Anisotropies in spin—spin coupling constants and chemical shifts as determined from the NMR spectra of molecules oriented by liquid crystal solvents

Lounila, Juhani; Jokisaari, Jukka

doi:10.1016/0079-6565(82)80004-6

Cited by 117 publications

(69 citation statements)

References 133 publications

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“…In addition, anisotropic contributions to the chemical shielding and the indirect spin-spin couplings, as well as quadrupolar couplings, in particular for deuterons, have been a rich source of information. [3][4][5][6][7][8][9] In addition to the properties of solutes, appreciable attention has been focused on the interaction mechanisms in the liquid state that determine the observed average degree of solute orientational order. In this context, the use of small, very well characterized probe molecules has been crucial.…”

Section: Introductionmentioning

confidence: 99%

Efficient analysis of highly complex nuclear magnetic resonance spectra of flexible solutes in ordered liquids by using molecular dynamics

Weber

Pizzirusso

Muccioli

et al. 2012

The Journal of Chemical Physics

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The NMR spectra of n-pentane as solute in the liquid crystal 5CB are measured at several temperatures in the nematic phase. Atomistic molecular dynamics simulations of this system are carried out to predict the dipolar couplings of the orientationally ordered pentane, and the spectra predicted from these simulations are compared with the NMR experimental ones. The simulation predictions provide an excellent starting point for analysis of the experimental NMR spectra using the covariance matrix adaptation evolutionary strategy. This shows both the power of atomistic simulations for aiding spectral analysis and the success of atomistic molecular dynamics in modeling these anisotropic systems.

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Section: Introductionmentioning

confidence: 99%

Efficient analysis of highly complex nuclear magnetic resonance spectra of flexible solutes in ordered liquids by using molecular dynamics

Weber

Pizzirusso

Muccioli

et al. 2012

The Journal of Chemical Physics

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“…The NMR spin Hamiltonian appropriate for spin-1 2 nuclei in molecules partially oriented in uniaxial LC solvents can be written in the high field approximation as (1) where B 0 is the magnetic field of the spectrometer (in the z direction of the laboratory-fixed frame), g i , I Ã i , and s i are the gyromagnetic ratio, dimensionless spin operator, and nuclear shielding (sum of the isotropic and anisotropic contributions), of nucleus i, respectively. The dipolar coupling D ij is defined as…”

Section: Theorymentioning

confidence: 99%

“…[3,4] For the H couplings the same has been known to hold for already a long time. [1] Recent LC NMR experiments and ab initio calculations indicate non-negligible contributions to 5 D exp FF and several types of D exp CF couplings in para-difluorobenzene. [5] An experimental study for the coupling anisotropy, D 1 J CF , in CH 3 F by applying solid-state NMR, gave only a coarse estimate for the quantity, because the information is masked by the broad lines of the spectrum.…”

Section: Introductionmentioning

confidence: 99%

“…[7,8] However, J aniso ij is likely to be bigger in couplings involving fluorine than in the proton couplings, due to more complicated electronic structure of the former. [1] At the same time, electronic structure calculations are significantly more demanding for fluorine-containing molecules than for simple hydrocarbons.…”

Section: Introductionmentioning

confidence: 99%

“…[1] As information on the molecular structure and orientation of the internuclear r ij vectors with respect to the magnetic field of the spectrometer is included in the D ij couplings, the J aniso ij contribution should be small or known, when accurate structural or orientational data are wanted. For example, the recently introduced method of obtaining the direct 13 C ± 13 C couplings at natural abundance for LC molecules using two-dimensional doublequantum experiments relies on the smallness of the J aniso ij contribution.…”

Section: Introductionmentioning

confidence: 99%

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Spin-Spin Coupling Tensors in Fluoromethanes

et al. 2000

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All spin-spin coupling tensors J of the fluoromethanes CH3F, CH2F2, and CHF3 are obtained theoretically by multiconfiguration self-consistent field linear response (MCSCF LR) ab initio calculations. Furthermore the principal values and the orientation of the principal axis systems of each theoretical J tensor are specified. Experimental liquid crystal NMR (LC NMR) data on the tensorial properties of the CF spin spin coupling in CH3F and CH2F2, and the FF spin-spin coupling in CHF3 are also reported. In the analysis of the experiments, the contributions from molecular vibrations, as well as that of the correlation of vibrational and rotational motion to the experimental anisotropic couplings, D(exp), are taken into account. The information of the anisotropic indirect coupling, 1/2J(aniso), is detected as the difference between D(exp) and the calculated dipolar coupling, D(calc). The extracted indirect contributions, 1/2J(aniso), are in fair agreement with the ab initio results. All relative (experimental and theoretical) CF and FF indirect contributions, 1/2J(aniso)/D(exp), are negative and under 1.7% in magnitude, when the observed molecular orientations are used. Therefore, in the one bond CF couplings and in the two bond FF couplings, the indirect contribution can normally be ignored without introducing serious error to the determination of molecular orientation and/or structure. However, a more accurate method is to partially correct for the indirect contribution by utilising the transferability of the spin-spin coupling tensors in related molecules. This is due to the fact that even small contributions may be significant, if the order parameter of the internuclear direction is negligibly small, leading to dominating indirect contributions. The very good agreement of the experimental values with the calculated coupling constants and the reasonable agreement in the anisotropic properties, which are experimentally much more difficult to define, indicates that the MCSCF LR method is capable of producing reliable J tensors for these systems, contrary to the case of density-functional theory.

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Cloppa RPA-AM1 analysis of the anisotropy of NMR1J(XY) coupling tensors in Me3XY compounds (X =13C,29Si,119Sn,207Pb; Y =19F,35Cl)

González¹,

Aucar²,

Azúa³

et al. 1997

Int. J. Quant. Chem.

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In this work, the CLOPPA approach is extended to allow the bond‐contribution analysis of the anisotropic part, ΔJ, of the indirect nuclear spin‐spin coupling tensor, J. As an example this method is applied to study the role played by the X‐Y bond, its antibonding orbital, and the Y lone pairs in determining the Fermi contact‐spin dipolar cross contribution to Δ1J(XY) in compounds of type Me3X(SINGLE BOND)Y (X = C, Si, Sn, Pb; Y = F, Cl). That contribution is found to be the main one, except for X = Pb, in this series of compounds. Calculations are carried out using semiempirical AM1 ground‐state wave functions. © 1997 John Wiley & Sons, Inc.

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Anisotropies in spin—spin coupling constants and chemical shifts as determined from the NMR spectra of molecules oriented by liquid crystal solvents

Cited by 117 publications

References 133 publications

Efficient analysis of highly complex nuclear magnetic resonance spectra of flexible solutes in ordered liquids by using molecular dynamics

Efficient analysis of highly complex nuclear magnetic resonance spectra of flexible solutes in ordered liquids by using molecular dynamics

Spin-Spin Coupling Tensors in Fluoromethanes

Cloppa RPA-AM1 analysis of the anisotropy of NMR1J(XY) coupling tensors in Me3XY compounds (X =13C,29Si,119Sn,207Pb; Y =19F,35Cl)

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