Search results for "Chemical shift"
showing 10 items of 205 documents
Substituent effects on13C NMR parameters of chlorinated diphenyl ethers. A multiple linear regression analysis
1995
13C NMR chemical shifts and nJ(C,H) coupling constants of polychlorinated diphenyl ethers (PCDEs) were measured and analysed. The chlorine substituent effects on the chemical shifts and the coupling constants were determined by a multiple linear regression analysis. The 13C NMR chemical shifts depend on the conformational preferences in PCDEs. In addition to single substituent effects, corrective terms reflecting the conformational state of the molecule and the mutual steric interactions of two chlorine atoms had to be taken into account for the reliable prediction of the 13C chemical shifts. In contrast to chemical shifts, conformational effects play a minor role in the substituent effects…
Synthesis and NMR characterization of seven new substituted pyridine N-oxides
2008
Abstract Seven 3-substituted (alkylamino, alkylnitramino and alkylnitrosoamino) derivatives of pyridine N-oxide have been prepared and their 1H, 13C and 15N NMR chemical shifts assigned based on PFG 1H, 13C HMQC and PFG 1H, X (X = 13C or 15N) HMBC experiments. In the sterically most crowded congener, 3-ethylnitramino-4-nitropyridine N-oxide, chemical non-equivalence or diastereotopicity of the N–CH2 protons was observed probably due to the chirality of the adjacent amino nitrogen caused by its restricted inversion. The coalescence temperature for the 1H NMR chemical shifts of these geminal protons has been determined and the corresponding ΔG∗ for the energy barrier of the dynamic process ha…
13C and17O NMR study of methoxy groups in chlorinated Di- and trimethoxybenzenes
1990
13C and 17O NMR data [chemical shifts and 1J(CH) values] for the methoxy groups in isomeric 1,2-, 1,3- and 1,4-dimethoxybenzenes, 1,2,3-trimethoxybenzenes and most of their chlorinated derivatives and some related brominated compounds were measured for CDCl3 solutions. The 17O NMR chemical shifts show up to 60 ppm dispersion. Comparison between the compounds with and without adjacent chlorine atoms (2,6-di- and 2,4,6-tri-substitution) also showed a clear methoxy carbon chemical shift change. The number and position of the chlorine atoms in the aromatic ring give small but observable effects on the 17O NMR chemical shifts of the methoxy group if it is coplanar with the aromatic plane. Simila…
Association of 2-acylaminopyridines and benzoic acids. Steric and electronic substituent effect studied by XRD, solution and solid-state NMR and calc…
2013
Abstract Eight single crystal X-ray structures, solid-state NMR spectroscopic, and theoretical studies utilizing QTAIM methodology were used to characterize the 2-acyl (alkyl in acyl = methyl, ethyl, t-butyl, and 1-adamantyl) amino-6-R-pyridine/4-R′-benzoic acid (R,R′ = H or Me) cocrystals. As expected among alkyl groups 1-adamantyl due to its bulkiness has the most significant effect on the relative positions of molecules in cocrystals. In addition, the subtle electronic and steric effects by the methyl substituents were observed. The theoretical calculations with full geometry optimizations are in agreement with the experimental findings (geometry, energy of hydrogen bonds). Based on the …
ChemInform Abstract: Ortho-Substituent Effects in N-Arylacetamides. NMR and Molecular Mechanics Investigation.
2010
1H, 13C, 15N and 17O NMR spectra of N-phenylacetamide (acetanilide) and 21 ortho-substituted acetanilides were measured and assigned. The observed NMR parameters are related to the Hammett substituent parameters and conformational characteristics of the acetamido moiety estimated by molecular mechanics calculations. Significant relationships were found for the 13C NMR chemical shifts of C-5 (para to substituent) and the direct spin–spin coupling constant, 1J(C, H), of C-3 (ortho to substituent) with Hammett substituent parameters. For 15N NMR chemical shifts of the amido nitrogen, no general correlation with the Hammett substituent parameters was found. The interactions between functionalit…
The effect of some amines and alcohols on the organized structure of [bmim][BF4] investigated by 1H NMR spectroscopy
2008
The effect exerted by some amines and alcohols on the 1H NMR spectra of 1-butyl-3- methylimidazolium tetrafluoroborate [bmim][BF4] has been studied. This ionic liquid, which is one of the most widely used, is characterized by a high structural order degree, as a consequence of the symmetry and the coordination ability of the anion. In order to have information about the dependence of the detected effects on the alcohol or amine structure, some different primary, secondary and tertiary amines and alcohols have been considered. Furthermore, in the case of amines, their basicity has been also taken into account. Both amines and alcohols induce variation in chemical shifts values and signal mul…
Orthometalation of Tris(3-sodium sulfonatophenyl)phosphine with Dirhodium(II) Acetate
1998
Tetraacetatodirhodium(II) reacts with tris(3-sodium sulfonatophenyl)phosphine (TPPTS) giving [Rh2(μ-OOCCH3)3{μ-(3-NaO3SC6H3)P(C6H4SO3Na-3)2}(HOOCCH3)]·6H2O (1) and [Rh2(μ-OOCCH3)2{μ-(3-NaO3SC6H3)P(C6H4SO3Na-3)2}2(HOOCCH3)]·12H2O (2). Their structures and properties have been studied by electronic, IR, and 31P{1H}, 1H, 1H{31P}, and 13C{1H} NMR spectroscopies. In compound 1, one of the acetate bridges is replaced by a phosphine ligand, orthometalated via the C2 carbon atom of the phenyl ring. One axial site of the Rh24+ core is occupied by a sulfonato group of the metalated ring and another one by a labile molecule of acetic acid. 1H NMR spectroscopy shows that chemical shifts of the aromatic…
Predicting 19F NMR Chemical Shifts: A Combined Computational and Experimental Study of a Trypanosomal Oxidoreductase–Inhibitor Complex
2020
Abstract The absence of fluorine from most biomolecules renders it an excellent probe for NMR spectroscopy to monitor inhibitor–protein interactions. However, predicting the binding mode of a fluorinated ligand from a chemical shift (or vice versa) has been challenging due to the high electron density of the fluorine atom. Nonetheless, reliable 19F chemical‐shift predictions to deduce ligand‐binding modes hold great potential for in silico drug design. Herein, we present a systematic QM/MM study to predict the 19F NMR chemical shifts of a covalently bound fluorinated inhibitor to the essential oxidoreductase tryparedoxin (Tpx) from African trypanosomes, the causative agent of African sleepi…
Theoretical study of oligomeric alumatranes present in the chemistry of materials from micro to mesoporous molecular sieves and alumina composites
2008
Quantum chemical calculations using density functional theory have been carried out to investigate molecular precursors based on alumatranes which are one of the components with silatranes for the preparation of mesoporous aluminosilicate materials. In the same way, some oligomeric alumatranes of this study take part in chemical syntheses related to materials such as zeolites and alumina composite. Gas phase and solution equilibrium geometries of the alumatrane precursors were fully optimized at B3LYP level, modeling solvent effects using a self-consistent reaction field (SCRF). From these optimized geometries, calculations of the 1 H, 13 C and 27 Al NMR chemical shifts at GIAO/B3LYP/6-31G(…
Design, Construction, and Characterization of a New Regioisomer and Diastereomer Material Based on the Spirooxindole Scaffold Incorporating a Sulphon…
2020
The 1,3-dipolar cycloaddition reaction is one of the most rapid, and efficient protocols to access, and construct highly divergent heterocycle chiral auxiliaries. Free catalyst synthesis of spirooxindole scaffold incorporating sulphone moiety via one pot&ndash