Calculation Of Coupling Constants Research Articles

Vibronic coupling in cyclopentadienyl radical: A method for calculation of vibronic coupling constant and vibronic coupling density analysis

A method of calculation of vibronic or electron-phonon coupling constant is presented for a Jahn-Teller molecule, cyclopentadienyl radical. It is pointed out that symmetry breaking at degenerate point and violation of Hellmann-Feynman theorem occur in the calculations based on a single Slater determinant. In order to overcome these difficulties, the electronic wave functions are calculated using generalized restricted Hartree-Fock and complete active space self-consistent-field method and the couplings are computed as matrix elements of the electronic operator of the vibronic coupling. Our result agrees well with the experimental and theoretical values. A concept of vibronic coupling density is proposed in order to explain the order of magnitude of the coupling constant from view of the electronic and vibrational structures. It illustrates the local properties of the coupling and enables us to control the interaction. It could open a way to the engineering of vibronic interactions.

Nonempirical calculations of NMR indirect spin-spin coupling constants

Configurational assignment of seven azomethines obtained from the alpha-functionally substituted and nonsubstituted alpha,beta-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 alpha-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.

About the calculation of exchange coupling constants using density-functional theory: The role of the self-interaction error

The effect of the correction of the self-interaction error on the calculation of exchange coupling constants with methods based on density-functional theory has been tested in simple model systems. The inclusion of the self-interaction correction cancels the nondynamical correlation energy contributions simulated by the commonly used functionals. Hence, such correction should be important in the accurate determination of exchange coupling constants. We have also tested several recent functionals to calculate exchange coupling constants in transition-metal complexes, such as meta-GGA functionals or new formulations of hybrid functionals. The influence of the basis set and of the use of pseudopotentials on the calculated J values has also been evaluated for a Fe(III) dinuclear complex in which the paramagnetic centers bear several unpaired electrons.

DFT Study of HFI in Halogen-Containing Gold, Silver and Copper Complexes

We have analyzed the nuclear quadrupole coupling constants in copper, silver and gold halides and related compounds an the basis of the calculations with use of pseudo-potentials. The geometrical parameters and NQR halogen quadrupole constants obtained by these calculations substantially corresponded to the data of microwave spectroscopy in the gas phase. The analysis of the quality of the calculations with use of pseudo-potentials and the expanded basis set for the copper compounds was carried out. The ZORA model is shown to be a viable alternative to the computationally demanding B3LYP/SDD model for the calculation of halogen coupling constants in molecules. Besides the ZORA model as against BXYP/SDD model have been caused to realistic values of gold nuclear quadrupole coupling constants. In this case of the gold compounds the main contribution of the chemical Mossbauer shift comes from the 6s-orbiral population of the gold atoms.

Theoretical Isotropic Hyperfine Coupling Constants of Third-Row Nuclei (29Si, 31P, and 33S)

In a previous paper (Hermosilla, L.; Calle, P.; Garcia de la Vega, J. M.; Sieiro, C. J. Phys. Chem. A 2005, 109, 1114), an adequate computational protocol for the calculation of isotropic hyperfine coupling constants (hfcc's) was proposed. The main conclusion concerns the reliability of the scheme B3LYP/TZVP//B3LYP/6-31G* in the predictions of hfcc's with low computational cost. In the present study, we gain insight into the behavior of the above functional/basis set scheme on nuclei of the third row, for which few systematic studies have been carried out up to the present date. The systems studied are neutral, cationic, anionic, localized, and conjugated radicals, containing (29)Si, (31)P, and (33)S nuclei. After carrying out a regression analysis, we conclude that density functional theory (DFT) predictions on the hfcc's of the third-row nuclei are reliable for B3LYP/TZVP by using an optimized geometry with B3LYP/6-31G* combination. By comparison with other much more computationally demanding schemes, namely, B3LYP/cc-pVTZ and B3LYP/cc-pVQZ, we conclude that the B3LYP functional in conjunction with the TZVP basis set is the most useful computational protocol for the assignment of experimental hfcc's, not only for nuclei of first and second rows, but also for those of the third row.

