<i>Ab initio</i> calculations of NMR chemical shifts

Casabianca, Leah B.; Dios, Angel C. de

doi:10.1063/1.2816784

Cited by 107 publications

(73 citation statements)

References 219 publications

(152 reference statements)

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“…[12] Nevertheless, they also show that the accurate calculation of the chemical shifts is not straight forward and that probably higher levels of theory combined with larger basis sets and inclusion of solvent effects (and relativistic effects) are needed to get an accuracy of less than 5 ppm for all carbons. [38][39][40][41][42][43][44] But even the qualitative description is very helpful to understand the electronic effects resulting from structural variations. Two such effects were analyzed in detail:…”

Section: Discussionmentioning

confidence: 99%

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Small changes—Huge influences: NMR chemical shifts of Ni(II) complexes with polar substrates

Frank

Berkefeld

Drexler

et al. 2013

Int J of Quantum Chemistry

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Neutral Ni(II) complexes have been shown to be highly valuable as robust and versatile catalysts in olefin polymerization. But they show reduced reactivity when the polar monomers methyl acrylate and vinyl acetate are incorporated. To get further insight into this behavior, NMR chemical shift calculations were performed on the system [(N,O) Ni (H) (PMe3)] 1 (N,O = $\kappa ^2$‐N,O‐{2,6‐(3,5‐(F3C)2C6H3)2C6H3)NC(H)‐3,5‐I2‐2‐O‐C6H2}). The chemical shifts show reasonable agreement with experiment but are also extremely influenced by geometrical features of the complex as well as the inserted substrate. The first prominent feature, the low‐field shift of the Ccarbonyl in the incorporated monomer, can only be reproduced when it is in close proximity to the Ni and in this way hinders the attack of a new monomer. Second, the almost 100 ppm difference in the chemical shift of the carbon of the two substrates directly bound to Ni can be reasoned by the different directionality of polarization as disclosed by natural bond orbital (NBO) analysis. © 2013 Wiley Periodicals, Inc.

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Section: Discussionmentioning

confidence: 99%

“…It is known from the literature that the influence of heavy elements on the chemical shift is difficult to predict. [38,39] For such a heavy nucleus relativistic effects already play a nonnegligible role. The use of effectivecore potentials did not lead to an improvement (data not shown).…”

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confidence: 99%

Small changes—Huge influences: NMR chemical shifts of Ni(II) complexes with polar substrates

Frank

Berkefeld

Drexler

et al. 2013

Int J of Quantum Chemistry

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“…In the course of that work we showed, among other things, the relative merits of using various functionals, including the hybrid variants WP04 and WC04, which (1) (1) we had previously developed specifically for computing proton and carbon chemical shifts 11 , to provide computed data that best distinguish the members of this family of albeit only modestly complex structures. We have chosen to present the details of this protocol in the context of the analysis of 1-cis versus 1-trans.…”

Section: Box 1 | Two Case Studies: Hexacyclinol (Constitution) and Vamentioning

confidence: 99%

“…Of the three important classes of primary NMR data-chemical shifts, coupling constants and relative integrated signal intensity-the first is the most diagnostic of the local chemical and magnetic environment (i.e., the nuclei's structural surroundings) and, arguably, the most reliably addressable by computational methods 1,2 . Accordingly, this protocol deals only with computational aspects of chemical shifts, and only proton and carbon nuclei are considered.…”

Section: Introductionmentioning

confidence: 99%

A guide to small-molecule structure assignment through computation of (1H and 13C) NMR chemical shifts

