Density functional calculations of NMR chemical shifts and ESR g-tensors

An overview is given on recent advances of density functional theory (DFT) as applied to the calculation of nuclear magnetic resonance (NMR) chemical shifts and electron spin resonance (ESR) g-tensors. This is a new research area that has seen tremendous progress and success recently; we try to present some of these developments. DFT accounts for correlation effects efficiently. Therefore, it is the only first-principle method that can handle NMR calculations on large systems like transition-metal complexes. Relativistic effects become important for heavier element compounds; here we show how they can be accounted for. The ESR g-tensor is related conceptually to the NMR shielding, and results of g-tensor calculations are presented. DFT has been very successful in its application to magnetic properties, for metal complexes in particular. However, there are still certain shortcomings and limitations, e.g., in the exchange-correlation functional, that are discussed as well. Received: 24 October 1997 / Accepted: 19 December 1997     

Structure-NMR chemical shift relationships for novel functionalized derivatives of quinoxalines

(1)H, (13)C and (15)N NMR chemical shifts for a variety of novel quinoxalines were determined by different 2D methods and were calculated using the GIAO DFT approach. Comparison with experimental data shows good correlations in the case of (1)H, (13)C and (15)N chemical shifts. Different combinations of basis sets were tested. In non-polar solvents quinoxalines exist as dimers owing to strong hydrogen bonding. Calculations for dimers improve the correlation between experiment and theory. Additive empirical methods for estimating chemical shifts have drawbacks and have to be used with a great care for this type of compound.     

Ring currents as probes of the aromaticity of inorganic monocycles : P5-, As5-, S2N2, S3N3-, S4N3+, S4N42+, S5N5+, S42+ and Se42+

Current-density maps were calculated by the ipsocentric CTOCD-DZ/6-311G** (CTOCD-DZ=continuous transformation of origin of current density-diamagnetic zero) approach for three sets of inorganic monocycles: S(4) (2+), Se(4) (2+), S(2)N(2), P(5) (-) and As(5) (-) with 6 pi electrons; S(3)N(3) (-), S(4)N(3) (+) and S(4)N(4) (2+) with 10 pi electrons; and S(5)N(5) (+) with 14 pi electrons. Ipsocentric orbital analysis was used to partition the currents into contributions from small groups of active electrons and to interpret the contributions in terms of symmetry- and energy-based selection rules. All nine systems were found to support diatropic pi currents, reinforced by sigma circulations in P(5) (-), As(5) (-), S(3)N(3) (-), S(4)N(3) (+), S(4)N(4) (2+) and S(5)N(5) (+), but opposed by them in S(4) (2+), Se(4) (2+) and S(2)N(2). The opposition of pi and sigma effects in the four-membered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).     

Applicability of the H NMR chemical shifts computed by the ab initio/GIAO-HF methodology to the study of geometrical features of Zn-porphyrin dimers

Several porphyrin dimers have been newly designed and synthesized to construct assemblies with 1,4-diazabicyclo[2.2.2]octane (DABCO) as a bidentate binding ligand. Semi empirical (AM1) and ab initio calculations have been used to study the assemblies generated by the organization of dimers and DABCO, including the computation of ¹H NMR complexation-induced chemical shifts using the ab initio/GIAO methodology. The diagnostic capacity of the theoretical method has been applied to explain experimental results and geometrical features of the complexes.     

The effect of the solvents on the specific intramolecular C-H...N interactions studied by1H NMR spectroscopy

The analysis of the effect of the solvents on the proton chemical shifts in¹H NMR spectra of 2-vinyloxypyridine indicates that the C—H...N interaction of weak intramolecular hydrogen bond type hinders the formation of intermolecular hydrogen C—H...X and C-H... bonds. The protonating solvents reduce the intramolecular C—H...N interaction due to association with the N atom of the pyridine cycle.Translated fromIzvestiya Akademii Nauk. Seriya Khimieheskaya, No. S, pp. 1202–1204, May, 1996.     

H, C, N NMR, ESI mass spectral and single crystal X-ray structural characterization of three spiro[pyrrolidine-2,3′-oxindoles]

Three spiro[pyrrolidine-2,3′-oxindoles], 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-phenyl-spiro[3H-indole-3,3′-[3H]-pyrrolizine]-2′-carboxylic acid methyl ester (1), 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-phenyl-spiro[3H-indole-3, 3′-[3H]-pyrrolizine] (2) and 1,1′,2,2′,5′,6′,7′,7′a-octahydro-2-oxo-1′-nitro-2′-(4″-chlorophenyl)-spiro[3H-indole-3,3′-[3H]-pyrrolizine] (3) have been synthesized and their ¹H, ¹³C and ¹⁵N spectra assigned. The chemical shift assignments are based on Pulsed Field Gradient (PFG) Double Quantum Filter (DQF) ¹H, ¹H correlation spectroscopy (COSY), PFG ¹H, ¹³C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG ¹H,X (X = ¹³C and ¹⁵N) Heteronuclear Multiple Bond Correlation (HMBC) experiments. The single crystal X-ray structures of 1–3 have been determined. Compounds 1 and 2 crystallized in monoclinic space group C2/c and compound 3 in monoclinic space group P2₁/c, respectively. Also the ESI-TOF MS data of 1–3 are given.     

A Quantitative Determination of the Interaction of Pentamethylenetetrazole with the Sodium Ion by Sodium-23 NMR

The importance of the sodium ion transport in biological systems is well known. Numerous studies have dealt with compounds which affect ion transport across membrane systems. However, the mechanism of ion transport across the membrane is still not clear. Hence it is of interest to investigate the interaction of the sodium ion with biologically active compounds in a system where the complex membrane is absent. Such a method of investigation must be able to detect very weak interactions. Sodium-23 nuclear magnetic resonance fits well into this classification. This technique has been used by others¹ and by us² to investigate electrolyte solutions and biological or model systems. We have been interested in the chemistry of cyclopolymethy-lenetetrazoles for some time.³ These compounds are characterized by their strong stimulating action on the central nervous system and, in     

Detailed comparison of the pnicogen bond with chalcogen,halogen, and hydrogen bonds

The characteristics of the pnicogen bond are explored using a variety of quantum chemical techniques. In particular, this interaction is compared with its halogen and chalcogen bond cousins, as well as with the more common H‐bond. In general, these bonds are all of comparable strength. More specifically, they are strengthened by the presence of an electronegative substituent on the electron‐acceptor atom, and each gains strength as one moves down the appropriate column of the periodic table, for example, from N to P to As. These noncovalent bonds owe their stability to a mixture in nearly equal parts of electrostatic attraction and charge transfer, along with a smaller dispersion component. The charge transfer arises from the overlap between the lone pair of the electron donor and a σ* antibond of the acceptor. The angular characteristics of the equilibrium geometry result primarily from a compromise between electrostatic and induction forces. Angular distortions of the H‐bond are typically less energetically demanding than comparable bends of the other noncovalent bonds. © 2012 Wiley Periodicals, Inc.