scholarly journals Kinetic and products of C3H3 and C4H2 reaction: theoretical and computational study

2018 ◽  
Vol 10 (2) ◽  
pp. 102
Author(s):  
Antonius Indarto
Keyword(s):  
Ab Initio ◽  
Master Equation ◽  
Reaction Kinetic ◽  
Computational Study ◽  
Molecular Structures ◽  
Computational Method ◽  
Propargyl Radical ◽  
Ring Molecules ◽  
Hydrocarbon Molecules ◽  
High Concentrations

The formation of first aromatic ring was suggested to be a crucial step of the PAHs and soot growth mechanism. In general, four-, five-, six-, or seven-membered ring molecules could be formed by the addition reaction of two hydrocarbon molecules resulted from many different pathways. Small hydrocarbon molecules with numerous concentrations during combustion/pyrolysis are suspected to play an important role. Propargyl radical (•C3H3) and butadiene (C4H2) have been chosen as the initial reactants in this discussion, since they are found at relatively high concentrations in flame experiments to examine the above particular reaction. Following initial addition mechanisms, their adduct intermediate can form a ring molecule and undergo subsequent rearrangement. All possible molecular structures were considered and the viability of each channel was assessed through a “RRKM + master equation” kinetic study. This study is an attemp and example to develop and apply molecular computational method for solving problems in the chemical engineering.Keywords: reaction kinetic, ab-initio calculation, RRKM theory, unimolecular reaction, propargyl, butadiene.AbstrakReaksi pembentukan cincin aromatic pada senyawa hidrokarbon merupakan mekanisme awal terpenting dari pembentukan Polisiklik Aromatik Hidrokarbon (PAH) dan jelaga karbon. Secara umum, senyawa hidrokarbon dengan cincin berjumlah empat, lima, enam, atau tujuh dapat dibentuk oleh reaksi gabungan dua molekul hidrokarbon. Molekul hidrokarbon dengan jumlah atom karbon rendah akan memainkan peranan penting ditinjau dari besarnya konsentrasi senyawa ini saat pembakaran/pirolisis. Dalam diskusi ini, reaksi propargil radikal (•C3H3) dan butadiena (C4H2) digunakan sebagai studi kasus karena konsentrasinya yang relatif tinggi dalam percobaan laboratorium dengan menggunakan bunsen. Secara garis besar, reaksi pembentukan rantai lingkar (cincin) dapat tercapai baik secara langsung setelah reaksi adisi atau melalui penataan ulang molekul. Berbagai struktur molekul dan mekanisme yang mungkin ada dalam reaksi ini akan dianalisis melalui studi kinetika "RRKM + persamaan master (master equation)". Studi ini juga ditujukan sebagai usaha dan contoh untuk memperkenalkan penggunaan kimia komputasi molekuler dalam menyelesaikan berbagai problem di bidang teknik kimia.Kata kunci: kinetika reaksi, perhitungan ab-initio, teori RRKM, reaksi unimolekular, propargil, butadiena.

scholarly journals Ab-Initio Computational Study : The Activation Energy Changes and Steric Effects In Peptide Synthesis Of Ac-AA-NH2 and Ac-AP-NH2

Molekul ◽  
2021 ◽  
Vol 16 (2) ◽  
pp. 137
Author(s):  
Indah Pratiwi ◽  
Bambang Cahyono ◽  
Parsaoran Siahaan
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Ab Initio ◽  
Peptide Synthesis ◽  
Reaction Mechanisms ◽  
Steric Effect ◽  
Computational Study ◽  
Computational Method ◽  
Side Chain ◽  
Concerted Reaction

Ab-Initio computational method can be used for simulating reaction mechanisms, such as concerted reaction mechanism on peptide synthesis. The concerted reaction is one of many possible pathways on how peptide can be synthesized. The purpose of this study are probing the concerted reaction mechanism and comparing the steric effect to the reaction, given by different side-chain of alanine (A) and proline (P). Two dipeptides formed from alanine and proline were computed at HF-SCF/6-31G** theory level: Ac-AA-NH2 and Ac-AP-NH2. The res.lts show the activation energy of Ac-AA-NH2  and Ac-AP-NH2 forming via concerted pathway are 167.541 kJ/mol and 161.044 kJ/mol, respectively. The steric difference in side-chain affects the dihedral angle of the structure, and also gives difference to the entropy value of reaction.

