Additive Character of Electron Donation by Methyl Substituents within a Complete Series of Polymethylated [1-(η6-MenC6H6−n)-closo-1,2,3-FeC2B9H11] Complexes. Linear Correlations of the NMR Parameters and FeII/IIIRedox Potentials with the Number of Arene Methyls

2011 ◽  
Vol 50 (7) ◽  
pp. 3097-3102 ◽  
Author(s):  
Bohumil Štíbr ◽  
Mario Bakardjiev ◽  
Josef Holub ◽  
Aleš Růžička ◽  
Zdeňka Padělková ◽  
...  
Keyword(s):  
Additive Character ◽  
Nmr Parameters ◽  
Complete Series ◽  
Electron Donation ◽  
Linear Correlations

A non-invasive NMR and MRI method to analyze the rehydration of dried sea cucumber

2015 ◽  
Vol 7 (6) ◽  
pp. 2413-2419 ◽  
Author(s):  
Shaote Geng ◽  
Huihui Wang ◽  
Xiaoling Wang ◽  
Xiaojun Ma ◽  
Shan Xiao ◽  
...  
Keyword(s):  
Water Uptake ◽  
Sea Cucumber ◽  
Profile Analysis ◽  
Texture Profile Analysis ◽  
Sea Cucumbers ◽  
Texture Profile ◽  
Good Linear ◽  
Non Invasive ◽  
Nmr Parameters ◽  
Linear Correlations

NMR and MRI were employed to analyze the water uptake and distribution during rehydration processing of lightly dried sea cucumbers. Good linear correlations were observed between the NMR parameters and texture profile analysis.

scholarly journals Changes of humic acids structure on selected key monitoring localities of arable soils

2011 ◽  
Vol 48 (No. 1) ◽  
pp. 40-44 ◽  
Author(s):  
G. Barančíková
Keyword(s):  
Humic Acids ◽  
Elemental Analysis ◽  
Humus Content ◽  
Optical Parameter ◽  
Olefinic Carbon ◽  
Monitoring Period ◽  
Nmr Parameters ◽  
Carboxylic Groups ◽  
Linear Correlations ◽  
C Nmr

Soil fertility is largely determined by the content and quality of soil organic matter. SlovakRepublic monitoring system includes evaluation of soil humus content, basic humic parameters and also chemical structure of humic acids (HA). Changes in humic acids structure on five selected key localities during monitoring period (1994&ndash;2000) are presented in this study. Among soil types, essentially between Chernozem and Planosol, in elemental analysis, optical parameter and 13C NMR parameters significant differences determined by Student&rsquo;s test were observed (Tables 2 and 3). During monitoring period small oxidation trend mainly on Calcaric Fluvisol and Planosol HA expressed by increase of oxygen content and O/C, O/H ratio was observed. Oxidation trends during monitoring period confirm also position of Calcaric Fluvisol and Planosol HA on van Krevelen diagram. Changes in optical parameter E<sup>1%</sup><sub>6</sub>and content of carboxylic groups for the period of monitoring were negligible. Some changes throughout monitoring in <sup>13</sup>C NMR parameters were recorded. On all observed HA considerable decrease of carbon in region 106&ndash;143 ppm, characteristic for aromatic and olefinic carbon with C&ndash;C, C&ndash;H bond, was observed. Spectroscopic parameters are in good agreement with elemental analysis and carboxylic groups. Joint relationships between changes in determined parameters are expressed by significant linear correlations. Predominantly between parameters calculated from <sup>13</sup>C NMR spectra and data of elemental analysis and optical parameter E<sup>1%</sup><sub>6</sub>highly significant linear correlations (R &gt; 0.93) are found (Table 4).&nbsp;

The Synthesis of 10-Halo-Substituted Derivatives of nido-7,8,9-PC2B8H11 and [nido-7,8,9-PC2B8H10]- and New Linear Correlations Between NMR Parameters

2005 ◽  
Vol 70 (11) ◽  
pp. 1861-1872 ◽  
Author(s):  
Josef Holub ◽  
Mario Bakardjiev ◽  
Bohumil Štíbr
Keyword(s):  
Nmr Spectroscopy ◽  
Chemical Shifts ◽  
Proton Sponge ◽  
Nmr Chemical Shifts ◽  
Nmr Parameters ◽  
Neutral Compounds ◽  
Experimental Errors ◽  
Derivatives Of ◽  
Linear Correlations ◽  
Individual Cluster

Halogenation of the eleven-vertex phosphadicarbaborane nido-7,8,9-PC2B8H10 (1) with CCl4, Br2 or I2 in the presence of anhydrous AlCl3 (solvents CCl4, CS2, and benzene, respectively) generated a series of 10-X-nido-7,8,9-PC2B8H10 (10-X-1) compounds (X = Cl, Br, and I) in yields 55, 65, and 63%, respectively. Anionic compounds [10-X-nido-7,8,9-PC2B8H10]- (10-X-2) (X = Cl, Br, I) were obtained by treatment of the corresponding neutral compounds with "proton sponge" (PS = 1,8-bis(dimethylamino)naphthalene). All compounds were characterized by multinuclear (11B, 1H, and 31P) NMR spectroscopy and [11B-11B]-COSY and 1H-{11B(selective)} NMR measurements that led to complete assignments of all 11B and 1H resonances to individual cluster positions. Interesting halo-substitution NMR effects are also discussed in terms of new linear correlations. All the changes in NMR chemical shifts (∆) induced at the various skeletal sites by halogeno substituents on specific sites can be related to an arbitrary reference skeleton and are, within experimental errors, linearly proportional to those induced at the substituted site (∆α) of the reference skeleton.

