Density-functional computation of 93Nb NMR chemical shifts

Abstract

The (15)N and (13)C chemical shifts of 6-(fluoro, chloro, bromo, and iodo)purine 2'-deoxynucleoside derivatives in deuterated chloroform were measured. The (15)N chemical shifts were determined by the (1)H-(15)N HMBC method, and complete (15)N chemical-shift assignments were made with the aid of density functional theory (DFT) calculations. Inclusion of solvation effects significantly improved the precision of the calculations of (15)N chemical shifts. Halogen-substitution effects on the (15)N and (13)C chemical shifts of purine rings are discussed in the context of DFT results. The experimental coupling constants for (19)F interacting with (15)N and (13)C of the 6-fluoropurine 2-deoxynuleoside are compared with those from DFT calculations.

Fluorinated Weakly Coordinating Anions [M(hfip)6]– (M = Nb, Ta): Syntheses, Structural Characterizations and ­Computations

“…This is at the highfield border of the chemical shift range defined by Lapina et al by MAS‐NMR for NbO 6 polyhedra in solid materials 32. In former investigations for niobium in high oxidation states,33,34 a better shielding was found with increasing electronegativity of the substituents, which is in accordance with this observation. The shift difference of about 80 ppm between the 93 Nb signals of the two salts is not only due to the different solvents.…”

Aggregation and Solvation of Chiral N,P‐Amide Ligands in Coordinating Solvents: A Computational and NMR Spectroscopic Study

“…Theoretical calculations make it feasible to assign but also confirm the NMR spectra and have been used extensively for various organometallic compounds. [41,[43][44][45][46][47][48][49][50][51] In theoretical calculations, the NMR spectroscopic chemical shifts (and shieldings) are very sensitive to the basis sets and in general the highest level method and basis set should be used. [52][53][54][55] Juxtaposition of quantum-chemical-calculated NMR spectroscopic shifts together with the experimental data and various two-dimensional NMR spectroscopic approaches such as HMBC, HSQC and COSY are other ways of facilitating the assignment of the NMR spectra.…”