Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

scholarly journals Estudo do tautomerismo ceto-enólico da 7-epi-clusianona através de cálculos teóricos de deslocamentos químicos de RMN

2020 ◽  
Author(s):  
Ana Carolina Ferreira de Albuquerque ◽  
José Walkimar de Mesquita Carneiro ◽  
Fernando Martins dos Santos Junior
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectroscopic Techniques ◽  
Chemical Structures ◽  
Nmr Parameters

The properties of natural products, including their biological and pharmacological activities, are directly correlated with their chemical structures. Thus, a correct structural characterization of these compounds is a crucial step to the understanding of their biological activities. However, despite the recent advances in spectroscopic techniques, structural studies of natural products can be challenging. This way, theoretical calculations of Nuclear Magnetic Resonance (NMR) parameters (such as chemical shifts and coupling constants) have proven to be a powerful and low-cost tool for the aid to experimental techniques traditionally used for the structural characterization of natural products. One of the several applications of quantum-mechanical calculations of NMR parameters is the study of tautomerism. Since chemical shifts are sensitive to the tautomeric equilibrium, this technique can provide crucial informations. In this work, it was applied a protocol for theoretical calculations of ¹³C chemical shifts in order to study the tautomerism of the natural product 7-epi-clusianone, isolated from Rheedia gardneriana. This protocol consists in a Monte Carlo conformational search, followed by geometry optimization and shielding tensors calculations, both using a density functional level of theory. After comparison of theoretical and experimental data, it was possible to confirm the two tautomers present in equilibrium in the experimental solution. Furthermore, this study highlights how this theoretical protocol can be an effective method in identifying the preferred tautomeric form in solution.

Vinylsilylferrocenes and Ethynyl(vinyl)silylferrocenes. Synthesis, Multinuclear Magnetic Resonance Study and DFT Calculations

2014 ◽  
Vol 69 (6) ◽  
pp. 704-714 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Elena V. Klimkina
Keyword(s):  
Nmr Spectroscopy ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Magnetic Resonance Study ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Multinuclear Magnetic Resonance

Ferrocenylsilanes with various functions at silicon (chlorine, vinyl, ethynyl) were prepared and studied by multinuclear magnetic resonance methods (1H, 13C, 29Si NMR spectroscopy). The gasphase geometries of the silanes were optimized by calculations at the B3LYP=6-311+G(d,p) level of theory, and NMR parameters (chemical shifts δ13C, δ29Si, spin-spin coupling constants) were calculated at the same level of theory.

scholarly journals Computational NMR of Carbohydrates: Theoretical Background, Applications, and Perspectives

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2450
Author(s):  
Leonid B. Krivdin
Keyword(s):  
Chemical Shifts ◽  
Main Idea ◽  
Theoretical Background ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Huge Amount ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Developing Area ◽  
Spin Spin Coupling

This review is written amid a marked progress in the calculation of NMR parameters of carbohydrates substantiated by a vast amount of experimental data coming from several laboratories worldwide. By no means are we trying to cover in the present compilation a huge amount of all available data. The main idea of the present review was only to outline general trends and perspectives in this dynamically developing area on the background of a marked progress in theoretical and computational NMR. Presented material is arranged in three basic sections: (1)—a brief theoretical introduction; (2)—applications and perspectives in computational NMR of monosaccharides; and (3)—calculation of NMR chemical shifts and spin-spin coupling constants of di- and polysaccharides.

scholarly journals NMR parameters of FNNF as a test for coupled-cluster methods: CCSDT shielding and CC3 spin–spin coupling

2020 ◽  
Vol 22 (37) ◽  
pp. 21350-21359
Author(s):  
Michał Jaszuński ◽  
Stephan P. A. Sauer ◽  
Rasmus Faber ◽  
David J. D. Wilson
Keyword(s):  
Ab Initio ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupled Cluster ◽  
Nmr Parameters ◽  
Coupled Cluster Methods ◽  
Quantitative Accuracy ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Cluster Methods

NMR shielding and spin–spin coupling constants of cis and trans isomers of FNNF have been determined to near-quantitative accuracy from ab initio calculations.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

A Comparative Study of Metal Shielding in Low Valent Vanadium, Niobium and Manganese Complexes

1982 ◽  
Vol 37 (5) ◽  
pp. 631-645 ◽  
Author(s):  
Dieter Rehder ◽  
Hans-Christoph Bechthold ◽  
Ahmet Keçeci ◽  
Hartwig Schmidt ◽  
Michael Siewing
Keyword(s):  
Comparative Study ◽  
Nuclear Spin ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Manganese Complexes ◽  
Ligand Field ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Ligand Bond

Variations of the metal chemical shifts δ(51V), δ(55Mn) and δ(93Nb) with the paramagnetic deshielding contribution to the overall shielding are discussed in terms of influences imposed by the ligand field splitting, the nephelauxetic effect and the covalency of the metal-to-ligand bond. Complexes under investigation are isoelectronic and/or iso-structural series [M(CO)6-nLn]q (M = V, Nb: q = -1; M = Mn: q = + 1; n = 0-6), η5-C5H5M(CO)4-nLn (M = V, Nb; n = 0-4) and η5-C5H5M(L')2L (M = V, L' = NO; M = Mn, L' = CO). L is a monodentate or l/n oligodentate phosphine. η varies with the point symmetry of the complex, and with ligand parameters of primarily electronic or steric origin. Generally, for weak to medium π-interaction, there is a decrease of shielding with decreasing π-acceptor power of the ligand, increasing ligand bulkiness, increasing ring strains in chelate structures and increasing degree of substitution. For strong π-interaction, the trends may be interconverted. PF3 is shown to be a slightly weaker π-acceptor than CO. Selected results on nuclear-spin spin coupling constants, 13C and 31P shielding are also presented

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