Search results for "Chemical shift"

Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in ter…

1998

Abstract 44 members of thecompound series Ph4−nMRn (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph3Sn (o-Tol) and PhSn (o-Tol)3 were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. 29 Si-, 119 Sn- and 207 Pb-NMR chemical shifts were determined in solution and in the solid state.73 Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by…

Über gemischte gruppe 14-gruppe 14-bindungen

1993

Abstract The six title compounds have been synthesized from Li/KSi/GePh 3 and chloride precursors in THF, DME or diethyl ether at low temperature. The six compounds crystallize isomorphously in the space group Pbca with ordered arrangement for the four symmetrical cases (SiSi 2.394, SiGe 2.412, GeGe 2.440 A) and statistical alignment for the two asymmetrical chains; angle range 116.5–123.3°. Replacement of Si by Ge atoms leads to low field NMR chemical shifts for 13 C ipso atoms and for directly bonded 29 Si atoms. This is in accordance with an enhanced electronegativity of germanium in comparison with silicon. UV/Vis and IR/Raman data are given.

ChemInform Abstract: Electron-Correlated Approaches for the Calculation of NMR Chemical Shifts

2010

1H NMR-spektroskopische Untersuchungen zur Strukturaufklärung von Oligo(hydroxy-5-nitro-1,3-phenylen)methylen Verbindungen

1976

Die 1H NMR-Spektren von 51 Oligo(hydroxy-5-nitro-1,3-phenylen)methylen Verbindungen (17 Zwei-, 18 Drei-, 14 Vier- und 2 Funfkernverbindungen) wurden in Pyridin als Losungsmittel aufgenommen. Bei Verbindungen mit ortho-Nitrophenolbausteinen zeigten die Signale fur die Protonen der Methyl- bzw. Methylengruppen in allen Fallen charakteristische chemische Verschiebungen δ, so das eine eindeutige Unterscheidung zwischen Methylgruppen in para- (δ=2,09−2,15 p.p.m.) und ortho-Stellung (δ=2,22−2,28 p.p.m.) zur phenolischen Hydroxyl-Gruppe, sowie zwischen para-para- (δ=3,77−3,97 p.p.m.), ortho-para- (δ=4,02−4,12 p.p.m.) und ortho-ortho-Methylenbrucken (δ=4,21−4,32 p.p.m.) moglich war. Bei Verbindunge…

Multinuclear magnetic resonance and x-ray diffraction studies of aminonitropyridines

1992

The 15N NMR spectra for 21 aminonitropyridines were measured and their chemical shifts assigned. The 1H and 13C NMR chemical shifts and spin–spin coupling constants were also determined for 16 compounds of this series. In order to relate the structural properties of nitramino groups and their 15N NMR chemical shifts in 2- and 4-nitramino-3-nitropyridines, which differ remarkably from all other amino groups studied, low-temperature 1H NMR, 17O NMR, comparative INEPT and IR spectroscopic studies were carried out. In addition, the x-ray crystal structure of 2-nitramino-3-nitropyridine was determined. Comparative spectroscopic studies showed that the nitramino derivatives exhibit different char…

1H,13C and15N NMR spectroscopic, x-ray structural andab initio/HF studies on nitramino andN-alkylamino-4-nitro derivatives of pyridineN-oxides and py…

2003

The 1H, 13C and 15N NMR spectra in DMSO-d6 were measured for eight nitraminopyridine N-oxides, ten 4-nitropyridine N-oxides, four 2-nitraminopyridines and five 4-nitropyridines. Their chemical shift assignments are based on PFG 1H,X (X = 13C and 15N) HMQC and HMBC experiments. The relative energies for the tautomers of two nitraminopyridine N-oxides were determined by ab initio HF/6–311G** calculations. A single-crystal x-ray structural analysis was made for 4-methyl-2-nitraminopyridine: C6H7O2N3, M = 153.15, triclinic, space group P-1 (No. 2), a = 7.0275(4), b = 6.8034(3), c = 8.6086(5) A, α = 103.620(2), β = 90.309(2), γ = 122.215(3)°, V = 334.11(3) A3, Z = 2. Copyright © 2003 John Wiley …

Über polygermane

1984

Abstract The optimum conditions for selectively cleaving off two phenyl groups in Ge2Ph6 by trichloroacetic acid have been determined. Neither trihaloacetic acids nor HCl/AlCl3 nor reactive tetrahalides MCl4 are suitable reagents for cleaving one phenyl group alone. The 13C NMR chemical shifts of functional phenyl-mono- and -digermanes are given. The crystal structure of 1,2-bis(trichloroacetate)tetraphenyldigermane has been determined and refined to R = 0.048. The digermane bond is bridged by both acetates (distances GeGe 239.3(2), GeO 207.3(3) and 231.4(3) pm). The Ge atoms have trigonal bipyramidal coordination.

13C and15N NMR chemical shift assignments ofN-1-(2- azidoethyl)-4-R-pyrimidin-2-ones by1H,X HMQ(B)C withz-gradient selection

1998

13C and 15N NMR chemical shift assignments based on z-gradient selected 1H,X (X=13C and 15N) HMQC and HMBC experiments are reported for N-1-(2-azidoethyl)pyrimidin-2-one (ring system of cytosine), its five 4-R derivatives [where R=NH2, OCH3, N(CH2)4, NHCH2CH(CH3)2 and N(CH3)2] and 2-azidoethyl tosylate. The possibilities of detecting all nitrogens in these molecules containing (i) an azido group at N-1 and (ii) an electronegative substituent at C-4 are limited. First, the terminal nitrogen of the azido group is difficult to observe because the nearest proton (in a CH2 group) is located four bonds away from it. Second, in contrast to N-1, N-3 in N-1-(2-azido-ethyl)-4-pyrimidin-2-ones remaine…

Nitramino, NRNO2 (R = H, CH3), as a substituent.13C and15N NMR spectroscopic study of nitraminobenzenes and -pyridines

1993

In order to clarify the special properties of the aryl-bound nitramino substituent NRNO 2 (R=H, CH 3 ), 13 C and 15 N NMR spectra of six nitraminobenzenes and nine nitraminopyridines were measured in DMSO-d 6 and their chemical shifts assigned. 1 H NMr chemical shifts and spin-spin coupling constants of all the compounds were also determined. In contrast to the behaviour of nitropyridines or -benzenes studied previously, most of the present compounds gave very broad 17 O NMR lines even at elevated temperatures and their 17 O NMR data were not useful for any reliable conclusions

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…