Ion solvation by dipolar aprotic solvents. An ab initio study

1987 ◽  
Vol 52 (1) ◽  
pp. 6-13 ◽  
Author(s):  
Petr Kyselka ◽  
Zdeněk Havlas ◽  
Ivo Sláma
Keyword(s):  
Ab Initio ◽  
Geometry Optimization ◽  
Molecular Structures ◽  
Dimethyl Sulphoxide ◽  
Ion Solvation ◽  
Interaction Energies ◽  
Ab Initio Study ◽  
Solvation Energies ◽  
Dipolar Aprotic Solvents ◽  
Complete Geometry Optimization

The paper deals with the solvation of Li+, Be2+, Na+, Mg2+, and Al3+ ions in dimethyl sulphoxide, dimethylformamide, acetonitrile, and water. The ab initio quantum chemical method was used to calculate the solvation energies, molecular structures, and charge distributions for the complexes water···ion, acetonitrile···ion, dimethyl sulphoxide···ion, and dimethylformamide···ion. The interaction energies were corrected for the superposition error. Complete geometry optimization was performed for the complex water···ion. Some generalizations are made on the basis of the results obtained.

scholarly journals Density Functional Theory and Complete Basis Set Ab Initio Computational Study of Five-, Six-, Seven- and Eight-hydrogen Coordinated Carbon Cations

1999 ◽  
Vol 23 (8) ◽  
pp. 502-503
Author(s):  
Branko S. Jursic
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computational Study ◽  
Basis Set ◽  
Functional Theory ◽  
Complete Basis ◽  
Complete Basis Set ◽  
High Level

High level ab initio and density functional theory studies are performed on highly protonated methane species.

scholarly journals Photoprotective Properties of Eumelanin: Computational Insights into the Photophysics of a Catechol:Quinone Heterodimer Model System

Photochem ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 26-37
Author(s):  
Victoria C. Frederick ◽  
Thomas A. Ashy ◽  
Barbara Marchetti ◽  
Michael N. R. Ashfold ◽  
Tolga N. V. Karsili
Keyword(s):  
Ground State ◽  
Sandwich Structure ◽  
Computational Study ◽  
Minimum Energy ◽  
Carbonyl Oxygen ◽  
Model System ◽  
Molecular Structures ◽  
Uv Damage ◽  
Chromosomal Dna ◽  
Relevant Model

Melanins are skin-centered molecular structures that block harmful UV radiation from the sun and help protect chromosomal DNA from UV damage. Understanding the photodynamics of the chromophores that make up eumelanin is therefore paramount. This manuscript presents a multi-reference computational study of the mechanisms responsible for the experimentally observed photostability of a melanin-relevant model heterodimer comprising a catechol (C)–benzoquinone (Q) pair. The present results validate a recently proposed photoinduced intermolecular transfer of an H atom from an OH moiety of C to a carbonyl-oxygen atom of the Q. Photoexcitation of the ground state C:Q heterodimer (which has a π-stacked “sandwich” structure) results in population of a locally excited ππ* state (on Q), which develops increasing charge-transfer (biradical) character as it evolves to a “hinged” minimum energy geometry and drives proton transfer (i.e., net H atom transfer) from C to Q. The study provides further insights into excited state decay mechanisms that could contribute to the photostability afforded by the bulk polymeric structure of eumelanin.

