Quantum-chemical calculations of NMR chemical shifts of organic molecules: I. Phosphines, phosphine oxides, and phosphine sulfides

Abstract

The accuracy in the calculation of 31 P NMR chemical shifts in the series of the simplest phosphines, phosphine oxides, and phosphine sulfides was estimated in terms of the Hartree-Fock self-consistent final perturbation theory and density functional theory with different basis sets. The best agreement between the calculated and experimental data was achieved at the DFT/B3LYP/IGLO-III level of theory.NMR spectroscopy is one of the most important experimental tools for studying steric and electronic structures of molecules. In this connection, development of theoretical methods for the calculation of NMR parameters, in particular chemical shifts, becomes significant. Such methods could provide invaluable help both in assignment of signals in the spectra of complex organic molecules and determination of their structure and in conformational analysis, configurational assignment, studying intra-and intermolecular interactions, and prediction of the reactivity of organic compounds [1,2]. The present communication opens a new series of our theoretical works on the calculation of NMR shielding constants (chemical shifts) of nuclei in organic molecules at a high level of modern quantum chemistry.At present, most studies concerned with calculations of magnetic shielding constants make use of approaches based on the density functional theory (DFT) which ensures fairly good results for 1 H, 13 C, and 15 N chemical shifts of natural compounds [3, 4] and organometallic complexes [5,6]. These results are very useful for studying tautomeric equilibria and proving formation of intramolecular hydrogen bonds [7,8]. On the other hand, calculations on shielding constants of nuclei belonging to the third and higher Periods of the Periodic Table, e.g., 31 P, were reported in a few publications. Nevertheless, the available data attract considerable interest, taking into account exceptionally broad range of variation of phosphorus chemical shifts (up to 500 ppm) and important structural information that could be obtained therefrom. Analysis of various factors affecting the accuracy of calculation of δ P values for organophosphorus compounds was performed only in some recent studies [9][10][11]; in particular, comparison of different electron density functionals, basis sets, and methods for consideration of gauge invariance.In the present work we estimated the accuracy in the calculation of 31 P shielding constants (chemical shifts), depending on the calculation method (level of theory) and basis set (primarily its size and flexibility) for effective and appropriate use of these parameters in stereochemical studies on organophosphorus compounds. As subjects for study we selected nine simplest organophosphorus compounds of different natures: phosphines R 3 P (I-III), phosphine oxides R 3 P=O (IV-VI), and phosphine sulfides R 3 P=S (VII-IX) containing methyl, ethyl, and methoxy groups on the phosphorus (I, IV, VII, R = Me; II, V, VIII, R = Et; III, VI, IX, R = MeO).All calculations of 31 P chemical shifts were performed for the most favora...

Quantum-chemical calculations of chemical shifts in NMR spectra of organic molecules: V. Stereochemical structure of unsaturated phosphonic acids dichlorides from 31P NMR spectral data

“…In the table the theoretical values of 31 Р NMR chemical shifts δ calc (ppm) are presented referred to external 85% aqueous H 3 PO 4 recalculated by the equation taken from [13] that we have successfully used in our previous publications [1,2,12,14]:…”

Applications of nuclear shielding

“…The accuracy in the calculation of 31 P NMR chemical shifts in the series of the simplest phosphines, phosphine oxides and phosphine sulfides was estimated in terms of the Hartree-Fock self-consistent final perturbation theory and DFT with different basis sets. 380 The synthesis of new phthalocyanine iron(ii) (FePc) based coordination complexes 2-7, their structural characterisation by multinuclear NMR ( 1 H, 13 C, 15 N, 31 P, 57 Fe), and their use as improved sensitive and cheap optical NO 2 sensors is described. 381 The effect of cholesterol (5-40 mol%) on the magnetic induced orientation of sphingomyelin/cholesterol multilamellar vesicles (MLVs) is examined using static solid state 31 P NMR spectroscopy.…”

Quantum-chemical calculation of NMR chemical shifts of organic molecules: III. Intramolecular coordination effects on the 31P NMR chemical shifts of phosphorylated N-vinylazoles

“…Purely nonrelativistic calculations of 31 P NMR shielding constants (Gaussian 03 [13]) were also performed for general comparison and estimation of contribution of relativistic effects. Triple-split Kutzelnigg IGLO-III basis set [14] was used in nonrelativistic calculations, for it ensured the best results in the calculations of δ P for phosphines and phosphine oxides [5]. Calculations with account taken of spin-orbital interactions were performed using Slater-type double-split DZP basis set [15,16].…”

“…The present communication continues the series of studies involving ab initio calculations on shielding constants [1,5]; in this work we examined effects of intramolecular coordination of the phosphorus atom in trichloro[2-(1H-pyrazol-1-yl)ethenyl]phosphonium hexachlorophosphate(V) (I) and 1,1,1,1-tetrachloro-1H-1λ 6 -pyrazolo[1,2-a][1,2,3]diazaphosphol-8-ium-1-ide (II). Phosphorylation of 1-vinyl-1H-pyrazole with PCl 5 gave Z isomer of salt I, which was stable at room temperature; it underwent Z-E isomerization at elevated temperature (Scheme 2).…”