Analysis of a cycloheptenone derivative: An experimental and theoretical approach

A detailed analysis with total assignment of 1H and 13C NMR spectral data for a cycloheptenone derivative, a key intermediate for the synthesis of perhydroazulene terpenoids, is related. These assignments are based on 1D 1H and 13C NMR and on 2D NMR techniques including gCOSY, gHSQC, gHMBC, J-resolved and NOEDIF experiments. The unequivocal assignments were supported by theoretical chemical shifts and scalar coupling constant calculations at GIAO B3LYP/cc-pVDZ level from optimized structures at the same level of theory.

Density functional theory study of indirect nuclear spin-spin coupling constants with spin-orbit corrections

This work outlines the calculation of indirect nuclear spin-spin coupling constants with spin-orbit corrections using density functional response theory. The nonrelativistic indirect nuclear spin-spin couplings are evaluated using the linear response method, whereas the relativistic spin-orbit corrections are computed using quadratic response theory. The formalism is applied to the homologous systems H2X (X=O,S,Se,Te) and XH4 (X=C,Si,Ge,Sn,Pb) to calculate the indirect nuclear spin-spin coupling constants between the protons. The results confirm that spin-orbit corrections are important for compounds of the H2X series, for which the electronic structure allows for an efficient coupling between the nuclei mediated by the spin-orbit interaction, whereas in the case of the XH4 series the opposite situation is encountered and the spin-orbit corrections are negligible for all compounds of this series. In addition we analyze the performance of the density functional theory in the calculations of nonrelativistic indirect nuclear spin-spin coupling constants.

Theoretical Study of the Magnetic Behavior of Ferric Wheels

Calculations of exchange coupling constants (J) based on density functional theory for eight complete, nonmodeled ferric wheels have been performed, and a comparison with the values obtained from magnetic susceptibility data is presented. The calculated J values obtained with a generalized-gradient approximation (GGA) functional are in good agreement with the experiment probably because the inclusion of pseudopotentials partially compensates the overestimation of the spin delocalization. The magnetostructural correlation obtained shows a strong dependence of the exchange coupling on both the Fe-O-Fe bond angle and the Fe-O bond distance. This correlation holds for both the ferric wheels and the alkoxo-bridged Fe(III) dinuclear complexes reported in the literature.

Multinuclear magnetic resonance studies of gaseous and liquid dimethyl ethers

Dimethyl ethers (DME): (CH 3) 2O, CH 3OCD 3, (CD 3) 2O have been studied using advanced NMR spectroscopy in liquid and gaseous states at 300 K. Extrapolation of the gas-phase results to the zero-density limit permitted the measurements of 1H, 13C and 17O nuclear magnetic shieldings of isolated DME molecules. The significance of intermolecular effects in the gaseous state as well as by coming from gas to liquid are also reported; measured gas-to-liquid shifts for 13C and 17O nuclei are negative (deshielding effects) but positive for 1H nuclei. The very weak linear dependence on density has also been observed for the carbon-proton and carbon-deuteron scalar coupling constants over one bond in the appropriate methyl group of DME. It was possible to obtain the coupling constants free from intermolecular interactions: 1 J 0(CH)=138.84 Hz in (CH 3) 2O, 1 J 0(CH)=138.81 Hz and 1 J 0(CD)=21.17 Hz in CH 3OCD 3 and 1 J 0(CD)=21.16 Hz in (CD 3) 2O. The magnitude of isotope effects on nuclear shieldings and indirect coupling constants caused by H/D substitution is also discussed. These new experimental results are suitable for a better verification of ab initio calculations of indirect coupling constants and nuclear magnetic shieldings of all nuclei in molecules under study.

