Search results for "magnetic resonance spectroscopy"
showing 10 items of 1362 documents
Installation of Amine Moieties into a Polycyclic Anodic Product Derived from 2,4-Dimethylphenol
2011
When 2,4-dimethylphenol is anodically treated, a dehydrotetramer with four contiguous stereocentres is readily obtained on a multi-gram scale. The substitution of a 2,4-dimethyl-phenoxy fragment by several amines was demonstrated, and the best results were obtained with primary amines. Optically pure α-chiral aliphatic amines yield diastereomeric mixtures that can be separated in most cases. The basic amine causes a partial hemiketal-opening of the bisbenzofuran moiety leading to an equilibrium within an α,β-unsaturated cyclohexenone. This dynamic behaviour occurs on the time scale of NMR spectroscopy and is also found by X-ray analysis providing a consistent picture.
5-Alkenyl-1,2,3-thiadiazole
1986
Es wird die Herstellung der Titelverbindungen 5 durch Bromierung-Dehydrobromierung entsprechender 5-Alkyl-1,2,3-thiadiazole 3, ihre spektroskopische Charakterisierung und ihre Umsetzung mit 4-Phenyl-4H-1,2,4-triazol-3,5-dion (6) zu 7, 8 beschrieben. 5-Alkenyl-1,2,3-thiadiazoles A method of preparation for the title compounds 5, by bromination-dehydrobromination of the corresponding 5-alkyl-1,2,3-thiadiazoles 3, their spectroscopical characterization, and the reaction of 5 with 4-phenyl-4H-1,2,4-triazole-3,5-dione (6) with formation of 7, 8 is described.
Determination of the Relative Stereochemistry of Flexible Organic Compounds by Ab Initio Methods: Conformational Analysis and Boltzmann-Averaged GIAO…
2002
Ab initio calculations at the Hartree-Fock level with full-geometry optimization using the 6-31G(d) basis set, and GIAO (gauge including atomic orbitals) 1 3 C NMR chemical shifts, are presented here as a support in the study of the stereochemistry of low-polar organic compounds having an openchain structure. Four linear stereoisomers, fragments of a natural product previously characterized by experimental 1 3 C NMR spectra, which possesses three stereogenic centers, 11 carbon atoms, and 38 atoms in total, were considered. Conformational searches, by empirical force-field molecular dynamics, pointed out the existence of 8-13 relevant conformers per stereoisomer. Thermochemical calculations …
Tautomerism and the Protonation/Deprotonation of Isocytosine in Liquid- and Solid-States Studied by NMR Spectroscopy and Theoretical Calculations
2011
Isocytosine crystallizes as a 1:1 ratio of two tautomers in a manner similar to that of the guanine and cytosine pairs in DNA. The solid-state NMR chemical shifts of crystalline neutral isocytosine, the sodium salt of isocytosine, and those of isocytosine hydrochloride were measured and related to the NMR parameters in aqueous and organic solutions. The experimental chemical shifts were compared with those calculated by three different methods: (1) calculations on isolated molecules, (2) calculations on isocytosine clusters of various sizes, and (3) infinite crystal calculations, that is, the gauge-including projector-augmented wave (GIPAW) method. The data obtained with the GIPAW method we…
1H,13C and17O NMR study of aromatic ring-substituted monochloro- and monobromo-(E)-3-phenylpropenals
1991
Trans-Cinnamaldehydes (CAs) or o-, m- and p-X-(E)-3-phenylpropenals; (X = Cl or Br) were synthesized and their 1H, 13C and 17O NMR spectra were measured, assigned and analysed. The long-range benzylic couplings are discussed in terms of the conformational characteristics of the related styrene systems. The 1H, 13C and 17O NMR substituent chemical shifts of the CA derivatives were compared with those of styrene and explained by the π-electron delocalization in the conjugated CCCO bond system of CA.
