thrombin from the modified fibrinogen and was electrophoretically more anionic than the unmodified fibrinopeptide-A. Edman analysis confirmed the modification of the lysine residue present in the peptide. The rate of removal of citraconylated fibrinopeptide-A from modified fibrinogen by thrombin was 30 to 40 percent greater than the cleavage of unmodified fibrinopeptide-A from unmodified fibrinogen. However, the modification of 60 or more lysine residues in the fibrinogen produced a decrease in the rate of cleavage of citraconylated fibrinopeptide-A. The results suggest that additional negative charge in the vicinity of the attachment of fibrinopeptide-A to canine fibrinogen aids in the removal of the peptide by thrombin.

Glucan isolated from leaves of Althaea officinalis L.

1983 ◽  
Vol 48 (7) ◽  
pp. 2082-2087 ◽  
Author(s):  
Alžbeta Kardošová ◽  
Jozef Rosík ◽  
Rudolf Toman ◽  
Peter Capek
Keyword(s):  
Medicinal Plant ◽  
Periodate Oxidation ◽  
Linear Structure ◽  
Water Soluble ◽  
Partial Hydrolysis ◽  
Methylation Analysis ◽  
Glycosidic Bonds ◽  
Nmr Data ◽  
Althaea Officinalis ◽  
C Nmr

A water-soluble low-molecular D-glucan was isolated from leaves of the medicinal plant marsh-mallow (Althaea officinalis L.). The results of methylation analysis, partial hydrolysis, periodate oxidation, and 13C NMR data indicated a virtually linear structure with α-(1→6) glycosidic bonds.

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