Synthesis and Conformational Analysis of Saturated3,1,2‐Benzoxazaphosphinine 2‐Oxides

AbstractN‐Unsubstituted, N‐methyl and N‐benzyl cis‐ and trans‐2‐(hydroxymethyl)cyclohexylamines were subjected to ring closure with phenylphosphonic dichloride, phenyl dichlorophosphate and bis(2‐chloroethyl)phosphoramidic dichloride in order to synthesize P‐epimeric diastereomers of the corresponding unsubsituted and N‐substituted 2‐phenyl‐, 2‐phenoxy‐ and 2‐[bis(2‐chloroethyl)amino]octahydro‐2H‐3,1,2‐benzoxazaphosphinine 2‐oxides. The stereochemistry and conformations of the prepared compounds were analyzed mainly by variable‐temperature1H, 13C and 31P NMR spectroscopy. Geometry optimizations were performed for some trans‐fused molecules by utilizing the B3LYP DFT method and a locally dense basis set, followed by JH,P coupling constant calculations at the UB3LYP/cc‐pVTZ level of theory. The population of the N‐out conformation of the cis‐fused compounds was found to increase with increasing steric size of the N substituent (H < Me < CH2Ph), and also to be strongly influenced by the configuration at the phosphorus atom. The heteroring of the trans‐fused compounds predominantly adopts a chair conformation with the notable exception of the (2R*,4aS*,8aS*) epimers of the 2‐phenoxy‐substituted compounds, for which the axial tendency of OPh causes the heteroring to adopt mainly B2,4a‐ and/or 1S4a‐type nonchair conformations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Analysis and calculation of the 31P and 19F NMR spectra of hexafluorocyclotriphosphazene

The higher order high-resolution (31)P and (19)F NMR spectra of hexafluorocyclotriphosphazene (F(2)PN)(3) were measured at 183 K and interpreted using subspectral analysis and iterative fitting computation. (F(2)PN)(3) forms a rigid nine-spin system [A[X](2)](3) with D(3h) symmetry. Two complete and very similar sets of six experimental spin-spin coupling constants, (1)J(P,F), (2)J(P,P), (2)J(F,F), (3)J(P,F), (4)J(F,F)(cis) and (4)J(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.

1,3-Diaxial steric effects and intramolecular hydrogen bonding in the conformational equilibria of new cis-1,3-disubstituted cyclohexanes using low temperature NMR spectra and theoretical calculations

The conformational equilibria of 3-X-cyclohexanol [X = F ( 1), Cl ( 2), Br ( 3), I ( 4), Me ( 5), NMe 2 ( 6) and MeO ( 7)] and of 3-X-methoxycyclohexane [X = F ( 8), Cl ( 9), Br ( 10), I ( 11), Me ( 12), NMe 2 ( 13) and MeO ( 14)] cis isomers were determined from low temperature NMR spectra and PCMODEL calculated coupling constants. The energy differences between aa and ee conformers were obtained from these data ( Δ G J av and Δ G PC av , respectively) and also by the additivity principle from data for the monosubstituted cyclohexanes (Δ G Ad). H-1 and H-3 hydrogen vicinal coupling constants and Δ G J av values showed that the diequatorial conformer is predominant in the conformational equilibrium of the compounds studied at low temperature. However, Δ G PC av data show that compounds 6 and 7 constitute an exception, since they are almost equally populated by ee and aa at room temperature, due to stabilization of their aa conformer by an intramolecular hydrogen bond. Δ G Ad values, obtained according to the additivity principle, show a better agreement for compounds 2 and 3, since the 1,3-diaxial steric effect is counterbalanced by the formation of an intramolecular hydrogen bond (IAHB). For the remaining compounds, Δ G Ad values underestimate the energy differences, since the 1,3-diaxial steric effect, between X and OH or OCH 3, is absent in the monosubstituted compounds used as references. Moreover, the Δ G PC av , calculated from the coupling constants, obtained through the PCMODEL program, are rather smaller than the Δ G J av values, since the program does not have parameters for the effect, observed in this report, of a substituent at γ position on coupling constants values for the hydrogen under consideration.

