Unravelling the kinetics and molecular mechanism of the degenerate Cope rearrangement of bullvalene

2020

The kinetics and molecular mechanism of the gas phase degenerate Cope rearrangement (DCR) of bullvalene have been investigated by applying quantum mechanical calculations. Highly accurate energies (CBS-QB3 and CBS-APNO) and RRKM calculations were employed to study the kinetics and ‘fall-off’ behavior. It was found that the DCR of bullvalene (C3v) occurs through a bishomoaromatic transition structure (C2v) with an energy barrier of ∼49 kJ mol−1. The calculated activation energy and enthalpy were in good agreement with the available values in the literature, but lower than those of common Cope rearrangement; this result is related to the high stabilization energy due to the interaction of the…

A molecular electron density theory (MEDT) study of the role of halogens (X2= F2, Cl2, Br2and I2) on the aza-Michael-addition reactions

2020

Using the Molecular Electron Density Theory (MEDT), a set of uncatalyzed and X2 molecule-catalyzed (X2 = F2, Cl2, Br2, or I2) aza Michael addition reactions (aza-MARs) between pyrrolidine (PYR) and methyl acrylate (MA) have been studied in the gas phase and in dichloromethane (DCM) medium from the kinetics and molecular mechanism aspects. Analysis of the conceptual DFT reactivity indices indicates that the coordination of the X2 molecules to the oxygen of the MA's carbonyl group increases both the softness and the electrophilic character of MA, thus explaining the catalytic role of the X2 molecules. The nucleophilic attack of the nitrogen of PYR on the MA's β conjugated carbon is the rate-d…

Calculation of the rate constants for hydrogen abstraction reactions by Hydroperoxyl radical from Methanol, and the investigation of stability of CH3…

2020

Abstract Master equation (ME) with Lennard-Jones potential utilized to simulate the collision between CH3OH and HO2 radical in the presence of bath gas. The reaction mechanism explored through the lowest doublet potential energy surface at CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory that is barrierless and forms shallow energized intermediate at the entrance channel. The investigation of the fractional population showed that lifetime of CH3OH.HO2 intermediate (INT*) is fairly short due to its shallow depth, and at the low temperature, most reaction takes place by re-dissociation back to reactants and also when the pressure is high enough, the INT* is thermalized and comes into eq…

Unraveling the kinetics and molecular mechanism of gas phase pyrolysis of cubane to [8]annulene

2020

The kinetic and electron density flows are studied theoretically for the gas phase pyrolysis of cubane via its cage opening to reach bicyclooctatriene and then thermal rearrangement of bicyclooctatriene to produce [8]annulene which is the experimentally observed major product. The observed kinetic data at the MN15-L/maug-cc-pVTZ level of theory were in good agreement with the experimental results as compared to the CBS-QB3 method. The cage opening and the thermal rearrangement steps at the experimentally employed temperature of 520 K were exergonic and exothermic. The atmospheric rate constants calculated by means of the RRKM theory show that the cage opening is the rate-determining step. T…

Atmospheric Oxidation Reactions of Methyl Salicylate as Green Leaf Volatiles by OH Radical: Theoretical Kinetics and Mechanism

2020

Quasi-RRHO approximation and DFT study for understanding the mechanism and kinetics of nitration reaction of benzonitrile with nitronium ion

2021

Abstract The nitration reaction of benzonitrile with nitronium cation, NO2+, has been studied within the Molecular Electron Density Theory at the MN15-L/aug-cc-pVTZ level of theory. For this electrophilic aromatic substitution (EAS) reaction, three regioisomeric reaction paths have been studied. Quasi-RRHO approximation was applied to consider the vibrational contribution to entropy and correct the Gibbs free energy profile of the reaction in the solvent phase. Benzonitrile is less nucleophilically activated than benzene due to the presence of the electron-withdrawing CN group the meta position is the more favorable reaction path of this EAS reaction. The analysis of ELF and AIM demonstrate…

Closer Investigation of the Kinetics and Mechanism of Spirovinylcyclopropyl Oxindole Reaction with 3Σ–g-O2 by Topological Approaches and Unraveling t…

2021

In this investigation at the MN15L/Def2-TZVP level of theory, we present computational evidence indicating that the reaction of 3Σ-g-O2 with spirovinylcyclopropyl oxindole (2) leads to a product called spiro-1,2-dioxolane (2) in its singlet state; this reaction occurs via a stepwise mechanism and its rate-determining step is catalyzed by iodine radicals, which promotes opening of the three-membered ring under dark conditions. The conversion of 2 to 1-benzylindoline-2,3-dione (3) and 2-vinyloxirane (4) takes place via a concerted and slightly asynchronous reaction. Both electron localization function and AIM topological analysis reveal that the step associated with the attack of the 3Σ-g-O2 …