scholarly journals Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

2017 ◽  
Vol 13 ◽  
pp. 410-416 ◽  
Author(s):  
Michael L McKee ◽  
Grzegorz Mlostoń ◽  
Katarzyna Urbaniak ◽  
Heinz Heimgartner
Keyword(s):  
Computational Methods ◽  
Computational Study ◽  
Heavy Atom ◽  
Ring Closure ◽  
Reactive Intermediate

An intriguing stepwise diradical mechanism of the dimerization of the reactive intermediate (thiocarbonyl S-methanide) appearing in the reaction of phenyl selenophen-2-yl thioketone with diazomethane was studied by means of computational methods. The preferred formation of the unusual macroheterocycle, competitive with the 1,3-ring closure leading to a thiirane and the head-to-head dimerization yielding a 1,4-dithiane derivative, respectively, was explained based on the analysis of the structure of the favored conformer of the intermediate, delocalized diradical species. The influence of selenium as a ‘heavy atom’ for stabilization of this intermediate has been emphasized.

Spin-forbidden heavy-atom tunneling in the ring-closure of triplet cyclopentane-1,3-diyl

2021 ◽  
Author(s):  
Luís P. Viegas ◽  
Cláudio Manaia Nunes ◽  
Rui Fausto
Keyword(s):  
Heavy Atom ◽  
Ring Closure ◽  
Quantum Mechanical ◽  
Quantum Mechanical Tunneling

In 1975, Buchwalter and Closs reported one of the first examples of heavy-atom quantum mechanical tunneling (QMT) by studying the ring closure of triplet cyclopentane-1,3-diyl to singlet bicyclo[2.1.0]pentane in cryogenic...

scholarly journals A computational study of the influence of methyl substituents on competitive ring closure to α- and β-lactones

2017 ◽  
Vol 15 (34) ◽  
pp. 7235-7240 ◽  
Author(s):  
Philippe B. Wilson ◽  
Ian H. Williams
Keyword(s):  
Computational Study ◽  
Ring Closure

gem-Dimethyl substitution at C3 enhances the preference for β-lactone formation from 2-chlorosuccinate but methylation at C2 almost favours α-lactone.

The effect of the aliphatic carboxylate linkers on the electronic structures, chemical bonding and optical properties of the uranium-based metal–organic frameworks

RSC Advances ◽  
2015 ◽  
Vol 5 (34) ◽  
pp. 26735-26748 ◽  
Author(s):  
Saumitra Saha ◽  
Udo Becker
Keyword(s):  
Optical Properties ◽  
Detailed Analysis ◽  
Computational Methods ◽  
Chemical Bonding ◽  
Electronic Structures ◽  
Computational Study ◽  
Metal Organic Frameworks ◽  
Metal Organic ◽  
First Time

A series of uranyl containing aliphatic dicarboxylate structures is studied using computational methods. Our computational study provides a detailed analysis of these MOFs and explores the effect of linkers on their properties for the first time.

scholarly journals Reductive activation and structural rearrangement in superoxide reductase: a combined infrared spectroscopic and computational study

2014 ◽  
Vol 16 (27) ◽  
pp. 14220-14230 ◽  
Author(s):  
M. Horch ◽  
A. F. Pinto ◽  
T. Utesch ◽  
M. A. Mroginski ◽  
C. V. Romão ◽  
...  
Keyword(s):  
Computational Methods ◽  
Structural Changes ◽  
Computational Study ◽  
Structural Rearrangement ◽  
Superoxide Reductase ◽  
Difference Spectroscopy ◽  
Combined Approach ◽  
Reductive Activation ◽  
Infrared Spectroscopic

Local and global structural changes that enable reductive activation of superoxide reductase are revealed by a combined approach of infrared difference spectroscopy and computational methods.

scholarly journals Should External Heavy-Atom Effects be Expected in Transition Metal Complexes?

2018 ◽  
Author(s):  
Justin Lomont ◽  
Son Nguyen ◽  
Charles Harris
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Spin State ◽  
Computational Study ◽  
Heavy Atom ◽  
Minimum Energy ◽  
Free Energy Barrier ◽  
Heavy Atom Effect ◽  
Atom Effect

Spin state changes frequently play a key role in the reactivity of transition metal complexes. The rates of spin-forbidden reactions are mediated both by the free energy barrier connecting reactants and products, as well as the strength of spin-orbit coupling (SOC) between the relevant electronic states. Since the 1950’s, there have been numerous demonstrations of external heavy-atom effects on organic molecules, in which a heavy atom, not chemically bonded to the molecule undergoing a change in spin state, perturbs the strength of SOC via an intermolecular effect. However, the potential role of external heavy atom effects on the rates of reactions involving transition metal complexes remains almost entirely unexplored. We report a computational investigation into the changes in SOC that occur along a bimolecular reaction coordinate when an incoming atom coordinates to the prototypical triplet reaction intermediate Fe(CO)4. The calculated changes in SOC are compared for molecules containing atoms ranging in atomic number from Z = 8 to Z = 53 approaching the Fe center (ZFe =26). No evidence for an external heavy atom effect was found, and the changes in SOC with the approach of each incoming group were similar in magnitude. In fact, when taking into account the different minimum energy crossing point geometries for the different incoming groups, the opposite of an external heavy atom effect trend is predicted for this reaction. The results of this computational study suggest that external heavy atom effects are unlikely to have a significant effect on the rates of spin-forbidden reactions for transition metal complexes. <br>

scholarly journals Isomerization and Fragmentation Reactions on the [C2SH4] Potential Energy Surface. The Metastable Thione-S-Methylide Isomer