A density functional study on magnetic exchange interaction between Mn(II) ion and nitronyl nitroxide radical in trans- and cis-metal-radical complexes

The magneto-structural correlation between a Mn(ll) ion, coordinated in an octahedral environment, and two nitronyl nitroxide radical ligands in trans- and cis-metal-radical complexes is investigated by the broken symmetry (BS) approach within density functional theory (DFT). The dependences of coupling constants J on three structural parameters: (i) bond angle θ (Mn-O-N (nitroxide)); (ii) rotating angle ψ, defined by the nitronyl nitroxide radical plane rotating around the axial Mn-O (nitroxide); (iii) bond distance R (Mn-O (nitroxide)) are directly calculated. Our calculations showed that both trans- and cis-Mn(ll)-radical complexes behave a stronger antiferromagnetic interaction, consistent with experiments. In view of molecular orbital theory, the direct exchanges, including σ-type and π-type exchanges, are responsible for the magnetic exchange pathways. There is a preferable linear correlation between the calculated coupling constants J and the overlap integral squares S b between the local magnetic orbitals at the various rotating angle ψ at the fixed bond angle θ and bond distance R, in both trans- and cis-Mn(ll)-radical complexes.

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 12—Aliphatic and alicyclic oximes

One-bond carbon-carbon coupling constants were calculated in a series of nine aliphatic and alicyclic oximes at the SOPPA (second-order polarization propagator approach) level in good agreement with the available experimental data, and several unknown couplings were predicted with high reliability. The experimental difference between J(C,C) of the corresponding carbon-carbon bonds in cis and trans orientations to the nitrogen lone pair is very well reproduced at the SOPPA level, and this provides an additional tool in the configurational assignment at the C=N bond in oximes and related systems.

Structure of the products of condensation of hydroxylamine with trifluoromethyl-β-diketones: assignments of the diastereotopic protons of the 4-methylene group in 5-hydroxy-5-trifluoromethyl-Δ2-isoxazolines

The combined use of 1H NMR spectroscopy with theoretical calculations of chemical shifts (GIAO) and coupling constants (B3LYP/6-311 ++G**) of a 5-hydroxy-5-trifluoromethyl-Delta2-isoxazoline has enabled solving the problem of the assignments of the diastereotopic protons in this compound. This result has been extended to 5-hydroxy-5-trifluoromethyl-Delta2-pyrazolines and the corresponding 5-trichloromethyl derivatives.

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 11?saturated carbocycles: a reference data set and a practical guide to structural elucidation

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.

Theoretical Rate Constants of Super-Exchange Hole Transfer and Thermally Induced Hopping in DNA

Recently, the electronic properties of DNA have been extensively studied, because its conductivity is important not only to the study of fundamental biological problems, but also in the development of molecular-sized electronics and biosensors. We have studied theoretically the reorganization energies, the activation energies, the electronic coupling matrix elements, and the rate constants of hole transfer in B-form double-helix DNA in water. To accommodate the effects of DNA nuclear motions, a subset of reaction coordinates for hole transfer was extracted from classical molecular dynamics (MD) trajectories of DNA in water and then used for ab initio quantum chemical calculations of electron coupling constants based on the generalized Mulliken-Hush model. A molecular mechanics (MM) method was used to determine the nuclear Franck-Condon factor. The rate constants for two types of mechanisms of hole transfer-the thermally induced hopping (TIH) and the super-exchange mechanisms-were determined based on Marcus theory. We found that the calculated matrix elements are strongly dependent on the conformations of the nucleobase pairs of hole-transferable DNA and extend over a wide range of values for the "rise" base-step parameter but cluster around a particular value for the "twist" parameter. The calculated activation energies are in good agreement with experimental results. Whereas the rate constant for the TIH mechanism is not dependent on the number of A-T nucleobase pairs that act as a bridge, the rate constant for the super-exchange process rapidly decreases when the length of the bridge increases. These characteristic trends in the calculated rate constants effectively reproduce those in the experimental data of Giese et al. [Nature 2001, 412, 318]. The calculated rate constants were also compared with the experimental results of Lewis et al. [Nature 2000, 406, 51].

