Search results for "Chemical shift"
showing 10 items of 205 documents
1H, 13C and 15N NMR spectral characterization of twenty-seven 1,2-diaryl-(4E)-arylidene-2-imidazolin-5-ones.
2006
1H, 13C and 15N NMR chemical shifts and couplings nJ(H,C) in DMSO-d6 at 30 °C have been determined for 1,2-diaryl-(4E)-arylidene-2-imidazolin-5-one derivatives 1–27. Their chemical shift assignments are based on PFG DQF 1H,1H COSY, PFG 1H,13C HMQC as well as PFG 1H,13C and 1H,15N HMBC experiments. For compounds 1–10 including aryl fluorine substituent(s) also the couplings nJ(F,C) (n = 1 − 4) are reported. Copyright © 2006 John Wiley & Sons, Ltd.
Complete 1H and 13C NMR assignments of clerodane diterpenoids of Salvia splendens.
2006
Unambiguous and complete assignments of 1H and 13C NMR chemical shifts for five clerodane diterpenes, four of them isolated from Salvia splendens (salviarin, splendidin and splenolides A and B) and one obtained by acetylation of splenolide A, are presented. The assignments are based on 2D shift-correlated [1H,1H–COSY, 1H,13C-gHSQC–1J(C,H) and 1H,13C-gHMBC-nJ(C,H) (n = 2 and 3)] and nuclear Overhauser effect (NOE) experiments. The conformation of the rings of these compounds is supported by the 3J(H,H) values and NOE results. Copyright © 2006 John Wiley & Sons, Ltd.
Effect of electron-withdrawing substituents on the electrophilicity of carbonyl carbons
2005
Indexación: Scopus The substituent effects on the carbonyl carbon atom for a series of twelve substituted phenyl acetates have been rationalized using a global electrophilicity index. This index is linearly correlated with the experimental reaction rate coefficients. We found that, in contrast to the proposed interpretation based on experimental 13C NMR chemical shifts and ground state destabilization calculations, the electrophilicity of carbonyl compounds increases due to the effect promoted by electron-withdrawing groups in these systems. https://www.sciencedirect.com/science/article/pii/S0040402004018046?via%3Dihub
Über gemischte gruppe 14-gruppe 14-bindungen
1993
Abstract The lead-tin compounds o-Tol6PbSn, o-Tol3PbSnPh3 and Mes3PbSnPh3 have been synthesized from Li and halide precursors in THF/ether at low temperatures. The crystal structures of the S4 symmetric o-Tol4Pb and of the three isomorphous title compounds have been determined (d(SnSn) 2.883 (1), d (PbSn) 2.845 (2), d (PbPb) 2.895 (2), A). The long SnSn distance is in accordance with the Raman data for the pairs of p-Tol6/o-Tol6 substituents (ν(SnSn) 131/123, ν(PbSn) 114/114, ν(PbPb) 105/103 cm−1). The sequence of the 119Sn and 207Pb chemical shifts shows clearly a polarity Pbδ−Snδ+ for all lead-tin compounds investigated. The 1J (119Sn207Pb) and 1J(119Sn119Sn) couplings of identi…
Halogen effect on structure and 13 C NMR chemical shift of 3,6-disubstituted-N -alkyl carbazoles
2013
Structures of selected 3,6-dihalogeno-N-alkyl carbazole derivatives were calculated at the B3LYP/6-311++G(3df,2pd) level of theory, and their 13C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N-methyl and N-ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin–orbit zeroth-order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~−10 and ~−30 ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the haloge…
An ab initio study of the relation between NMR chemical shifts and solid-state structures: hexabenzocoronene derivatives
2000
The assignment of solid-state NMR spectra is studied by the use of model systems computed with ab initio methods. The investigated system is a hexabenzocoronene derivative, for which a T-like arrangement of dimer units is found in the solid-state structure. Here, a tetramer model is required to explain the intermolecular interactions influencing the spectrum, whereas a dimer model is found to be inadequate. For the tetramer model, agreement of the computed NMR spectrum with the experimental solid-state magic angle spinning MAS-NMR data is observed. This study implies that the combination of experimental NMR data with quantum chemical calculations can be employed as a useful tool in determin…
E-2-Benzylidenebenzocycloalkanones. IV. Studies on transmission of substituent effects on 13C NMR chemical shifts of E-2-(X-benzylidene)-1-tetralones…
2005
Abstract Single substituent parameter (SSP) and dual substituent parameter (DSP) analyses were applied to study the transmission of substituent effects on selected 13C NMR chemical shifts of the cyclic chalcone analogues, E-2-(4′-X-benzylidene)-1-tetralones (2) and E-2-(4′-X-benzylidene)-1-benzosuberones (3). In order to study how the geometry of the cyclic chalcone analogues affects the transmission of substituent effects similar investigations with the respective chalcones (4) were also performed. The results obtained earlier with the five-membered analogue E-2-(4′-X-benzylidene)-1-indanones (1) were also involved in the comparisons. Geometry optimization of the unsubstituted 1a, 2a, 3a a…
NMR chemical shift computations at second-order Møller-Plesset perturbation theory using gauge-including atomic orbitals and Cholesky-decomposed two-…
2021
We report on a formulation and implementation of a scheme to compute NMR shieldings at second-order Moller-Plesset (MP2) perturbation theory using gauge-including atomic orbitals (GIAOs) to ensure gauge-origin independence and Cholesky decomposition (CD) to handle unperturbed as well as perturbed two-electron integrals. We investigate the accuracy of the CD for the derivatives of the two-electron integrals with respect to an external magnetic field as well as for the computed NMR shieldings, before we illustrate the applicability of our CD based GIAO-MP2 scheme in calculations involving up to about one hundred atoms and more than one thousand basis functions.
Measuring molecular parity nonconservation using nuclear-magnetic-resonance spectroscopy
2017
The weak interaction does not conserve parity and therefore induces energy shifts in chiral enantiomers that should in principle be detectable in molecular spectra. Unfortunately, the magnitude of the expected shifts are small and in spectra of a mixture of enantiomers, the energy shifts are not resolvable. We propose a nuclear magnetic resonance (NMR) experiment in which we titrate the chirality (enantiomeric excess) of a solvent and measure the diasteriomeric splitting in the spectra of a chiral solute in order to search for an anomalous offset due to parity nonconservation (PNC). We present a proof-of-principle experiment in which we search for PNC in the \textsuperscript{13}C resonances…
13C NMR study on the methoxy carbon chemical shifts in chloro-substituted anisoles and guaiacols
1983
The 13C NMR chemical shifts of methoxy carbons in chlorinated anisoles and guaiacols have been measured for acetone-d6 solutions. Multiple linear regression analysis, and also ‘simple sum rule’ calculations, have been used to estimate the effects of the chlorine atoms (the position and degree of substitution) on the chemical shifts. The most important effects have shown to be due to the chlorine atoms adjacent to the methoxy and hydroxy substituents. For chlorinated guaiacols, the greatest effect is due to the chlorine atom adjacent to the methoxy group. For chlorinated anisoles, the substituents adjacent to the methoxy group (2,6-disubstitution) cause large effects. For both groups of comp…