Search results for "Spectroscopy"
showing 10 items of 10293 documents
Surface composition analysis during the oxidation of ferrites: A necessity
1998
The cationic composition of a titanium ferrite (Fe 2.5 Ti 0.5 O 4 ) has been followed by XPS during its oxidation in cation deficient phases (without crystallographic transformation) in order to reveal a dynamic segregation phenomenon. Indeed, during this oxidation, an important modification of the chemical composition of the first layers of the material has been revealed: below 350 °C, the titanium ferrites surface becomes richer in iron and poorer in titanium. But, if the reaction is extended above 400 °C, some titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are present in the material. Finally,…
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.
Synthesis, Crystal Structure, and Properties of Multicomponent Bis(ethylenedithio)tetrathiafulvalene Charge-Transfer Salts of the [Mo3S7Br6]2- Cluster
2005
A new family of bis(ethylenedithio)tetrathiafulvalene (ET) radical salts has been prepared in the presence of a triangular molybdenum sulfide cluster of formula [Mo 3 S 7 Br 6 ] 2 - , which contains highly electrophilic axialsulfur atoms. A systematic change in the experimental conditions yields five different salts, namely (ETA)2(ET B )[Mo 3 S 7 Br 6 ] 2 . CH 2 Br 2 (1), (ETA)(ET B )Mo 3 S 7 Br 6 ].1.1CH 2 Br 2 (2), (ETA)(ETB)(ET C ){[Mo 3 S 7 Br 6 ]Br}.0.5C 2 H 4 Cl 2 (3), (ET)((n-Bu 4 )N)-[Mo 3 S 7 Br 6 ] (4), and (ET)(Ph4P)[Mo 3 S 7 Br 6 ].0.5CH 3 CN (5), where the ET subscript denotes crystallographically independent molecules. The five compounds have been structurally characterized, a…
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…
Organotin(IV) chloride complexes with phosphocholine and dimyristoyl-L-?-phosphatidylcholine
2000
Several complexes of R n SnCl 4-n (R = Me, Ph, n = 1-3; R = nBu, n = 2, 3) with phosphocholine and dimyristoyl-L-α-phosphatidylcholine (phospholipid) have been synthesized and characterized by means of Mossbauer spectroscopy and NMR. Triorganotin chlorides form complexes of (R 3 SnCl) 2 .L stoichiometry with a trigonal bipyramidal pentacoordinate tin environment, while the others form 1:1 complexes with an octahedral hexacoordinate tin environment, with the ligands coordinating through anionic phosphodiester moieties in all cases.
Synthesis, structural analysis, and thermal and spectroscopic studies of methylmalonate-containing zinc(II) complexes
2012
The synthesis, crystal structure, thermal analysis and spectroscopic studies of five zinc(II) complexes of formulae [Zn(Memal)(H2O)]n (1) and [Zn2(L)(Memal)2(H2O)2]n (2-5) [H2Memal = methylmalonic acid, and L = 4,4′-bipyridine (4,4′-bpy) (2), 1,2-bis(4-pyridyl)ethylene (bpe) (3), 1,2-bis(4-pyridyl)ethane (bpa) (4) and 4,4′-azobispyridine (azpy) (5)] are presented here. The crystal structure of 1 is a three-dimensional arrangement of zinc(II) cations interconnected by methylmalonate groups adopting the μ3-κ2O:κO’:κO”:κO”’ coordination mode to afford a rare (10,3)-d utp-network. The structures of the compounds 2-5 are also three-dimensional and they consist of corrugated square layers of meth…