Identifying Stereoisomers by ab-initio Calculation of Secondary Isotope Shifts on NMR Chemical Shieldings

Bohm, Karl‐Heinz; Banert, Klaus; Auer, Alexander A.

doi:10.3390/molecules19045301

Cited by 4 publications

(2 citation statements)

References 28 publications

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“…These numbers are obtained with CCSD(T)/qz2p calculations, but the results from a lower level of theory, HF/tz2p, are not significantly different. Similar calculations performed on endo-2fluoronorbornanes suggest that the experimental assignments of conformers made previously are mistaken (Böhm et al, 2014). For the study of the tautomeric equilibria of pyridoyl benzoyl b-diketones, deuteriuminduced isotope effects on 13 C chemical shifts are found to corroborate conclusions derived from coupling constants regarding the equilibrium positions in these asymmetric diketones (Hansen et al, 2015).…”

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confidence: 64%

Recent Advances in Theoretical and Physical Aspects of NMR Chemical Shifts

Dios

Jameson

2015

KIMIKA

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In the first part of this review, theoretical aspects of nuclear magnetic shielding include (a) general theory, for example, newly developed approaches in relativistic theory of nuclear shielding, the relation between the spin-rotation tensor and shielding in relativistic theory, ab initio methods for treating open shell systems and a complete theory of chemical shifts in paramagnetic systems, the link between the definitions of the elusive concepts aromaticity and anti-aromaticity and the magnetic properties: the magnetizability tensor and the nuclear magnetic shielding tensor via delocalized electron currents and electron current maps, (b) ab initio and DFT calculations, both relativistic and non-relativistic, for various nuclei in various molecular systems using various levels of theoretical treatment. Physical aspects include (a) anisotropy of the shielding tensor, usually from solid state measurements, and calculations to support these, (b) shielding surfaces and rovibrational averaging, paying special attention to the sensitive relationship between shielding and bond angles or torsion angles that makes shielding such a powerful tool for structural/conformational determination in macromolecules, (c) chemical shifts that arise from isotopic substitution of NMR nucleus or neighboring nuclei, (d) intermolecular effects on nuclear shielding, and (e) absolute shielding scales.

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confidence: 64%

Recent Advances in Theoretical and Physical Aspects of NMR Chemical Shifts

Dios

Jameson

2015

KIMIKA

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“…Such isotope effects have been observed and investigated for global properties such as dipole moments [ 2 , 3 ] and polarizabilities [ 4 , 5 ] but are most interesting for atom-specific spectroscopic properties such as electron spin resonance (ESR) [ 6 , 7 ], spin rotation constants [ 8 , 9 ] and above all nuclear magnetic resonance (NMR) isotopic shifts, in particular on chemical shielding constants [ 10 , 11 , 12 , 13 , 14 , 15 ]. NMR isotopic shifts have been used to investigate inter- and intramolecular hydrogen bonds [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ] and salt bridges [ 21 , 22 ] as well as the backbone conformation in proteins [ 23 , 24 , 25 ] and local stereochemistry [ 26 , 27 , 28 , 29 ].…”

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confidence: 99%

The Structure of the “Vibration Hole” around an Isotopic Substitution—Implications for the Calculation of Nuclear Magnetic Resonance (NMR) Isotopic Shifts

Gräfenstein¹

2020

Molecules

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Calculations of nuclear magnetic resonance (NMR) isotopic shifts often rest on the unverified assumption that the “vibration hole”, that is, the change of the vibration motif upon an isotopic substitution, is strongly localized around the substitution site. Using our recently developed difference-dedicated (DD) second-order vibrational perturbation theory (VPT2) method, we test this assumption for a variety of molecules. The vibration hole turns out to be well localized in many cases but not in the interesting case where the H/D substitution site is involved in an intra-molecular hydrogen bond. For a series of salicylaldehyde derivatives recently studied by Hansen and co-workers (Molecules 2019, 24, 4533), the vibrational hole was found to stretch over the whole hydrogen-bond moiety, including the bonds to the neighbouring C atoms, and to be sensitive to substituent effects. We discuss consequences of this finding for the accurate calculation of NMR isotopic shifts and point out directions for the further improvement of our DD-VPT2 method.

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Efficient calculation of NMR isotopic shifts: Difference-dedicated vibrational perturbation theory

Gräfenstein

2019

The Journal of Chemical Physics

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We present difference-dedicated second-order vibrational perturbation theory (VPT2) as an efficient method for the computation of nuclear magnetic resonance (NMR) isotopic shifts, which reflect the geometry dependence of the NMR property in combination with different vibration patterns of two isotopologues. Conventional calculations of isotopic shifts, e.g., by standard VPT2, require scanning the geometry dependence over the whole molecule, which becomes expensive rapidly as the molecule size increases. In DD-VPT2, this scan can be restricted to a small region around the substitution site. At the heart of DD-VPT2 is a set of localized vibration modes common to the two isotopologues and designed such that the difference between the vibration patterns is caught by a small subset of them (usually fewer than 10). We tested the DD-VPT2 method for a series of molecules with increasing size and found that this method provides results with the same quality as VPT2 and in good agreement with the experiment, with computational savings up to 95% and less numerical instabilities. The method is easy to automatize and straightforward to generalize to other molecular properties.

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Identifying Stereoisomers by ab-initio Calculation of Secondary Isotope Shifts on NMR Chemical Shieldings

Cited by 4 publications

References 28 publications

Recent Advances in Theoretical and Physical Aspects of NMR Chemical Shifts

Recent Advances in Theoretical and Physical Aspects of NMR Chemical Shifts

The Structure of the “Vibration Hole” around an Isotopic Substitution—Implications for the Calculation of Nuclear Magnetic Resonance (NMR) Isotopic Shifts

Efficient calculation of NMR isotopic shifts: Difference-dedicated vibrational perturbation theory

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