2014

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this protocol is intended to provide chemists who discover or make new organic compounds with a valuable tool for validating the structural assignments of those new chemical entities. experimental 1 H and/or 13 c nMr spectral data and its proper interpretation for the compound of interest is required as a starting point. the approach involves the following steps: (i) using molecular mechanics calculations (with, e.g., MacroModel) to generate a library of conformers; (ii) using density functional theory (DFt) calculations (with, e.g., Gaussian 09) to determine optimal geometry, free energies and chemical shifts for each conformer; (iii) determining Boltzmann-weighted proton and carbon chemical shifts; and (iv) comparing the computed chemical shifts for two or more candidate structures with experimental data to determine the best fit. For a typical structure assignment of a small organic molecule (e.g., fewer than ~10 non-H atoms or up to ~180 a.m.u. and ~20 conformers), this protocol can be completed in ~2 h of active effort over a 2-d period; for more complex molecules (e.g., fewer than ~30 non-H atoms or up to ~500 a.m.u. and ~50 conformers), the protocol requires ~3-6 h of active effort over a 2-week period. to demonstrate the method, we have chosen the analysis of the cis-versus the trans-diastereoisomers of 3-methylcyclohexanol (1-cis versus 1-trans). the protocol is written in a manner that makes the computation of chemical shifts tractable for chemists who may otherwise have only rudimentary computational experience. this method certainly has value, the example described next shows that when one moves to the consideration of molecules bearing more than one stereocenter, this approach is no longer adequate.Consider the case of the trans-versus the cis-diastereomers of 3-methylcyclohexanol (1-trans and 1-cis, respectively). The experimental 1 H NMR spectra for 1-trans and 1-cis are shown in Figure 1a,b (see Supplementary Data 1 for a full listing of actual chemical shift values). There are substantial differences in these two spectra, especially within the upfield 0.7-2.1 p.p.m. range. Clearly, it would be valuable if computational approaches could reproduce these sorts of differences sufficiently well to allow confident assignment of structure.Common software packages that use empirical (often increment-based) compilations of chemical shift information (e.g., tabulated shift increments or databases of known spectral data) allow users to predict the chemical shifts of a given input structure. These include 'ChemNMR' within ChemBioDraw (also known as ChemDraw) and 'C+H NMR Predictor and DB' within the ACD/Labs software suite. These methods sometimes can be sufficient for the task of resolving constitutional structural assignments. However, when issues associated with relative configuration are considered, increment-based methods are decidedly ill-equipped. Analysis of structures 1-trans and 1-cis by each of these programs quickly reveals these limitations, even for these simple structures. Namely, because Che...

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“…NMR chemical shielding was calculated using the gauge-invariant atomic orbital (GIAO) method [25][26][27][28]. Atomic coordinates for a single molecule were extracted from the crystal structure and a full optimization was done under the level of B3LYP/6-311++g(d,p).…”

Section: Nmr Chemical Shift Calculations and Conformational Analysismentioning

confidence: 99%

Crystal packing and crystallization tendency from the melt of 2-((2-ethylphenyl)amino)nicotinic acid

Kalra

Zhang

Parkin

et al. 2017

Zeitschrift Für Kristallographie - Crystalline Materials

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2-((2-ethylphenyl)amino)nicotinic acid (2EPNA) was synthesized and its crystal structure was determined. It was observed that alkylation of the phenyl ring with ethyl group disrupts the planar conformation of the molecule by steric repulsion, resulting in formation of an acid-pyridine heterosynthon (instead of acid-acid homosynthon) in the crystal. Crystallization tendency from the melt state of the polymorph was studied by differential scanning calorimetry (DSC). It was revealed that this compound could form a very stable amorphous phase on melt quenching and not crystallize even on re-heating. The formation of acid-pyridine hydrogen bonding in the amorphous state is believed to be responsible for its good glass forming ability.

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Ab initio calculations of NMR chemical shifts

Cited by 107 publications

References 219 publications

Small changes—Huge influences: NMR chemical shifts of Ni(II) complexes with polar substrates

Small changes—Huge influences: NMR chemical shifts of Ni(II) complexes with polar substrates

A guide to small-molecule structure assignment through computation of (1H and 13C) NMR chemical shifts

Crystal packing and crystallization tendency from the melt of 2-((2-ethylphenyl)amino)nicotinic acid

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