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Spin Coupling Constants (spin + coupling_constant)
Selected AbstractsA Theoretical Study of the NMR Spin,Spin Coupling Constants of the Complexes [(NC)5Pt,Tl(CN)n]n- (n = 0,3) and [(NC)5Pt,Tl,Pt(CN)5]3- : A Lesson on Environmental Effects.CHEMINFORM, Issue 2 2004Jochen Autschbach No abstract is available for this article. [source] Structural determination of ,-lactams by 1H and 13C NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2009Rubén Montalvo-González Abstract The thermodynamic products (,-lactams) of the degradation of ten different spirocyclic oxaziridines were analyzed by 1H and 13C NMR spectroscopy. The preferred conformations were determined by examining the homonuclear spin,spin coupling constant and the chemical shift effects of the N -substituent and the alkyl group of the aliphatic ring on 1H and 13C NMR spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] The Anomalous Deuterium Isotope Effect in the NMR Spectrum of Methane: An Analysis in Localized Molecular OrbitalsCHEMPHYSCHEM, Issue 9 2008Stephan P. A. Sauer Prof. Dr. Anomaly explained: The secondary isotope effect on the carbon,hydrogen indirect nuclear spin,spin coupling constant in methane, which is larger than the primary isotope effect, is explained in terms of contributions to the coupling constant from localized molecular orbitals. [source] Cyano-bridged Ln3+ -Cr3+ Binuclear Complexes [Ln(L)x(H2O)yCr(CN)6]·mL·nH2O (Ln=La,Nd, x=5, y=2, m=1 or 2, n=2 or 2.5; Ln=Sm,Dy, Er, x=4, y=3, m=0, n=1.5 or 2.0; L=2-pyrrolidinone): Structure, Magnetism and Spin Density MapCHINESE JOURNAL OF CHEMISTRY, Issue 3 2007Xian-Ru Sun Abstract In order to shed light upon the nature and mechanism of 4f-3d magnetic exchange interactions, a series of binuclear complexes of lanthanide(3+) and chromium(3+) with the general formula [Ln(L)5(H2O)2Cr(CN)6]·mL·nH2O (Ln=La (1), Ce (2), Pr (3), Nd (4); x=5, y=2, m=1 or 2, n=2 or 2.5; L=2-pyrrolidinone) and [Ln(L)4(H2O)3Cr(CN)6] ·nH2O (Ln=Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Er (10); x=4, y=3, m=0, n=1.5 or 2.0; L2-pyrrolidinone) were prepared and the X-ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln-CN-Cr unit, in which Ln3+ in a square antiprism environment is bridged to an octahedral coordinated Cr3+ ion through a cyano group. The magnetic properties of the complexes 3 and 6,10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g=1.98, J=0.40 cm,1, zJ,=,0.21 cm,1 on the basis of a binuclear spin system (SGd=7/2, SCr=3/2), revealing an intra-molecular Gd3+ -Cr3+ ferromagnetic interaction and an inter-molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory (DFT), combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm,1, supporting the observation of weak ferromagnetic intra-molecular interaction in 7. The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd3+ and Cr3+ was discussed. [source] Complete basis set prediction of methanol isotropic nuclear magnetic shieldings and indirect nuclear spin,spin coupling constants (SSCC) using polarization-consistent and XZP basis sets and B3LYP and BHandH density functionalsMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2009Teobald Kupka Abstract Efficient B3LYP and BHandH density functionals were used to estimate methanol's nuclear magnetic isotropic shieldings and spin,spin coupling constants in the basis set limit. Polarization-consistent pcS- n and pcJ- n (n = 0, 1, 2, 3 and 4), and segmented contracted XZP, where X = D, T, Q and 5, basis sets were used and the results fitted with simple mathematical formulas. The performance of the methods was assessed from comparison with experiment and higher level calculations. 1J(CH) and 3J(HH) values were determined from very diluted solutions in deuterochloroform and compared with theoretical predictions. The agreement between complete basis set (CBS) density functional theory (DFT) predicted isotropic shieldings and spin,spin values and experiment was good. The BHandH/pcS- n methanol shieldings obtained using structures optimized at the same level of theory are approaching the accuracy of the advanced coupled-cluster-singles-doubles-approximate triples (CCSD(T)) calculations. Copyright © 2009 John Wiley & Sons, Ltd. [source] Resolving an apparent discrepancy between theory and experiment: spin,spin coupling constants for FCCFMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2008Janet E. Del Bene Abstract Ab initio equation of motion coupled cluster singles and doubles (EOM,CCSD) and second-order polarization propagator approximation (SOPPA) calculations have been performed to evaluate spin,spin coupling constants for FCCF (difluoroethyne). The computed EOM-CCSD value of 3J(FF) obtained at the experimental geometry of this molecule supports the previously reported experimental value of 2.1 Hz, thereby resolving an