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Int. J. Mol. Sci., Volume 4, Issue 3 (March 2003), Pages 62-157

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Editorial

Jump to: Research

Open AccessEditorial Special Issue on Nuclear Magnetic Resonance Spin–Spin Coupling Constants — Calculations and Measurements
Int. J. Mol. Sci. 2003, 4(3), 62-63; doi:10.3390/i4030062
Received: 12 February 2003 / Published: 25 February 2003
Cited by 1 | PDF Full-text (16 KB) | HTML Full-text | XML Full-text

Research

Jump to: Editorial

Open AccessArticle Review on DFT and ab initio Calculations of Scalar Coupling Constants
Int. J. Mol. Sci. 2003, 4(3), 64-92; doi:10.3390/i4030064
Received: 24 May 2002 / Accepted: 17 July 2002 / Published: 25 February 2003
Cited by 33 | PDF Full-text (213 KB) | HTML Full-text | XML Full-text
Abstract The present review summarizes the information available on the ab initio calculations of spin-spin nuclear coupling constants through hydrogen bonds or in van der Waals complexes. It also reports the sources of experimental data on nhJXY scalar couplings. Full article
Open AccessArticle Solvent Effects on Nuclear Magnetic Resonance 2J(C,Hf) and 1J(C,Hf) Spin–Spin Coupling Constants in Acetaldehyde
Int. J. Mol. Sci. 2003, 4(3), 93-106; doi:10.3390/i4030093
Received: 1 July 2002 / Accepted: 22 August 2002 / Published: 25 February 2003
Cited by 12 | PDF Full-text (202 KB) | HTML Full-text | XML Full-text
Abstract
The known solvent dependence of 1J(Cc,Hf) and 2J(C1,Hf) couplings in acetaldehyde is studied from a theoretical viewpoint based on the density functional theory approach where the dielectric solvent effect is taken into account
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The known solvent dependence of 1J(Cc,Hf) and 2J(C1,Hf) couplings in acetaldehyde is studied from a theoretical viewpoint based on the density functional theory approach where the dielectric solvent effect is taken into account with the polarizable continuum model. The four terms of scalar couplings, Fermi contact, paramagnetic spin orbital, diamagnetic spin orbital and spin dipolar, are calculated but the solvent effect analysis is restricted to the first term since for both couplings it is by far the dominant contribution. Experimental trends of Δ1J(Cc,Hf) and Δ2J(C1,Hf) Vs ε (the solvent dielectric constant) are correctly reproduced although they are somewhat underestimated. Specific interactions between solute and solvent molecules are studied for dimethylsulfoxide, DMSO, solutions considering two different one-to-one molecular complexes between acetaldehyde and DMSO. They are determined by interactions of type C=O---H---C and S=O---H---C, and the effects of such interactions on 1J(Cc,Hf) and 2J(C1,Hf) couplings are analyzed. Even though only in a semiquantitative way, it is shown that the effect of such interactions on the solvent effects, of Δ1J(Cc,Hf) and Δ2J(C1,Hf), tend to improve the agreement between calculated and experimental values. These results seem to indicate that a continuum dielectric model has not enough flexibility for describing quantitatively solvent effects on spin-spin couplings. Apparently, even for relatively weak hydrogen bonding, the contribution from “direct” interactions is of the same order of magnitude as the “dielectric” effect. Full article
Open AccessArticle Experimental Determination of Pseudorotation Potentials for Disubstituted Cyclopentanes Based on Spin–Spin Coupling Constants
Int. J. Mol. Sci. 2003, 4(3), 107-118; doi:10.3390/i4030107
Received: 5 August 2002 / Accepted: 5 November 2002 / Published: 25 February 2003
Cited by 5 | PDF Full-text (417 KB) | HTML Full-text | XML Full-text
Abstract
Complete analysis of 1H-NMR spectra of trans-1,2-dichlorocyclopentane and trans-1,2-dibromocyclopentane was performed with use of our total lineshape fitting algorithm VALISA. The resulting high precision spin-spin coupling constants were then applied to the problem of conformational analysis, yielding a continuos potential of pseudorotation
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Complete analysis of 1H-NMR spectra of trans-1,2-dichlorocyclopentane and trans-1,2-dibromocyclopentane was performed with use of our total lineshape fitting algorithm VALISA. The resulting high precision spin-spin coupling constants were then applied to the problem of conformational analysis, yielding a continuos potential of pseudorotation for the studied compounds in CDCl3, CCl4, and CD3CN solutions. Full article