Short Communication: A Note of Caution to Users of ECOSAR

1999 ◽  
Vol 34 (1) ◽  
pp. 179-182 ◽  
Author(s):  
Klaus L.E. Kaiser ◽  
John C. Dearden ◽  
Werner Klein ◽  
T. Wayne Schultz
Keyword(s):  
Environmental Protection Agency ◽  
Partition Coefficients ◽  
Short Communication ◽  
Computer Software ◽  
Aquatic Organisms ◽  
Protection Agency ◽  
Personal Computer Software ◽  
Linear Correlations ◽  
Class Representative ◽  
Chemical Class

Abstract ECOSAR (1998), a personal computer software program available from the U.S. Environmental Protection Agency (EPA) and affiliated vendors, is used to estimate the toxicity of chemicals to aquatic organisms, particularly fish, daphnid and algae species. It relies on approximately 150 equations, each for a chemical class of substances (Clements et al. 1996), which are linear correlations (SARs) of measured toxicity values of class-representative compounds with their octanol/water partition coefficients, with the latter taken from a database or computed by a companion program.

Conformational Stability, FMO, NMR, MEP and NBO Analysis of 2,5-Di-methyl-2,5-bis(methylthio)-1,4-dithiane and Dimethoxy compounds by DFT Approach

2021 ◽  
Vol 17 ◽  
Author(s):  
Nasrin Masnabadi
Keyword(s):  
Computational Methods ◽  
Electrostatic Potential ◽  
Conformational Stability ◽  
Nbo Analysis ◽  
Dft Methods ◽  
Geometrical Properties ◽  
Stereoelectronic Effect ◽  
Nmr Parameters ◽  
Electron Transfers ◽  
Stability Energy

Abstract: Conformational behaviors of 2,5-dimethoxy-2,5-dimethyl-1,4-dithiane (compound 1) and 2,5-dimethyl-2,5-bis (methylthio)-1,4-dithiane (compound 2) investigated by computational methods including B3LYP/6-311+G** and M06-2X/6-311+G** levels of theory and NBO analysis. The stereoelectronic effect of axial, axial (ax, ax) and equatorial, equa-torial (eq, eq) conformations were studied using NBO analysis. Using NBO analysis, the values of the stereoelectronic effects were calculated through the energy of stability associated with the electron transfers of compounds 1 and 2. The results showed that the eq, eq conformations of the studied compounds were more stable than their corresponding ax, ax conformations, and LP2X→σS1-C2 and LP2S→σ*C2-X electron transfers play important roles in the conformational be-havior of the studied compounds. The main purpose of the present work was to study the effects of stereoelectronic inter-actions and steric on the conformational superiority of the di-methoxy (compound 1) and di-thiomethyl compounds (com-pound 2). Thus, the values of resonance stability energy, non-diagonal elements, and orbital populations were investigated. Also, active electrophilic and nucleophilic centers were identified using fronting orbitals analysis obtained by DFT methods. The electrostatic potential maps of the title compounds were investigated at the B3LYP/6-311+G* level of theory. All of the NMR parameters and geometrical properties of both compounds were determined in this study.

scholarly journals Relativistic Effects on NMR Parameters of Halogen-Bonded Complexes

Molecules ◽  
2019 ◽  
Vol 24 (23) ◽  
pp. 4399 ◽  
Author(s):  
Ibon Alkorta ◽  
José Elguero ◽  
Manuel Yáñez ◽  
Otilia Mó ◽  
M. Merced Montero-Campillo
Keyword(s):  
Relativistic Effects ◽  
Lewis Base ◽  
Coupling Constants ◽  
Basic Site ◽  
Lewis Bases ◽  
Nmr Parameters ◽  
Quadrupolar Coupling ◽  
Binary Complexes ◽  
Computational Level ◽  
Bonded Complexes

Relativistic effects are found to be important for the estimation of NMR parameters in halogen-bonded complexes, mainly when they involve the heavier elements, iodine and astatine. A detailed study of 60 binary complexes formed between dihalogen molecules (XY with X, Y = F, Cl, Br, I and At) and four Lewis bases (NH3, H2O, PH3 and SH2) was carried out at the MP2/aug-cc-pVTZ/aug-cc-pVTZ-PP computational level to show the extent of these effects. The NMR parameters (shielding and nuclear quadrupolar coupling constants) were computed using the relativistic Hamiltonian ZORA and compared to the values obtained with a non-relativistic Hamiltonian. The results show a mixture of the importance of the relativistic corrections as both the size of the halogen atom and the proximity of this atom to the basic site of the Lewis base increase.

scholarly journals A Review on Combination of Ab Initio Molecular Dynamics and NMR Parameters Calculations

2021 ◽  
Vol 22 (9) ◽  
pp. 4378
Author(s):  
Anna Helena Mazurek ◽  
Łukasz Szeleszczuk ◽  
Dariusz Maciej Pisklak
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Small Amplitude ◽  
Ab Initio Molecular Dynamics ◽  
Quantum Mechanical ◽  
Time Step ◽  
Noticeable Effect ◽  
Nmr Parameters ◽  
Mechanical Methods ◽  
Simulation Time

This review focuses on a combination of ab initio molecular dynamics (aiMD) and NMR parameters calculations using quantum mechanical methods. The advantages of such an approach in comparison to the commonly applied computations for the structures optimized at 0 K are presented. This article was designed as a convenient overview of the applied parameters such as the aiMD type, DFT functional, time step, or total simulation time, as well as examples of previously studied systems. From the analysis of the published works describing the applications of such combinations, it was concluded that including fast, small-amplitude motions through aiMD has a noticeable effect on the accuracy of NMR parameters calculations.

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