apparent discrepancy between theory and experiment. This coupling constant exhibits a strong dependence on the CC and CF distances, and its small positive value results from a sensitive balance of paramagnetic spin-orbit (PSO) and spin-dipole (SD) terms. The three other unique FCCF coupling constants 1J(CC), 1J(CF), and 2J(CF) have also been reported and compared with experimental data. While 1J(CF) is in agreement with experiment, the computed value of 2J(CF) is larger than our estimate of the experimental coupling constant. Copyright © 2008 John Wiley & Sons, Ltd. [source] A review with comprehensive data on experimental indirect scalar NMR spin,spin coupling constants across hydrogen bondsMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2008Ibon Alkorta Abstract Scalar NMR spin,spin coupling constants across hydrogen bonds are fundamental in structural studies and as test grounds for theoretical calculations. Since they are scattered among many articles of different kinds, it seems useful to collect them in the most comprehensive way. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spin,spin coupling and substituent and halogen isotope shift effects in the fluorine NMR spectra of fluorinated cyclopropanes and cyclopropyl ethersMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007Wallace S. Brey Abstract The 19F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin,spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. Copyright © 2007 John Wiley & Sons, Ltd. [source] Long-range JCH heteronuclear coupling constants in cyclopentane derivatives.MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2007Part II Abstract Here we report the detailed measurement of long-range heteronuclear spin,spin coupling constants, especially 2, 3JCH spin,spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X -CPMG-HSQMBC and the 2D-coupled gHSQC {1H- 13C} experiment Copyright © 2006 John Wiley & Sons, Ltd. [source] Nonempirical calculations of NMR indirect spin,spin coupling constantsMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2006-unsaturated aldehydes, : Azomethines of the, Part 1 Abstract Configurational assignment of seven azomethines obtained from the ,-functionally substituted and nonsubstituted ,,,-unsaturated aldehydes has been performed on the basis of experimental measurements and the high-level ab initio calculations of their 1J(C,C) and 1J(C,H), involving the ,-imino carbon that demonstrated the marked stereochemical dependence of both coupling constants upon the orientation of the nitrogen lone pair in the diverse isomers of the title azomethines. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis and calculation of the 31P and 19F NMR spectra of hexafluorocyclotriphosphazeneMAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2005Libor Kapi Abstract The higher order high-resolution 31P and 19F NMR spectra of hexafluorocyclotriphosphazene (F2PN)3 were measured at 183 K and interpreted using subspectral analysis and iterative fitting computation. (F2PN)3 forms a rigid nine-spin system [A[X]2]3 with D3h symmetry. Two complete and very similar sets of six experimental spin,spin coupling constants, 1J(P,F), 2J(P,P), 2J(F,F), 3J(P,F), 4J(F,F)cis and 4J(F,F)trans, were determined for the first time. Theoretical DFT calculations of chemical shifts and coupling constants were performed to assess their predictive value. The PP/aug-cc-pVDZ treatment rendered the best agreement with experimental data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Non-empirical calculations of NMR indirect carbon,carbon coupling constants.MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2005Part 1, a practical guide to structural elucidation, saturated carbocycles: a reference data set Abstract Carbon,carbon spin,spin coupling constants, J(C,C), calculated at the SOPPA level for 50 mono-, bi- and polycycloalkanes in 10 previous papers are put in order and discussed on unified grounds. Basic structural trends of J(C,C) established in the original publications are summarized and briefly outlined for the representative series. Many unknown couplings are predicted with high reliability, and this provides a good reference data set and a practical guide to the structural elucidation of saturated carbocycles by means of J(C,C) coupling constants. Copyright © 2004 John Wiley & Sons, Ltd. [source] Non-empirical calculations of NMR indirect carbon,carbon coupling constants.MAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2004Monocycloalkanes, Part Abstract Carbon,carbon and carbon,hydrogen spin,spin coupling constants were calculated in the series of the first six monocycloalkanes using SOPPA and SOPPA(CCSD) methods, and very good agreement with the available experimental data was achieved, with the latter method showing slightly better results in most cases, at least in those involving calculations