The barrier and the potential-energy surface of the isomerization from aminoboranylidene (BNH2) to iminoborane (HBNH) have been studied using complete active space self-consistent field (CASSCF) with the 6-31 + G(d, p) basis set and higher-level energy methods. The rate constants of the isomerization reaction are reported by employing the direct ab initio dynamics method. The geometries of all the stationary points were optimized using the B3LYP and CCSD methods with the cc-pVTZ and cc-pVQZ basis sets. The information along the intrinsic reaction coordinate (IRC) was also calculated at the CASSCF/6-31 + G (d,p) level of theory. The energies were refined at the G3, G3MP2, G3MP2B3, CBS-Q, CBS-QB3, and two high-level (HL) methods based on the geometries optimized using CASSCF/6-31 + G(d,p). The rate constants were evaluated using conventional transition-state theory (TST), canonical variational transition-state theory (CVT), and canonical variational transition-state theory with small curvature tunneling correction (CVT/SCT) and conventional transition-state theory with Eckart tunneling correction (TST/Eckart). According to the calculated results, we conclude that the tunneling effect is very important to this isomerization reaction.
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http://dx.doi.org/10.1007/s00894-005-0017-7 | DOI Listing |
Molecules
January 2025
Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland.
This research investigates the mechanism of the cyanide-type umpolung reaction in benzoin condensation using topological analysis of ELF and catastrophe theory. The study achieves a comprehensive understanding of the evolution of chemical bonds and non-bonding electron density in the reaction of benzaldehyde and cyanide ions. The results reveal that the reaction proceeds through five transition state structures, with the formation of Lapworth's cyanohydrin being the rate-determining step.
View Article and Find Full Text PDFPhys Chem Chem Phys
January 2025
Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, Valladolid, Spain.
This article reports a theoretical study on the halogen exchange reactions YX + CHO → Y + XCHO (with Y = F, Cl, Br; X = Cl, Br, I) carried out at a high level of accuracy using coupled-cluster based methodologies including CCSD(T)-F12, CCSD(T)/CBS and CCSDT(Q). Most of the reactions are exothermic at room temperature, with the exception of the reactions FI + CHO → F + ICHO and ClI + CHO → Cl + ICHO. Exothermicity follows two concurrent trends established by the strength of the bonds being cleaved and formed: Y = F < Cl < Br (X-Y bond strength) and X = Cl > Br > I (C-X bond strength).
View Article and Find Full Text PDFFood Res Int
February 2025
College of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China; Engineering Research Center of Food Thermal-Processing Technology, Shanghai Ocean University, Shanghai 201306, China. Electronic address:
Ethylene oxide (EO) and propylene oxide (PO) are widely used as sterilizing agents in the food industry. However, their residues in food packaging can migrate into food and react with it, affecting the accuracy of residue detection in food. This study aims to explore the reaction mechanisms between EO and PO and aqueous food simulants using both experimental and computational methods.
View Article and Find Full Text PDFNat Commun
January 2025
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
The kinetics of dislocation reactions, such as dislocation multiplication, controls the plastic deformation in crystals beyond their elastic limit, therefore critical mechanisms in a number of applications in materials science. We present a series of large-scale molecular dynamics simulations that shows that one such type of reactions, the nucleation of dislocation at free surfaces, exhibit unconventional kinetics, including unexpectedly large nucleation rates under compression, very strong entropic stabilization under tension, as well as strong non-Arrhenius behavior. These unusual kinetics are quantitatively rationalized using a variational transition state theory approach coupled with an efficient numerical scheme for the estimation of vibrational entropy changes.
View Article and Find Full Text PDFACS Omega
January 2025
Laboratory of Theoretical Chemistry, Theoretical and Structural Physical Chemistry Unit, Namur Institute of Structured Matter (NISM), University of Namur, rue de Bruxelles, 61, B-5000 Namur, Belgium.
Density functional theory (DFT) has been enacted to study the Diels-Alder reaction between 2,5-dimethylfuran (2,5-DMF), a direct product of biomass transformation, and acrolein and to analyze its thermodynamics, kinetics, and mechanism when catalyzed by a Lewis acid (LA), in comparison to the uncatalyzed reaction. The uncatalyzed reaction occurs via a typical one-step asynchronous process, corresponding to a normal electron demand (NED) mechanism, where acrolein is an electrophile whereas 2,5-DMF is a nucleophile. The small endo selectivity in solvents of low dielectric constants is replaced by a small exo selectivity in solvents with larger dielectric constants, such as DMSO.
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