Indirect Nuclear Spin-Spin Coupling Constants nJ(11B, 1H) and nJ(11B, 11B) in Some Boron Hydrides - Density Functional Theory (DFT) Calculations

Abstract Indirect nuclear spin-spin coupling constants J(11B,1H) and J(11B, 11B) in neutral and anionic boron hydrides 1- 17, calculated at the B3LYP/6-311+G(d,p) level of theory, are in good agreement with experimental data if available. This is shown for [BH4] − (1), B2H6 (2), B4H10 (3), B5H9 (4), or [B2H7]−(12). The calculations can be used to obtain values for those coupling constants for which experimental information is hardly accessible. This applies to complex spin systems involving the quadrupolar 11B nuclei such as in [B6H6]2− (11), to fast dynamic processes such as in B6H10 (5), [B5H8] − (10), [B6H7] − (11-H), [B3H8] − (13), Be(BH4)2 (14), (η5-C5H5)BeBH4 (15), Be(B3H8)2 (16), Me2AlB3H8 (17), or to instable species such as [B2H6]2− (6), B2H4 (7), B3H7 (8), and B4H8 (9). The experimental 11B NMR spectrum reported in the literature for the dianion 6does not resemble the spectrum predicted on the basis of the calculated coupling constants.

Two-Dimensional Pulsed EPR Studies of Vanadium-Exchanged ZSM-5

The pulsed electron paramagnetic resonance (EPR) technique of hyperfine sublevel correlation spectroscopy (HYSCORE) was used to obtain structural information about vanadium(VO2+)-exchanged ZSM-5. HYSCORE spectra were obtained for vanadium-exchanged ZSM-5 before and after dehydration and after the adsorption of ammonia. For the hydrated samples, proton hyperfine coupling constants were measured and assigned to equatorial water ligands with orientations perpendicular and parallel to the equatorial plane. Nitrogen hyperfine coupling constants for adsorbed ammonia were also determined from the HYSCORE spectra. The results were compared with previous density functional theory (DFT) calculations of hyperfine coupling constants for vanadyl model complexes.

The calculation of indirect nuclear spin-spin coupling constants in large molecules.

We present calculations of indirect nuclear spin-spin coupling constants in large molecular systems, performed using density functional theory. Such calculations, which have become possible because of the use of linear-scaling techniques in the evaluation of the Coulomb and exchange-correlation contributions to the electronic energy, allow us to study indirect spin-spin couplings in molecules of biological interest, without having to construct artificial model systems. In addition to presenting a statistical analysis of the large number of short-range coupling constants in large molecular systems, we analyse the asymptotic dependence of the indirect nuclear spin-spin coupling constants on the internuclear separation. In particular, we demonstrate that, in a sufficiently large one-electron basis set, the indirect spin-spin coupling constants become proportional to the inverse cube of the internuclear separation, even though the diamagnetic and paramagnetic spin-orbit contributions to the spin-spin coupling constants separately decay as the inverse square of this separation. By contrast, the triplet Fermi contact and spin-dipole contributions to the indirect spin-spin coupling constants decay exponentially and as the inverse cube of the internuclear separation, respectively. Thus, whereas short-range indirect spin-spin coupling constants are usually dominated by the Fermi contact contribution, long-range coupling constants are always dominated by the negative diamagnetic spin-orbit contribution and by the positive paramagnetic spin-orbit contribution, with small spin-dipole and negligible Fermi contact contributions.