The Origin of the Unusual C4ν Structure Predicted for SH4

1994 ◽  
Vol 47 (8) ◽  
pp. 1431 ◽  
Author(s):  
CJ Marsden ◽  
BA Smart
Keyword(s):  
Carbon Atom ◽  
Theoretical Calculations ◽  
Structural Parameters ◽  
Binding Energies ◽  
Molecular Orbital Calculations ◽  
Electrostatic Model ◽  
Net Charge ◽  
Methyl Group ◽  
Steric Factors ◽  
Net Charges

Ab initio molecular orbital calculations have been performed on C2v and C4v isomers of SH4, SF4 and S(CH3)4 to investigate the origin of the different structures adopted by these molecules. We propose an electrostatic model similar in spirit to the VSEPR approach; this implies that the net charges on the ligands L in SL4 compounds can control the geometry of these compounds. Steric factors may also be significant. Even though the net charges on hydrogen and on the CH3 group are similar when these act as ligands towards sulfur, the carbon atom in the methyl group bears a substantial negative net charge, which has important structural consequences. Binding energies and structural parameters are presented for SH4 which are obtained from more complete theoretical calculations than those previously reported.

scholarly journals Boron from net charge acceptor to donor and its effect on hydrogen uptake by novel Mg-B-electrochemically synthesized reduced graphene oxide

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Marla V. V. Satya Aditya ◽  
Srikanta Panda ◽  
Sankara Sarma V. Tatiparti
Keyword(s):  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Incubation Time ◽  
Photoelectron Spectroscopy ◽  
Weight Ratio ◽  
Hydrogen Uptake ◽  
Binding Energies ◽  
Unit Cell ◽  
Net Charge ◽  
Reduced Graphene

AbstractHydrogen uptake (H-uptake) is studied in ball milled Mg-B-electrochemically synthesized reduced graphene oxide (erGO) nanocomposites at PH2 ≈ 15 bar, ~ 320 °C. B/C (weight ratio): 0, ~ 0.09, ~ 0.36, ~ 0.90 are synthesized maintaining erGO≈10wt %. B occupies octahedral interstices within Mg unit cell—revealed by electron density maps. Persistent charge donations from Mg and B to C appear as Mg-C (~ 283.2 eV), B-C (~ 283.3–283.9 eV) interactions in C-1s core X-ray photoelectron spectroscopy (XPS) at all B/C. At B/C > 0.09, charge reception by B from Mg yields Mg-B interaction. This net charge acceptor role of B renders it electron-rich and does not alter Mg unit cell size significantly. Despite charge donation to both C and B, the Mg charge is <  + 2, resulting in long incubation times (> 5 h) at B/C > 0.09. At B/C≈0.09 the minimal Mg-B interaction renders B a charge donor, resulting in Mg-B repulsion and Mg unit cell expansion. Mg-C peak shift to lower binding energies (C-1s XPS), decreases incubation time to ~ 2.25 h and enhances H-uptake kinetics. Various atomic interactions influence the reduction of incubation time in H-uptake and increase its kinetics in the order: (Mg → C; B → C)B/C≈0.09, B: donor > (Mg → C)B/C=0 > (ternary Mg → B → C)B/C>0.09, B: acceptor.

Effect of delocalization of nonbonding electron density on the stability of the M–Ccarbene bond in main group metal-imidazol-2-ylidene complexes: a computational and structural database study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Samuel Tetteh ◽  
Albert Ofori
Keyword(s):  
Electron Density ◽  
Lone Pair ◽  
Main Group ◽  
Binding Energies ◽  
Electrostatic Model ◽  
Group Metal ◽  
Main Group Metal ◽  
Structural Database ◽  
The Stability ◽  
Lone Pair Electrons

Abstract The M–Ccarbene bond in metal (M) complexes involving the imidazol-2-ylidene (Im) ligand has largely been described using the σ-donor only model with donation of σ electrons from the sp-hybridized orbital of the carbene carbon into vacant orbitals on the metal centre. Analyses of the M–Ccarbene bond in a series of group IA, IIA and IIIA main group metal complexes show that the M-Im interactions are mostly electrostatic with the M–Ccarbene bond distances greater than the sum of the respective covalent radii. Estimation of the binding energies of a series of metal hydride/fluoride/chloride imidazol-2-ylidene complexes revealed that the stability of the M–Ccarbene bond in these complexes is not always commensurate with the σ-only electrostatic model. Further natural bond orbital (NBO) analyses at the DFT/B3LYP level of theory revealed substantial covalency in the M–Ccarbene bond with minor delocalization of electron density from the lone pair electrons on the halide ligands into antibonding molecular orbitals on the Im ligand. Calculation of the thermodynamic stability of the M–Ccarbene bond showed that these interactions are mostly endothermic in the gas phase with reduced entropies giving an overall ΔG > 0.

