Search results for "Carbon-13 NMR"
showing 10 items of 262 documents
Specificity of 15N NMR chemical shifts to the nature of substituents and tautomerism in substituted pyridine N-oxides
2012
1H, 13C, and 15N NMR chemical shifts have been measured for 2-aminopyridine N-oxide (1), its eleven derivatives (2–10, 13, 14), and 3-Cl and 3-Br substituted 4-nitropyridine N-oxides (11, 12). δ(15N) of pyridine ring nitrogen in 2-acetylaminopyridine N-oxides are 5.9–11.5 ppm deshielded from those in 2-aminopyridine N-oxides. When amino and acetylamino substituents are in 4-position, δ(15N) of ring nitrogen is 21.3 ppm deshielded in the acetylated derivative. The strong resonance interaction between 2-amino and 5-nitro groups reflects in the decrease of amino nitrogen shielding about 5.3–17.9 ppm. Also, 1H and 13C NMR spectral data are in agreement with 15N NMR results reflected as deshield…
Über antimon-haltige heterocyclen
1980
Abstract p -Nitrophenyl- and p -tolyl-oxadithia- and trithiastibocanes have been synthesized from the respective aryldichlorostibane and dithiole. The compounds have been characterised by means of 13 C NMR and vibrational spectra (ν(SBS 2 ) 350–320 cm −1 ). The crystal structure of p -nitrophenyltrithiastibocane has been determined ( R = 0.042). The eight-membered ring exhibits a boat-chair conformation. Single-bond distances of SbC and SbS (219, 244 and 245 pm), a 1,5-transannular Sb⋯S interaction (319 pm), and Sb⋯S and Sb⋯O (339 and 353 pm) intermolecular contacts, result in a six-coordinated Sb III (ψ-monocapped octahedral) species. The two additional Sb⋯S distances are in accordance w…
Über polygermane
1986
Abstract The optimum conditions for the synthesis of the trigermanes Ge3Ph8 and Ge3Me2Ph6 according to R2GeCl2 + 2 Ph3GeAk (Ak = Li, K) in HMPT have been determined. The main difficulty is to repress a nucleophilic attack of Ph3Ge− at newly formed GeGe bonds. The mass spectrum of Ge3Me2Ph6 shows rearrangements of the GePh3 and Ph/Me groups. The 13C NMR phenyl signals of di-, tri- and tetra-germanes are nearly identical. Ge3Ph8 and Ge4Ph10 transform to the plastically-crystalline state before melting (ΔH 45.3 and 54.9 kJ mol−1). The crystal structure of Ge3Me2Ph6 has been determined. The molecule has C2 symmetry (GeGe 242.9(1) pm, GeGeGe 120.3(1)°).
13C NMR spectra of eudesmane derivatives
1992
The 13C NMR spectral data of 18 eudesmane derivatives, mainly acids and esters of natural and synthetic origin, are reported, and the γ-effect of the epoxide ring in two diastereoisomeric epoxy esters is discussed.
Determination of octane numbers of gasoline compounds from their chemical structure by 13C NMR spectroscopy and neural networks
2001
Abstract A new theoretical model has been developed which explains the association between the molecular structure and the knock resistance of individual gasoline compounds convincingly. The constitutions of more than 300 individual gasoline components were correlated with their knock rating (Blending Research Octane Number, BRON) simultaneously. 13C NMR spectra of all compounds were binned in 28 chemical shift regions of different size. The number of individual carbon signals of the nearly 2500 carbons was counted in each shift region and was combined with the information about the presence or absence of the structure groups Oxygen, Rings, Aromatics, aliphatic Chains and oLefins (ORACL). T…
Long-range substituent and temperature effect on prototropic tautomerism in 2-(acylmethyl)quinolines
2001
Tautomeric equilibria between 2-(cinnamoylmethyl)quinoline, (Z)-1,2-dihydro-2-(cinnamoylmethylene)quinoline and (Z)-4-phenyl-1-(2-quinolyl)-1,3-butadien-2-ol were studied by 1H, 13C and 15N NMR methods. The —CHCH— fragment conjugated with phenyl and a strong electron donor p-(1-pyrrolidine) substituent were found to favour the enolimine tautomer. This undergoes fast exchange (on the NMR time-scale) with the enaminone form. The amount of the latter tautomer was found to increase at low temperatures. Copyright © 2001 John Wiley & Sons, Ltd.
Organometallic Complexes with Biological Molecules: VIII. Synthesis, Solid State andin vivo Investigation of Triorganotin(IV) Derivatives ofL-Homocys…
1997
Several new triorganotin(IV) derivatives of L-homocysteic acid (L-HCAH) with formula R3Sn(L-HCA) (R=Me, nBu, Ph) have been synthesized. Their solid-state configurations were determined by IR and Mossbauer spectroscopy. The tin(IV) atom is five-coordinated in all the complexes, with the L-homocysteic acid behaving as a monoanionic bidentate ligand coordinating the tin(IV) atom through a chelating or bridging carboxylate group. The sulfonate (SO3−) and NH3+ groups of L-homocysteic acid maintain their free acid configuration and hence do not participate to the coordination of the tin(IV) atom. Coordination hypotheses have been checked through the correlation between the Mossbauer parameter iso…
Diorganotin(IV)-2-mercaptopyrimidine complexes
1998
The complexes formed between the diorganotin(IV) moieties, R 2 Sn(IV), and the ligand 2-mercaptopyrimidine, (H)SPym, were investigated. Complexes R 2 SnHal(SPym) and R 2 Sn(SPym) 2 [R = Me, i Pr, n Bu, i Bu, t Bu, cyclohexyl(Cy), Ph] were synthesized, and characterized by elemental analysis. In the solid state, chelation of SPym through S and N donors was established by IR spectroscopy, and the nature of the environment of tin centers was investigated by 119 Sn Mossbauer spectroscopy. From the dynamics of 119 Sn nuclei determined by variable-temperature measurements on representative compounds [Me 2 SnCl(SPym) and Cy 2- SnBr(SPym)], as well as by point-charge model treatment of nuclear quad…
Tetra-p-tolyl-verbindungen p-Tol4Si und p-Tol4Ge: Ein beitrag zur konfiguration der tetraaryl-methan-analoga Ar4M (M = C, Si, Ge, Sn, Pb)
1992
Abstract p-Tol4Si and p-Tol4Ge have been obtained from the reaction of p-TolLi with SiCl4 and of p-TolMgBr with GeCl4, respectively. The crystal structures have been determined and compared with those of the homologous compounds p-Tol4Sn and p-Tol4Pb. The latter two molecules (space group I 4 ) exhibit a S4 axis running between the aromatic groups and are shortened along this axis: all four p-Tol groups are closer together than in an undistorted tetrahedron. In the cases of the silane and germane (space group Pc), the tetrahedron is lengthened along one of the bond axes CM: only three of the four p-Tol groups are closer together, and the set up of a special molecular symmetry is blocked. A…
Structural studies of acyl esters of entacapone
2001
Abstract The crystal structures of entacapone [(E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)propenamide] and three of its acyl esters were solved. Entacapone, and its monopivaloate and diacetate derivatives, exist in the E-form while its dibenzoate derivative adopts the Z-form in the crystalline state. The ethyl substituents of the E-form are not freely rotating, as demonstrated by the broad signals in the 1H and 13C NMR spectra. The rotation barrier for the E-form was defined by the crystal structures, which show that free rotation of the ethyl substituents is blocked by the cyano-group.