Low-temperature carbon-13 magnetic resonance in solids. 5. Chemical shielding anisotropy of the 13CH2 group

Facelli, Julio C.; Orendt, Anita M.; Beeler, Alvin J.; Solum, Mark S.; Depke, Gisbert; Malsch, K.-D.; Downing, J. W.; Murthy, P. S.; Grant, David M.; Michl, Josef

doi:10.1021/ja00310a001

Cited by 40 publications

(25 citation statements)

References 2 publications

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“…Apparently this is the case when the bond angles on the carbon are smaller than 90°. This corresponds with the results of Facelli et al who reported the angular dependence of the CC bond component of the chemical shift tensor based on IGLO calculations (13).…”

Section: Calculationssupporting

confidence: 92%

Extremely Fast Calculation of ¹³C Chemical Shift Tensors Using the Bond Polarization Theory

Sternberg

Prieß

1999

Modeling NMR Chemical Shifts

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The semi-empirical bond polarization theory provides a fast method for the calculation of 13 C chemical shift tensors with an accuracy level comparable to ab initio methods for most molecules. There are no restrictions in the size of the molecular system, so that the method can be applied to large molecules or crystal lattices. Chemical shift calculations were carried out for several small molecules and compared to ab initio results. Additionally the calculated chemical shift tensor for the fullerence C 60 is presented.The calculation of magnetic shielding parameters are of great importance for the interpretation of the chemical shift in NMR spectra. However, the calculation of chemical shift tensors is still an adventurous task. Currently isotropic chemical shifts can be estimated from empirical increments and correlations and these estimates are in most cases precise enough to reveal the topology or constitution of a molecule. However, if tensorial chemical shifts should be estimated from the structure of a molecule, in most cases ab initio quantum chemical calculations on the IGLO (1), LORG (2) or GIAO (3) level must be carried out. In general this approach is limited to medium size molecules and strictly speaking it reflects the situation of an isolated molecule in the gas phase. De Dios et al proposed a simulation scheme for the calculation of magnetic shielding parameters in amino acids and peptides which includes the polarizing effects of surrounding molecules (4).The authors of this work proposed a semi-empirical scheme for the calculation of l3 C chemical shift tensors based on the bond polarization theory (5). This method can reproduce 13 C chemical shift tensors with deviations from experiment comparable to the errors of the ab initio methods. One major advantage is that the calculations can be performed for large molecular systems with hundreds of atoms even on a PC computer. In contrast to the ab initio method a set of empirical parameters is needed for the calculations. In the case of the bond polarization theory these parameters can be estimated directly from experimental chemical shifts solving a set of linear equations.Once the semi-empirical parameters are determined, the bond polarization method can calculate the chemical shift values very quickly. In this work we compare

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Section: Calculationssupporting

confidence: 92%

Extremely Fast Calculation of ¹³C Chemical Shift Tensors Using the Bond Polarization Theory

Sternberg

Prieß

1999

Modeling NMR Chemical Shifts

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“…There are numerous examples of this in the literature, but perhaps one of the most striking one is the angular dependence of the principal components of the 13 C chemical shielding tensors in cyclopropane, cyclobutane, and cyclopentane (66). This dramatic effect is depicted in Fig.…”

Section: Chemical Shielding Dependence On Molecular Structurementioning

confidence: 93%

“…CC is approximately perpendicular to the ring plane, AA is in the plane along the direction bisecting the HCH angle, and BB is also in the plane perpendicular to AA . From Facelli et al (66 ).…”

Section: Hybridization Effects On Chemical Shieldingsmentioning

confidence: 99%

Calculations of chemical shieldings: Theory and applications

Facelli

2004

Concepts Magnetic Resonance

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105

127

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ABSTRACT:This article presents a discussion of the origin of the chemical shieldings, which is followed by a rigorous derivation of quantum mechanical formula for their exact calculation and a discussion of the necessary approximations that make these calculations feasible. Comprehensive information on the resources, software and hardware needed for the calculations is given followed by several examples of actual quantum chemical calculations of chemical shieldings. These examples are used to demonstrate how accurate shielding calculations can be used to help the NMR practitioner to solve practical chemical and structural problems.

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“…It seems, however, that the methylene C-1 0 is rather rigid, since its measured CST is comparable to similar compounds. 34,35 The highest CSA was found for C-4 in both the conformers. The shift tensors of both C-1 nuclei in cone are very similar to the corresponding data in 1,3-alt.…”

Section: Liquid-and Solid-state Spectra Chemical Shift Tensormentioning

confidence: 95%

Reorientational dynamics of two isomers of thiacalix[4]arene

Lang

Tošner

Lhoták

et al. 2003

Magnetic Reson in Chemistry

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Molecular reorientation and local mobility of two isomers of 25,26,27,28-tetrapropoxy-2,8,14,20-tetrathiacalix[4]arene, cone and 1,3-alternate, were studied by means of NMR relaxation. The chemical shift anisotropy of 13 C nuclei was determined in the solid state. Nuclear relaxation due to dipole-dipole interaction and chemical shift anisotropy was analysed in the framework of the Lipari-Szabo approach. The aromatic core of both isomers was found rigid on the subnanosecond time scale. The amplitude of the local motion of the lower rim propoxy substituents increases towards the methyl ends. The methylene groups of the propoxy residues of the cone isomer possess more motional freedom than in the 1,3-alternate, where they are sterically hindered by the adjacent aromatic rings. Global reorientation of the cone is slower than the motion of the 1,3-alternate, which rotates partly anisotropically.

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Low-temperature carbon-13 magnetic resonance in solids. 5. Chemical shielding anisotropy of the 13CH2 group

Cited by 40 publications

References 2 publications

Extremely Fast Calculation of ¹³C Chemical Shift Tensors Using the Bond Polarization Theory

Extremely Fast Calculation of ¹³C Chemical Shift Tensors Using the Bond Polarization Theory

Calculations of chemical shieldings: Theory and applications

Reorientational dynamics of two isomers of thiacalix[4]arene

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Low-temperature carbon-13 magnetic resonance in solids. 5. Chemical shielding anisotropy of the 13CH2 group

Cited by 40 publications

References 2 publications

Extremely Fast Calculation of 13C Chemical Shift Tensors Using the Bond Polarization Theory

Extremely Fast Calculation of 13C Chemical Shift Tensors Using the Bond Polarization Theory

Calculations of chemical shieldings: Theory and applications

Reorientational dynamics of two isomers of thiacalix[4]arene

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Extremely Fast Calculation of ¹³C Chemical Shift Tensors Using the Bond Polarization Theory

Extremely Fast Calculation of ¹³C Chemical Shift Tensors Using the Bond Polarization Theory