Open AccessArticle Solvent Effects on the Indirect Spin–Spin Coupling Constants of Benzene: The DFT-PCM Approach
Int. J. Mol. Sci. 2003, 4(3), 119-134; doi:10.3390/i4030119
Received: 1 September 2002 / Accepted: 15 November 2002 / Published: 25 February 2003
Cited by 26 | PDF Full-text (121 KB)
Abstract
We present an extension of the Polarizable Continuum Model (PCM) to the calculation of solvent effects on indirect spin–spin coupling constants for Hartree–Fock wave functions and Density Functional Theory. This is achieved by implementing the PCM model for singlet and triplet linear response
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We present an extension of the Polarizable Continuum Model (PCM) to the calculation of solvent effects on indirect spin–spin coupling constants for Hartree–Fock wave functions and Density Functional Theory. This is achieved by implementing the PCM model for singlet and triplet linear response functions. The new code is used for calculating the solvent effects on the indirect spin–spin coupling constants of benzene. For the 1J(H13C) coupling constants, our calculated solvent shifts are in good agreement with experimental observations when geometry relaxation is taken into account. However, our results do not support the extrapolated gas-phase value for this coupling constant. A new experimentally derived 1J(H 13C) for a vibrating benzene molecule at 300 K is proposed. Full article
Open AccessArticle Gas–Phase Studies of Spin–Spin Coupling Constants
Int. J. Mol. Sci. 2003, 4(3), 135-142; doi:10.3390/i4030135
Received: 30 August 2002 / Accepted: 4 November 2002 / Published: 25 February 2003
Cited by 18 | PDF Full-text (62 KB) | HTML Full-text | XML Full-text
Abstract
Recent results of experimental spin-spin coupling constants are reviewed and their relation to ab initio calculations is discussed. It is shown that the NMR measurements of spin-spin coupling are density dependent in the gas phase. The extrapolation to the zerodensity limit is required
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Recent results of experimental spin-spin coupling constants are reviewed and their relation to ab initio calculations is discussed. It is shown that the NMR measurements of spin-spin coupling are density dependent in the gas phase. The extrapolation to the zerodensity limit is required in order to obtain the Jo coupling constants which are free from intermolecular interactions. Such coupling constants can be used as the experimental standards for any comparison with the results of appropriate calculations. It is also pointed out that the effects of the rotational and vibrational motion of nuclei in a molecule can be estimated completely only by theoretical methods. Full article
Open AccessArticle The Spin–Spin Coupling Constants in Ethane, Methanol and Methylamine: A Comparison of DFT, MCSCF and CCSD Results
Int. J. Mol. Sci. 2003, 4(3), 143-157; doi:10.3390/i4030143
Received: 12 September 2002 / Accepted: 10 December 2002 / Published: 25 February 2003
Cited by 23 | PDF Full-text (114 KB) | HTML Full-text | XML Full-text
Abstract
The spin–spin coupling constants in ethane, methylamine, and methanol have been calculated using density-functional theory (DFT), coupled-cluster singlesand-doubles (CCSD) theory, and multiconfigurational self-consistent field (MCSCF) theory so as to benchmark the performance of DFT against high-level ab initio methods and experimental data. For
[...] Read more.
The spin–spin coupling constants in ethane, methylamine, and methanol have been calculated using density-functional theory (DFT), coupled-cluster singlesand-doubles (CCSD) theory, and multiconfigurational self-consistent field (MCSCF) theory so as to benchmark the performance of DFT against high-level ab initio methods and experimental data. For each molecule, the Karplus curve has been evaluated at the three computational levels. The comparisons with ab initio methods indicate that DFT reproduces the 1J(CH), 1J(CC), and 1J(NH) one-bond couplings well but is less accurate for 1J(CN), 1J(OH), and 1J(CO). While DFT performs well for the geminal couplings 2J(HH) and 2J(CH), it tends to overestimate the vicinal 3J(HH) couplings slightly although it is sufficiently accurate for most purposes. Full article

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