Antivirale Wirkstoffe, 27. Mitt. Die Aminomethinylierung von 5-Oxo-2-pyrazolin-3-carbonsäurederivaten
1986
Aus der mit s-Triazin (1) durchgefuhrten Aminomethinylierung der 5-Oxo-2-pyrazolin-3-carbonsaurederivate 2a,b gehen die 4-Aminomethylen-5-oxo-2-pyrazolin-3-carbonsaurederivat 4a,b und die C-Rubazonsauren 5a,b hervor. Bei 4a deuten die spektroskopischen Daten auf das Vorliegen der Z-Form (Abb. 1), fur 5a auf das der Z-s-cis-(OH)-Form (Abb. 2) hin. Die Strukturtypen 4 und 5 weisen Vertreter mit antiviraler, entzundungshemmender, temperatursenkender und antimykotischer Wirkung auf. Antiviral Agents, XXVII: Aminomethynylation of 5-Oxo-2-pyrazoline-3-carboxylic Acid Derivatives Aminomethynylation of the 5-oxo-2-pyrazoline-3-carboxylic acid derivatives 2a,b by means of s-triazine (1) yields the 4…
Syntheses, Structures and Reactivity of New Intramolecularly Coordinated Tin Alkoxides Based on an Enantiopure Ephedrine Derivative
2011
The syntheses of the tin compounds [LSn]2 (2), spiro-L2Sn (3), [LSnW(CO)5]2 (4), [LSnBr2]2 (5), spiro-L2Sn·SnBr4 (6) and LSn[OC(O)Ph]2 (8), where L = MeN(CH2CMe2O)[(S)-CH(Me)-(R)-CH(Ph)O], and (Ph4P)2SnBr6 (7) are reported. The compounds were characterized by elemental analysis, multinuclear NMR spectroscopy including 119Sn cross polarisation–magic angle spinning NMR (CP–MAS) (2, 3–6), electrospray ionization mass spectrometry (2–4) and single crystal X-ray diffraction analysis (2, 2·C7H8, 3a, 3b, 4·C7H8, 5, 6·C7H8, 7).
1H,13C and17O NMR study of substituted nitropyridines
1991
1H, 13C and 17O NMR spectra for 22 substituted nitropyridines were measured and their 1H NMR spectra were analysed. The most significant variations in the NMR parameters are found for isomeric hydroxy derivatives, owing to the possibility of keto–enol tautomerism. The prevalence of the keto form is observed in 2- and 4-hydroxy derivatives, while the 3-hydroxy derivative exists in its enol form. Among the three nuclei studied, 17O seems to be the best nucleus for probing the keto–enol tautomerism. No correlation is observed between the torsion angle of the nitro group and its 17O NMR chemical shift. Molecular mechanics calculations were performed to clarify the torsional energetics of the ni…
Protonation of 3-aminopyrroles
1987
Abstract The protonation of 3-aminopyrroles has been investigated using H and 13C n.m.r. spectroscopy. The spectral data are compatible with predominant protonation of the amino group with no evidence for protonation of the pyrrole ring.
An experimental and theoretical study of the isomerization of mononuclear bis(arylselenolato)bis(triphenylphosphine)platinum complexes [Pt(SeR)2(PPh3…
2003
Abstract Mononuclear bis(thienylselenolato)bis(triphenylphosphine)platinum [Pt(SeTh)2(PPh3)2] (Th=2-thienyl, C4H3S) has been prepared by the treatment of cis-[PtCl2(PPh3)2] with NaSeTh. The 31P-NMR spectroscopic information indicates that cis-[Pt(SeTh)2(PPh3)2] is initially formed in the reaction. Upon prolonged standing in solution it isomerizes to trans-[Pt(SeTh)2(PPh3)2]. The reaction of cis-[PtCl2(PPh3)2] with LiSeFu (Fu=2-furyl, C4H3O) affords immediately a mixture of cis- and trans-isomers of [Pt(SeFu)2(PPh3)2] with the relative amount of the trans-isomer increasing with time. The recrystallization of the two reaction mixtures yielded cis,anti- and trans,syn-isomers of [Pt(SeTh)2(PPh3…