Ab Initio Computational Study of the Allenyl Cope Rearrangement ofsyn-7-Allenylnorbornene

1999 ◽  
Vol 121 (51) ◽  
pp. 12029-12034 ◽  
Author(s):  
James A. Duncan ◽  
Joseph K. Azar ◽  
J. Callan Beathe ◽  
Scott R. Kennedy ◽  
Carolyn M. Wulf
Keyword(s):  
Ab Initio ◽  
Computational Study ◽  
Cope Rearrangement

scholarly journals On local aromaticity of selected model aza-[n]circulenes (n = 6, 7, 8 and 9): Density functional theoretical study

2019 ◽  
Vol 12 (1) ◽  
pp. 70-81
Author(s):  
Denisa Cagardová ◽  
Vladimír Lukeš ◽  
Ján Matúška ◽  
Peter Poliak
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Molecular Structures ◽  
Functional Theory ◽  
Structure Of Molecules ◽  
Planar Molecules ◽  
P Type ◽  
Structural Indices ◽  
Lowest Unoccupied Molecular Orbitals ◽  
Local Aromaticity

Abstract A computational study using density functional theory is reported for selected model aza[n]circulenes (n = 6, 7, 8 and 9) and their derivatives consisting of pyrrole and benzene units. Local aromaticity of central rings was discussed and analyzed using theoretical structural indices. Depending on their molecular structures, energies of the highest occupied and lowest unoccupied molecular orbitals change from –5.23 eV to –4.08 eV and from –1.97 eV to –0.41 eV, respectively. Based on B3LYP calculated optimal geometries, electronic structure of molecules and their charge transport properties resulted in the suggestion of three planar molecules containing three or four pyrrole units as potential candidates for p-type semiconductors. Hole drift mobilities for ideal stacked dimers of these potential semiconductors were calculated and they range from 0.94 cm2·V−1·s−1 to 7.33 cm2·V−1·s−1.

ab initio MO Optimization of Molecular Structures of Fluoro- and Chloro-Substituted Dibenzo-p-dioxines and the Effect of Halogen Substitution at the 2,3,7,8-Positions on Metabolic Attack

1997 ◽  
Vol 52 (11) ◽  
pp. 1418-1431 ◽  
Author(s):  
Roland Weber ◽  
Till Kühn ◽  
Hanspaul Hagenmaier ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Energy Gap ◽  
Substituent Effects ◽  
Molecular Structures ◽  
X Ray ◽  
Degree Pattern ◽  
Chlorine Substituent ◽  
Homo Lumo ◽  
Good Agreement

Full ab initio optimizations were performed on the molecular structures of 24 fluorinated and chlorinated dibenzodioxines (PFDD/PCDD ) and dibenzofurans (PFDF/PCDF). Reasonable agreement was found by comparing the geometries of four calculated structures with known X-ray data from the literature. For the fluorine substituent, calculated electron densities (Mulliken total charges and π-electron charges) clearly demonstrate the opposite influence of the inductive (I) and mesomeric (M) effect. The changes in π-densities at carbons in ortho-, meta- and para-position are constant for each fluorine substituent (independent of degree, pattern, and position of substitution). It is thus possible to calculate the π-densities of the substituted dioxines by increments starting from dibenzodioxine. π-Charges from quantum mechanical calculations and the increment system show good agreement even for OctaFDD (O8FDD ), where eight substituent effects are acting additively. Compared with fluorine, the chlorine substituent exercises a smaller -I-effect and a clearly weaker +M-effect. The HOMO coefficients of the unsubstituted dibenzodioxine and dibenzofuran, extracted from ab initio calculations, yield a good explanation for the observed regioselective metabolic attack at the 2,3,7,8-positions. The squares of the HOMO-coefficients of the 2,3,7,8-positions in dibenzodioxine (DD ) are about ten times greater than those of the 1,4,6,9-positions. These HOMO coefficients are practically unaffected by halide substitution. But halogen substitution reduces strongly the electron density at the halogen-bound carbon, which, however, is a necessary prerequisite for the electrophilic oxygen transfer during metabolism. One would therefore expect halogen substitution of dibenzodioxine and dibenzofuran (DF) at the 2,3,7,8-position to hinder metabolism, as is indeed found. This provides a plausible explanation for the highly selective tissue retention of 2,3,7,8-substituted PCDDs and PCDFs. Our ab initio calculations of five tetra CDDs (T4CDDs) confirm the postulate of Kobayashi et al. [1 ] who, using semiempirical calculations, found a correlation between the toxicity of a dioxine congener and its absolute molecular hardness. The 2,3,7,8-T4CDD also exhibits the smallest absolute hardness (derived from the HOMO-LUMO energy gap) in our calculations.

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