Search results for "Nmr data"
showing 10 items of 21 documents
Synthesis of 3-Oxa-guaianolides from Santonin
2000
Abstract This article reports on the transformation of santonin into two C10-epimeric 3-oxa-guaianolides which are 8-deoxyderivatives of several natural 3-oxaguaianolides isolated from Achillea species. The synthesis involved the photochemical rearrangement of the eudesmane skeleton into a guaiane skeleton and the transformation of the cyclopentane ring into a furan moiety with the concomitant loss of C3. Comparison of the NMR data of the synthetic products with those of the natural products confirms the β orientation of the hydroxyl group at C10 in the products isolated from Achillea.
Effects of substitutions on cyclopentadienyl rings in complexes with molybdenum-mercury bonds. 95Mo and 199Hg NMR studies
1995
NMR data for 95Mo and 199Hg nuclei have been obtained for new di- and trimetallic complexes Cp′(CO)3MoHgX containing molybdenum-mercury bonds and bulky and/or potentially bifunctional substituted cyclopentadienyl ligands; Cp′=C5HMe2Ph2, C5Me4Bz, C5Bz5, C5H4PPh2 and C5Me4PPh2 (Bz=CH2C6H5; Me =CH3; Ph=C6H5); X=Cp′(CO)3Mo, Cl, Br, 1, SCN. They are discussed within the context of our earlier results reported for analogous complexes with the cyclopentadienyl ligands bearing methyl groups. With the exception of phenyl substituted rings, a rather narrow range of 95Mo chemical shifts is found for the compounds with the same number of different substituents on cyclopentadienyl ligands. An outstandin…
Ab-initio crystal structure analysis and refinement approaches of oligo p-benzamides based on electron diffraction data.
2012
Ab-initio crystal structure analysis of organic materials from electron diffraction data is presented. The data were collected using the automated electron diffraction tomography (ADT) technique. The structure solution and refinement route is first validated on the basis of the known crystal structure of tri-p-benzamide. The same procedure is then applied to solve the previously unknown crystal structure of tetra-p-benzamide. In the crystal structure of tetra-p-benzamide, an unusual hydrogen-bonding scheme is realised; the hydrogen-bonding scheme is, however, in perfect agreement with solid-state NMR data.
15N NMR studies of tautomerism
2012
The literature related to 15N NMR studies of tautomerism is updated and discussed. The 15N NMR data show that the technique is applicable for both liquid and solid state (both crystalline and amorphous) materials. Modern computational methods combined with experimental NMR data can aid in the chemical shift assignments especially in case of crystalline materials (so-called NMR crystallography). This review article is divided into chapters based on the different classes of compounds and a brief description of experimental and computational NMR techniques is also included.
Phosphorescent Pt II Systems Featuring Both 2,2′‐Dipyridylamine and 1,3,5‐Triazapentadiene Ligands
2014
The treatment of cis-[Pt(dpa)(RCN)2][SO3CF3]2 {dpa = 2,2′-dipyridylamine, R = Me, Et, CH2Ph, Ph; [2a–d](OTf)2} (OTf = SO3CF3) with 2 equiv. of N,N′-diphenylguanidine [NH=C(NHPh)2] in CH2Cl2 solutions at room temp. for 16 h gives [Pt(dpa){NH=C(R)NC(NHPh)=NPh}][SO3CF3] {[3a,b,d](OTf)} as the addition products and [Pt(dpa){NH=C(R)NHC(R)=NH}][SO3CF3]2 {[4a,b](OTf)2} as the tailoring products. The formulation of complexes [3a,b,d](OTf) and [4a,b](OTf)2 was supported by satisfactory C, H, and N elemental analyses and agreeable high-resolution ESI-MS, IR, and 1H (including 1H–1H COSY experiments) and 13C{1H} NMR data. The structures of all of the platinum species were determined by single-crystal …
De Vries smectic A phase formed by a liquid crystal side chain copolymer? A13C NMR study
2005
We study the orientation and order parameter of a liquid crystalline random side chain copolymer by 13C NMR. Evidence has previously been presented that this material forms a de Vries smectic A phase. The NMR data show that the molecular tilt angle in the smectic A phase is very small or zero and the smectic A–smectic C* transition is attributed predominantly to a change of the molecular tilt rather than azimuthal ordering. We discuss the NMR results in the context of earlier X‐ray and elastic characterizations of structurally similar materials.
Stereoselective synthesis of the published structure of feigrisolide A. Structural revision of feigrisolides A and B.
2006
The total synthesis of the proposed structure of feigrisolide A is reported. Ethyl (S)-3-hydroxybutyrate was the chiral starting material. A Brown asymmetric allylation and an Evans aldol reaction were key steps of the synthesis. The NMR data of the synthetic product are different from those of the natural product. The published structure of feigrisolide A is therefore erroneous. A subsequent comparison of spectral data strongly suggests that feigrisolides A and B are identical with (-)-nonactic acid and (+)-homononactic acid, respectively.
Protein structure prediction assisted with sparse NMR data in CASP13
2019
CASP13 has investigated the impact of sparse NMR data on the accuracy of protein structure prediction. NOESY and 15 N-1 H residual dipolar coupling data, typical of that obtained for 15 N,13 C-enriched, perdeuterated proteins up to about 40 kDa, were simulated for 11 CASP13 targets ranging in size from 80 to 326 residues. For several targets, two prediction groups generated models that are more accurate than those produced using baseline methods. Real NMR data collected for a de novo designed protein were also provided to predictors, including one data set in which only backbone resonance assignments were available. Some NMR-assisted prediction groups also did very well with these data. CAS…
Validity of NMR pore-size analysis of cultutal heritage ancient building materials containing magnetic impurities
2007
NMR relaxation time distributions, obtained with laboratory and portable devices, are utilized to characterize the pore-size distributions of building materials coming from the Roman remains of the Greek-Roman Theatre of Taormina. To validate the interpretation of relaxation data in terms of pore-size distribution, comparison of results from standard and in situ NMR experiments with results of the mercury intrusion porosimetry (MIP) has been made. Although the pore-size distributions can be obtained by NMR in terms of either longitudinal (T-1) or transverse (T-2) relaxation times distributions, the shorter duration of the T-2 measurement makes it, in principle, preferable, although the dete…
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