The 3-D Numerical Simulation of Heat Transfer Process of Finned Copper Tube

2011 ◽  
Vol 393-395 ◽  
pp. 412-415
Author(s):  
Jian Hua Zhong ◽  
Li Ming Jiang ◽  
Kai Feng
Keyword(s):  
Heat Transfer ◽  
Transfer Process ◽  
Theoretical Calculations ◽  
Structural Parameters ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Finned Tube ◽  
Copper Tube ◽  
Central Air Conditioning ◽  
Fin Thickness

In this article, finned copper tube used in the central air conditioning was acted as the discussed object. According to the combination with actual processing and theoretical calculations, Five finned tube was selected with typical structural parameters, and established their entity model using Pro/E, then the heat transfer process of finned tube was simulated through the ANSYS, the effect of the fin height, fin thickness and other structure parameters to the heat transfer enhancement of finned tube was researched. Meantime the efficiency of the heat transfer under different convection heat transfer coefficient was also studied.

The biosynthesis of ephedrine

1989 ◽  
Vol 67 (6) ◽  
pp. 998-1009 ◽  
Author(s):  
Gunnar Grue-Sørensen ◽  
Ian D. Spenser
Keyword(s):  
Carbon Atom ◽  
Benzoic Acid ◽  
Pyruvic Acid ◽  
Nmr Spectra ◽  
Carbon Skeleton ◽  
Resonance Spectroscopy ◽  
Methyl Group ◽  
Acid Incorporation ◽  
Group A ◽  
C Nmr

It is shown by 13C nuclear magnetic resonance spectroscopy that the labelled C2 fragment of [2,3-13C2]pyruvic acid is transferred intact into the C-methyl group and the adjacent carbon atom of the Ephedra alkaloids, norephedrine, ephedrine, norpseudoephedrine, and pseudoephedrine, in growing plants of Ephedragerardiana. This finding serves to identify pyruvate as the elusive precursor of the aliphatic C2 terminus of the skeleton of the alkaloids. In earlier experiments with C-labelled substrates, label from [3-14C]pyruvic acid was incorporated mainly, but not exclusively, into the C-methyl group of ephedrine, and label from [2-14C]pyruvate was incorporated similarly into the carbon atom adjacent to the C-methyl group. A C6–C1 unit related to benzaldehyde or benzoic acid has long been known to generate the benzylic fragment of the carbon skeleton of the Ephedra alkaloids. It is likely that the carbon skeleton of ephedrine is generated from pyruvate and either benzaldehyde or benzoic acid, by a reaction analogous to the formation of acetoin or diacetyl from pyruvate and acetaldehyde or acetic acid, respectively. Keywords: biosynthesis of ephedrine, Ephedra alkaloids, 13C NMR spectra, ephedrine, biosynthesis of pyruvic acid, incorporation into ephedrine13C NMR spectra.

Net charges and valence AO's in the methylamines; the hydrogen basis set and the properties of nitrogen

1985 ◽  
Vol 63 (7) ◽  
pp. 1487-1491 ◽  
Author(s):  
Giuseppe Del Re ◽  
Sándor Fliszár ◽  
Michel Comeau ◽  
Claude Mijoule
Keyword(s):  
Basis Set ◽  
Basis Sets ◽  
Methyl Groups ◽  
Extended Form ◽  
Amine Nitrogen ◽  
Methyl Group ◽  
Net Charges ◽  
Extended Basis

Net charges and valence AO's for ammonia, methylamine, dimethylamine, and trimethylamine were calculated using extended basis sets. Superposition effects, evaluated by replacing Pople's standard 6-31G* basis by an extended form in which the basis of the ammonia H atoms and of the methyl groups of trimethylamine are retained in the treatment of each molecule, indicate that the quality of the treatment of amine nitrogen atoms is strongly dependent on the number of methyl groups. A new, augmented basis is proposed for the hydrogens, which appears to be reasonably well balanced: comparison with familiar (e.g., 6-31G*) calculations illustrates in what manner the treatment of nitrogen is worsened when even just one methyl group is replaced by hydrogen unless the impoverishment of the basis is suitably taken care of.

