Solvent Effects on Nitrogen Chemical Shifts

Andersson, Hanna; Carlsson, A.; Nekoueishahraki, Bijan; Brath, Ulrika; Erdélyi, Máté

doi:10.1016/bs.arnmr.2015.04.002

Cited by 19 publications

(20 citation statements)

References 211 publications

(410 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The 15 N NMR chemical shift, δ 15 N, is recognized to be a sensitive tool for the assessment of the coordinative bonds of nitrogen heterocycles. 54 , 69 It has previously been used for the characterization of halogen bonded complexes. 45 , 49 , 50 , 70 , 71 Upon formation of pyridine-based [N···I···N] + complexes, analogous to nonsubstituted 1a and 2a , ∼100 ppm 15 N chemical shift changes, δ 15 N coord , are induced.…”

Section: Resultsmentioning

confidence: 99%

Substituent Effects on the [N–I–N]⁺ Halogen Bond

et al. 2016

Self Cite

View full text Add to dashboard Cite

We have investigated the influence of electron density on the three-center [N–I–N]+ halogen bond. A series of [bis(pyridine)iodine]+ and [1,2-bis((pyridine-2-ylethynyl)benzene)iodine]+ BF4– complexes substituted with electron withdrawing and donating functionalities in the para-position of their pyridine nitrogen were synthesized and studied by spectroscopic and computational methods. The systematic change of electron density of the pyridine nitrogens upon alteration of the para-substituent (NO2, CF3, H, F, Me, OMe, NMe2) was confirmed by 15N NMR and by computation of the natural atomic population and the π electron population of the nitrogen atoms. Formation of the [N–I–N]+ halogen bond resulted in >100 ppm 15N NMR coordination shifts. Substituent effects on the 15N NMR chemical shift are governed by the π population rather than the total electron population at the nitrogens. Isotopic perturbation of equilibrium NMR studies along with computation on the DFT level indicate that all studied systems possess static, symmetric [N–I–N]+ halogen bonds, independent of their electron density. This was further confirmed by single crystal X-ray diffraction data of 4-substituted [bis(pyridine)iodine]+ complexes. An increased electron density of the halogen bond acceptor stabilizes the [N···I···N]+ bond, whereas electron deficiency reduces the stability of the complexes, as demonstrated by UV-kinetics and computation. In contrast, the N–I bond length is virtually unaffected by changes of the electron density. The understanding of electronic effects on the [N–X–N]+ halogen bond is expected to provide a useful handle for the modulation of the reactivity of [bis(pyridine)halogen]+-type synthetic reagents.

show abstract

Section: Resultsmentioning

confidence: 99%

Substituent Effects on the [N–I–N]⁺ Halogen Bond

et al. 2016

Self Cite

View full text Add to dashboard Cite

show abstract

“…The 14 N nucleus (I = 1) has a high natural abundance (99.63%), very low gyromagnetic ratio (~1.938 × 10 7 rad T −1 s −1 ) and small receptivity (~1 × 10 −3 ) with respect to that of 1 H. Furthermore, relatively large quadrupolar coupling constants and, thus, broad resonances limit applications of this isotope to nitrogen sites with spherical electronic symmetry around the nitrogen nucleus. The 15 N isotope has a spin quantum number I = 1/2, very low natural abundance of 0.37%, very low gyromagnetic ratio (−2.71 × 10 7 rad T −1 s −1 ) and extremely low receptivity (0.39 × 10 −5 ) with respect to that of 1 H and, thus, has been found very limited applications [ 53 ]. Therefore, for the purpose of the present review article only 1 H, 13 C and 31 P nuclei will be discussed.…”

Section: Nmr Structural and Analytical Parametersmentioning

confidence: 99%

High Resolution NMR Spectroscopy as a Structural and Analytical Tool for Unsaturated Lipids in Solution

et al. 2017

View full text Add to dashboard Cite

Mono- and polyunsaturated lipids are widely distributed in Nature, and are structurally and functionally a diverse class of molecules with a variety of physicochemical, biological, medicinal and nutritional properties. High resolution NMR spectroscopic techniques including 1H-, 13C- and 31P-NMR have been successfully employed as a structural and analytical tool for unsaturated lipids. The objective of this review article is to provide: (i) an overview of the critical 1H-, 13C- and 31P-NMR parameters for structural and analytical investigations; (ii) an overview of various 1D and 2D NMR techniques that have been used for resonance assignments; (iii) selected analytical and structural studies with emphasis in the identification of major and minor unsaturated fatty acids in complex lipid extracts without the need for the isolation of the individual components; (iv) selected investigations of oxidation products of lipids; (v) applications in the emerging field of lipidomics; (vi) studies of protein-lipid interactions at a molecular level; (vii) practical considerations and (viii) an overview of future developments in the field.

show abstract

“…It has been shown that the solvent may significantly alter the observed shifts. [19] One obvious question is whether there is any transferability for the fitted scaling factors between different solvents with the same level of theory for calculation. Can the fitted empirical scaling factors in one solvent apply to other solvents without re-parameterization?…”

Section: Transferability For Scaling Factors Between Chcl 3 and Dmsomentioning

confidence: 99%

Towards an Accurate Prediction of Nitrogen Chemical Shifts by Density Functional Theory and Gauge‐Including Atomic Orbital

Gao

Wang

2018

Advcd Theory and Sims

View full text Add to dashboard Cite

An efficient, yet accurate, computational protocol for predicting nitrogen nuclear magnetic resonance (NMR) chemical shifts based on density functional theory and the gauge-including atomic orbital approach is proposed. A database of small and relatively rigid compounds containing nitrogen atoms is compiled. Scaling factors for the linear correlation between experimental 15 N chemical shifts and calculated isotropic shielding constants are systematically investigated with seven different levels of theory in both chloroform and dimethyl sulfoxide, two commonly used solvents for NMR experiments. The best method yields a root-mean-square deviation of about 5.30 and 7.00 ppm in CHCl 3 and dimethyl sulfoxide (DMSO), respectively. Moreover, another set of scaling factors for -NH 2 chemical shifts is also proposed based on a separate database with three levels of theory. Furthermore, it is encouraging that a reasonable transferability for the linear correlation is found between these two solvents. This finding will enable broader applications of the developed empirical scaling factors to other commonly used solvents in NMR experiments. The consistency between theoretical predictions and experimental results for structural elucidations is illustrated for selected examples including regioisomers, tautomers, oxidation states, and protonated structures.

show abstract

Solvent Effects on Nitrogen Chemical Shifts

Cited by 19 publications

References 211 publications

Substituent Effects on the [N–I–N]⁺ Halogen Bond

Substituent Effects on the [N–I–N]⁺ Halogen Bond

High Resolution NMR Spectroscopy as a Structural and Analytical Tool for Unsaturated Lipids in Solution

Towards an Accurate Prediction of Nitrogen Chemical Shifts by Density Functional Theory and Gauge‐Including Atomic Orbital

Contact Info

Product

Resources

About

Solvent Effects on Nitrogen Chemical Shifts

Cited by 19 publications

References 211 publications

Substituent Effects on the [N–I–N]+ Halogen Bond

Substituent Effects on the [N–I–N]+ Halogen Bond

High Resolution NMR Spectroscopy as a Structural and Analytical Tool for Unsaturated Lipids in Solution

Towards an Accurate Prediction of Nitrogen Chemical Shifts by Density Functional Theory and Gauge‐Including Atomic Orbital

Contact Info

Product

Resources

About

Substituent Effects on the [N–I–N]⁺ Halogen Bond

Substituent Effects on the [N–I–N]⁺ Halogen Bond