The 13C Chemical Shift Tensor Principal Values and Orientations in Dialkyl Carbonates and Trithiocarbonates

Stueber, Dirk; Grant, David M.

doi:10.1006/snmr.2002.0072

Cited by 17 publications

(11 citation statements)

References 34 publications

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“…Ewald calculations performed with the modified EWALD program produced the same dependency for the rms error originally observed by KDW, i.e., that the accuracy with which V Mad is simulated increases with increasing N C and N (N T ) (51,(53)(54)(55). Furthermore, for every system under investigation, there exist minimum sizes for zones 2 and 3 that are required for a successful Ewald simulation.…”

Section: Ewald Lattice Sums and The Ewald Programsupporting

confidence: 63%

“…Generally, the largest changes in the atomic charges are observed in the first iteration step, in which the charges for the ion or molecule of interest are calculated inside the point charge array for the first time. In subsequent steps, the charge values approach self-consistency in damped oscillations within three to four iterations (53)(54)(55). This general trend is exemplified in Fig.…”

Section: Embedded Ion Methodsmentioning

confidence: 65%

“…4 using the EIM iteration data for the molecular S 2 CSCH 3 anion (47 ). Correlations between the neutral or ionic character of the system under investigation, or certain atom types, and the observed changes in the charge values have not been observed (53)(54)(55). Furthermore, it was found that a large change in partial charge that a given atom accumulates over the iteration procedure is not necessarily associated with a large change in the corresponding EIM calculated nuclear magnetic shielding tensors, or vice versa (53)(54)(55).…”

Section: Embedded Ion Methodsmentioning

confidence: 97%

“…Until now, the EIM has been applied with considerable success in the calculation of 13 C and/or 15 N nuclear magnetic shielding tensors in a wide variety of materials. Investigated were ionic compounds, as well as molecular systems involving relatively weak and strong intermolecular interactions (24,(53)(54)(55)(56)(57). This work discusses the accuracy with which the EIM reproduces the experimental chemical shift tensor principal values.…”

Section: Introductionmentioning

confidence: 99%

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The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations

Stueber

2006

Concepts Magnetic Resonance

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ABSTRACT:The nuclear magnetic shielding anisotropy of NMR active nuclei is highly sensitive to the nuclear electronic environment. Hence, measurements of the nuclear magnetic shielding anisotropy represent a powerful tool in the elucidation of molecular structure for a wide variety of materials. Quantum mechanical ab initio nuclear magnetic shielding calculations effectively complement the experimental NMR data by revealing additional structural information. The accuracy and capacity of these calculations has been improved considerably in recent years. However, the inherent problem of the limitation in the size of the systems that may be studied due to the relatively demanding computational requirements largely remains. Accordingly, ab initio shielding calculations have been performed predominantly on isolated molecules, neglecting the molecular environment. This approach is sufficient for neutral nonpolar systems, but leads to serious errors in the shielding calculations on polar and ionic systems. Conducting ab initio shielding calculations on clusters of molecules (i.e., including the nearest neighbor interactions) has improved the accuracy of the calculations in many cases. Other methods of simulating crystal lattice effects in shielding calculations that have been developed include the electrostatic representation of the crystal lattice using point charge arrays, full ab initio methods, ab initio methods under periodic boundary conditions, and hybrid ab initio/molecular dynamics methods. The embedded ion method (EIM) discussed here follows the electrostatic approach. The method mimics the intermolecular and interionic interactions experienced 347by a subject molecule or cluster in a given crystal in quantum mechanical shielding calculations with a large finite, periodic, and self-consistent array of point charges. The point charge arrays in the EIM are generated using the Ewald summation method and embed the molecule or ion of interest for which the ab initio shielding calculations are performed. The accuracy with which the EIM reproduces experimental nuclear magnetic shift tensor principal values, the sensitivity of the EIM to the parameters defining the point charge arrays, as well as the strengths and limitations of the EIM in comparison with other methods that include crystal lattice effects in chemical shielding calculations, are presented.

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Section: Ewald Lattice Sums and The Ewald Programsupporting

confidence: 63%

Section: Embedded Ion Methodsmentioning

confidence: 65%

Section: Embedded Ion Methodsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations

Stueber

2006

Concepts Magnetic Resonance

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“…Among the different point charge methods described in the literature, in this paper we consider the embedded ion method (EIM) 11 and the surface charge representation of the electrostatic embedding potential (SCREEP) 10 methods that have been developed independently in our laboratories. The EIM has been shown to improve the agreement between experimental and calculated chemical shifts in a wide variety of systems, ranging from ionic systems such as potassium carbonate and thiocarbonate 20 to systems with hydrogen bonding 12,21,22 and neutral systems with intermolecular Coulombic interactions such asˇ-HMX. 23 The SCREEP method, introduced originally by Stefanovich and Truong 24 to study catalysis, has more recently been applied to the calculation of chemical shielding by Solis et al 10 This method also shows improvements in agreement with experimental shifts comparable to those observed by the EIM method.…”

Section: Introductionmentioning

confidence: 98%

Modeling solid-state effects on NMR chemical shifts using electrostatic models

et al. 2004

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This paper presents a comparison of the embedded ion method (EIM) and the surface charge representation of the electrostatic embedding potential (SCREEP) method, two methods which can be used to calculate solid-state effects on NMR chemical shifts. The results in a selected group of compounds with known single-crystal solid-state NMR data and neutron diffraction structures, confirm that these effects are important in both (13)C and (15)N chemical shifts. The solid-state effects calculated by both methods are similar and of equal statistical quality when compared with the experimental data.

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C‐13 Chemical‐Shift Tensors in Organic Materials

Harper

Iuliucci

2014

Encyclopedia of Analytical Chemistry

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The chemical‐shift tensor provides an exquisitely sensitive measure of the electronic environment around a nucleus. The tensor is defined by a real symmetric 3 × 3 matrix with six measurable components. Single crystals are usually required to measure all six components whereas three shifts per nucleus are measurable in powders. These powder data, known as principal values , are defined as δ 11 ≥ δ 22 ≥ δ 33 . Presently, most 2D experiments measuring tensor data display the 1D isotropic spectrum along one axis and the tensor patterns for each resonance along the second dimension. Experiments most frequently used are two‐dimensional phase‐adjusted spinning sideband (2D PASS), phase corrected magic angle turning (PHORMAT), FIREMAT (five π replicated magic angle turning), RAI (recoupling of anistropic information), SUPER (separation of undistorted powder patterns by effortless recoupling), and CSA (chemical shift anisotropy) amplification. Very few simple relationships exist between principal values and structure, thus comparison with model structures from computational methods has become important. Recently, these computational methods have been used to predict structure in solids that are intractable to traditional methods. Tensor data have also been found to be extremely sensitive to crystal structure and can therefore be used to further refine some structures, including single crystal structures. The prospect of predicting entire crystal structures from 13 C tensor data and computational methods is now realistic, and a few structures have recently been determined without diffraction data.

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The 13C Chemical Shift Tensor Principal Values and Orientations in Dialkyl Carbonates and Trithiocarbonates

Cited by 17 publications

References 34 publications

The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations

The embedded ion method: A new approach to the electrostatic description of crystal lattice effects in chemical shielding calculations

Modeling solid-state effects on NMR chemical shifts using electrostatic models

C‐13 Chemical‐Shift Tensors in Organic Materials

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