A Probabilistic High-Pressure Zone Model of Dynamic Ice Structure Interactions and Associated Ice-Induced Vibrations

2021 ◽  
Author(s):  
Ridwan Hossain ◽  
Rocky Taylor ◽  
Lorenzo Moro
Keyword(s):  
High Pressure ◽  
Theoretical Calculations ◽  
Structural Parameters ◽  
Structural Response ◽  
Zone Model ◽  
Modelling Framework ◽  
Lower Amplitude ◽  
Average Strain Rate ◽  
High Pressure Zone ◽  
Lock In

Abstract During ice-structure interactions that are dominated by ice compressive failure, the majority of the ice loads are transmitted through localized contact regions known as high-pressure zones (hpzs). This paper presents a probabilistic modelling framework for dynamic ice-structure interaction based on the mechanics of hpzs. Individual hpzs are modelled as a nonlinear spring-damper system where the stiffness is modelled as a function of nominal strain, with the degree of softening depending on the average strain-rate. Both spalling and crushing failure mechanisms were assessed in the context of periodical sinusoidal response. For spall dominated failure, the model structure showed presence of frequency lock-in in the speed range of 100–125mm/s, beyond which the failure was found to be random in nature with lower amplitude of structural response. The amplitude was also found to be significantly influenced by structural parameters with structural damping having the highest contribution. For pure crushing, an estimated equilibrium layer thickness based on theoretical calculations also showed presence of frequency lock-in. The work highlights the importance of understanding the interplay between these mechanisms, as well as the role of ice conditions and structural parameters on the processes that dominate an interaction.

scholarly journals Flat Crown Ethers with Planar Tetracoordinate Carbon Atoms

2020 ◽  
Author(s):  
Venkatesan Thimmakondu ◽  
Krishnan Thirumoorthy
Keyword(s):  
Carbon Atom ◽  
Crown Ether ◽  
Crown Ethers ◽  
In Silico ◽  
Alkaline Earth ◽  
Experimental Studies ◽  
Building Blocks ◽  
Binding Energies ◽  
High Symmetry ◽  
Structural Rigidity

Novel flat crown ether molecules have been characterized in silico using DFT hybrid and hybrid-meta functionals. Monomer units of Si2C3 with a planar tetracoordinate carbon atom have been used as building blocks. Alkali (Li+, Na+, K+, Rb+, and Cs+) and alkaline-earth (Ca2+, Sr2+, and Ba2+) metals, and uranyl (UO2+ 2 ) ion selective complexes have also been theoretically identified. The high symmetry and higher structural rigidity of the host molecules may likely to impart higher selectivity in chelation. Theoretical binding energies have been computed and experimental studies are invited.

A STUDY OF THE STRUCTURES AND VIBRATIONAL SPECTRA OF THE N2O⋯(HX)2 AND ON2⋯(HX)2 WITH X = F, Cl, Br AND CN

2013 ◽  
Vol 12 (05) ◽  
pp. 1350044 ◽  
Author(s):  
NATHÁLIA B. D. LIMA ◽  
MÁRCIA K. D. L. BELARMINO
Keyword(s):  
Nitrous Oxide ◽  
Vibrational Spectra ◽  
Theoretical Calculations ◽  
Bond Formation ◽  
Binding Energies ◽  
Vibrational Modes ◽  
Out Of Plane ◽  
Usual Behavior ◽  
Bending Modes ◽  
Stable Structures

Theoretical calculations 6-311++G(d,p) have been performed in order to obtain binding energies and molecular properties of complexes involving nitrous oxide ( N2O ) and two HX (X = F, Cl, Br and CN ) molecules. Our calculations have revealed the existence of eleven stable structures. The vibrational changes which take place in the HX acid after complexation follow the usual behavior: the HX stretching frequency is shifted downward whereas its IR intensity is much enhanced. The new vibrational modes arising upon H-bond formation, were verified, especially, those associated with the out-of-plane and in-plane HX bending modes, which are pure rotations in the HX isolated molecule.

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