2020 ◽  
Author(s):  
Zoi Salta ◽  
Marc E. Segovia ◽  
Aline Katz ◽  
Nicola Tasinato ◽  
Vincenzo Barone ◽  
...  
Keyword(s):  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Computational Study ◽  
Experimental Information ◽  
Reaction Scheme ◽  
Ring Closure ◽  
Complete Analysis

Thione S-methylide (TSM), the parent species of the thiocarbonyl ylide family, is a 1,3-dipolar, planar species on the [C2SH4] potential energy surface (PES), which has not shared the richness of studies dedicated to its isomers, the cyclic thiirane (THI), and the keto-enol pair vinyl thiol (VTH)/thioacetaldehyde (THA). While the conrotatory ring closure reaction toward THI was studied in the ‘90s, no complete analysis of the PES is available in the literature. In the present paper, we report a computational study of the reaction scheme linking all species on that PES. We employ several levels of calculation, ranging from density functional theory (DFT), through CCSD(T) based composite schemes, to CASSCF/CASPT2 multi-reference procedures, to find the best description of TSM, its isomers, and the transition states (TSs) ruling their interconversion. Fragmentation of TSM, THA and THI were investigated and compared to the available experimental information. We found that the B2PLYP-D3 functional, contrary to M06-2XD3 or B97X-D, describes well the geometry of both TSM and the transition state connecting it to THI. The reverse barrier, from THI to TSM, amounts to 52.2 kcal mol-1 (to be compared to 17.6 kcal mol-1 for the direct one), thus explaining why, in general, thiocarbonyl ylides cannot be prepared from thiiranes. Conversion of THI to VTH implies also a large barrier, explaining why the reaction has been observed only at high temperatures. The fragmentation of THI to S(3P) or S(1D) and ethylene was also explored, together with the decomposition to H2S plus acetylene. Open species, both in triplet and singlet states, were identified as intermediates in the fragmentations, and their energies were found to be lower than the transition state for the isomerization of THI to VTH, thus explaining the preference for fragmentation over isomerization at relatively low temperatures.

A vibrational spectroscopic and computational study of gaseous protonated and alkali metal cationized G–C base pairs

2020 ◽  
Vol 22 (20) ◽  
pp. 11546-11557 ◽  
Author(s):  
Ruodi Cheng ◽  
Jonathan Martens ◽  
Travis D. Fridgen
Keyword(s):  
Alkali Metal ◽  
Computational Methods ◽  
Computational Study ◽  
Base Pairs ◽  
Irmpd Spectroscopy ◽  
Structures And Properties

The structures and properties of metal cationized complexes of 9-ethylguanine (9eG) and 1-methylcytosine (1mC), (9eG:1mC)M+, where M+ = Li+, Na+, K+, Rb+, Cs+ as well as the protonated complex, (9eG:1mC)H+, have been studied using a combination of IRMPD spectroscopy and computational methods.

Application of boundary conditions “actuator disk” in computational study of aerodynamic interference of the engine and airframe of a passenger aircraft

2020 ◽  
Author(s):  
I.V. Voronich ◽  
V.H. Nguyen
Keyword(s):  
Power Plant ◽  
Computational Methods ◽  
Computational Study ◽  
Engine Performance ◽  
Aerodynamic Characteristics ◽  
Actuator Disk ◽  
Air Intake ◽  
Aerodynamic Interference ◽  
Passenger Aircraft ◽  
The Impact

Computational methods for obtaining aerodynamic characteristics of an aircraft are currently a source which supplements the data of aerodynamic experiment. This applies to the improvement of local aerodynamics, as well as the impact of the power plant on the flow around the airframe and aerodynamic characteristics of the aircraft. Despite the development of computational methods and computer technology, the tasks of integrating the power plant impose requirements for the refinement of the computational model, which are not fully implementable within the design cycle. However, simpler models can be potentially improved for situations of moderate aerodynamic interference by taking into account the profiles of variables in the air intake formed when the fan is in the nacelle. The paper considers the application of variants of the boundary condition “actuator disk” in the computational study of the contribution of the working power plant to the aerodynamic characteristics of the configuration. The approach is reliable for solving problems of weak and moderate aerodynamic interference. Engine performance has a weak effect on the overall aerodynamic characteristics at small angles of attack, but the component contributions caused by this factor are noticeable and have a different sign, which indicates the need to analyze this interaction.

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