of J(C,C). Benchmark calculations of all possible 21 coupling constants J(C,C), J(C,H) and J(H,H) in chair cyclohexane revealed the importance of using the appropriate level of theory and adequate quality of the basis sets. Many unknown couplings in this series were predicted with high confidence and several interesting structural trends (hybridization effects, multipath coupling transmission mechanisms, hyperconjugative interactions) were elucidated and are discussed based on the present calculations of spin,spin couplings. Copyright © 2004 John Wiley & Sons, Ltd. [source] Indirect nuclear spin,spin coupling constants in 1,2-diboretane-3-ylidene, a homoaromatic system with , and , 3c/2e bonds.MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2004Comparison of experimental data with calculations using density functional theory (DFT) Abstract The non-classical 1,2-diboretane-3-ylidene 1a was studied by 13C and 29Si NMR spectroscopy in order to obtain coupling constants 1J(13C,11B) and 1J(29Si,13C). The magnitudes of 1J(13C,11B) were deduced from linewidth measurements in low-temperature 13C and 11B NMR spectra. Calculation of the coupling constants for model compounds related to 1a, using DFT methods based on optimized geometries [B3LYP/6,311+G(d,p)], gave data in agreement with the experiments. Furthermore, the calculations predict for the first time a negative sign of 1J(13C,11B) which mirrors the bonding situation in 1 as described by theory. Copyright © 2004 John Wiley & Sons, Ltd. [source] Predicted signs of reduced two-bond spin,spin coupling constants (2hKX,Y) across X,H,Y hydrogen bondsMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2004Janet E. Del Bene Abstract The reduced two-bond Fermi-contact terms and the reduced spin,spin coupling constants 2hKX,Y across X,H,Y hydrogen bonds for complexes stabilized by C,H,N, N,H,N, O,H,N, F,H,N, C,H,O, O,H,O, F,H,O and C,H,F hydrogen bonds are positive. The NMR Triplet Wavefunction Model (NMRTWM) indicates that the signs of the reduced FC terms and 2hKX,Y are determined by excited triplet states that have an odd number of nodes intersecting the X,Y axis between X and Y, thereby leading to an antiparallel alignment of the nuclear magnetic moments of atoms X and Y. Copyright © 2004 John Wiley & Sons, Ltd. [source] Interpreting 2hJ(F,N), 1hJ(H,N) and 1J(F,H) in the hydrogen-bonded FH,collidine complex,MAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2002Janet E. Del Bene Abstract Ab initio EOM-CCSD calculations were performed to determine 19F,1H, 19F,15N and 1H,15N spin,spin coupling constants in model complexes FH,NH3 and FH,pyridine as a function of the F,H and F,N distances. The absolute value of 1J(F,H) decreases and that of 1hJ(H,N) increases rapidly along the proton-transfer coordinate, even in the region of the proton-shared F,H,N hydrogen bond. In contrast, 2hJ(F,N) remains essentially constant in this region. These results are consistent with the recently reported experimental NMR spectra of FH,collidine which show that 1hJ(H,N) increases and 1J(F,H) decreases, while 2hJ(F,N) remains constant as the temperature of the solution decreases. They suggest that the FH,collidine complex is stabilized by a proton-shared hydrogen bond over the range of experimental temperatures investigated, being on the traditional side of quasi-symmetric at high temperatures, and on the ion-pair side at low temperatures. Copyright © 2002 John Wiley & Sons, Ltd. [source] A new approach to automated first-order multiplet analysisMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2002Sergey Golotvin Abstract The dependence of the values of NMR spin,spin coupling constants on molecular conformation can be a valuable tool in the structure determination process. The continuing increase in the resonance frequency of modern NMR spectrometers allows an increasing number of resonances to be examined using first-order multiplet analysis. While this can easily be done for the simplest patterns (doublets, triplets, quartets), more complex patterns can be extremely difficult to analyze. The task of deducing the coupling constant values from a multiplet is the reverse process of generating a conventional splitting tree from a single line (chemical shift) by sequential branching using a given set of coupling constants. We present a simple, straightforward method of deducing coupling constant values from first-order multiplets based on a general inverted splitting tree algorithm but also including a peak intensity normalization procedure that utilizes multiplet symmetry and generates a set of possible first-order intensity distribution patterns. When combined with an inverted splitting tree algorithm, it is possible to find an intensity pattern that allows the deduction of a proper set of coupling constants. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||