Progress in Reaction Kinetics and Mechanism

Kinetics of the isomerisation and unimolecular degradation of n-octyl radicals have been studied with the reaction class transition state theory (RC-TST) method. To explore the kinetics of the 1,7-H migration reactions family, the accurate high-pressure limits of the rate constants for the reference reaction of this class (1-heptyl → 1-heptyl) have been calculated. Finally, both the achievements reported in this paper and previous developments are employed to obtain theoretical branching ratios of intramolecular H-transfers and unimolecular degradations of all possible n-octyl radicals; the results are in satisfactory agreement when compared to experiment. The application of the rates obtained to the simulation of a simple reactor is also reported.

Dual-level electronic structure calculation has been performed to investigate the mechanism and all possible channels of OH radical reaction with CH₃CH₂F. Geometries and frequencies are computed at the B3LYP/6-311G(d,p) level of theory for all stationary points and complexes and transition states are located. Potential energy surfaces are constructed at the PMP2/cc-pVTZ//B3LYP/6-311G(d,p) level + ZPE correction. Four types of reaction channels are identified: hydrogen abstraction, fluorine abstraction and attack on carbon atom along or perpendicular to the C–C bond axis. Hydrogen abstraction channels have lower barriers and are more exothermic, while out-of-plane β–H abstraction with the lowest barrier is competitive with a–H abstraction. Due to the high energy barrier, contributions of non-H abstraction channels are excluded. The influence of hydrogen bonding interaction is clearly observed in the barrier heights.

Stochastic simulation is carried out to investigate intracellular viral reaction kinetics and the time evolution of the average particle number (N̄) and coefficient variation (CV) for genome, template, and structural protein. The coefficient variation of these components is found to be ordered as: CV_template > CV_{structural protein} > CV_genome. The average particle number is also calculated via a deterministic approach. The magnitude value of the difference between the stochastic and deterministic approaches is found to be N̄ _template ≈ N̄ _{structural protein} > N̄ _genome. The Poisson algorithm has been used to investigate the number of particles in the dynamics of intracellular viral reaction kinetics. Our results show that the average particle number (N̄) obtained using the Poisson algorithm for both dynamics and stationary states is le ss than that obtained using the mean field approach relative to the quantity (N) found via the Gillespie algorithm. Also, the standard deviation of N̄ calculated via the Poisson algorithm is more than that obtained via the Gillespie algorithm. The equilibrium time for the population of particles via the Poisson algorithm is less than that via the Gillespie algorithm and the mean field approach. In the present study, the Gillespie algorithm is more reliable than the Poisson algorithm.

The effect of solvent on the rate constant of the reaction of nitrite ion with o-quinone has been investigated by means of voltammetry and voltammogram digital simulation methods. The experimental results have been compared with theoretical calculations; the latter results are in good agreement with experimental data and confirm that the dielectric constant of the solvent is the most influential factor on the rate of reaction.

Au nanoparticles have been found to possess high reactivity to convert NO into N₂O with both high conversion efficiency and selectivity. We have carried out DFT calculations on the reaction mechanism in the reduction of NO to N₂O by H₂ on the surface of Au₄⁺ and Au₄ nanoparticles. The results show that the catalytic cycle proceeds via complexes of Au–H with NO and involves two sequential elementary steps: the rupture of the H–H bond in H₂ and the formation of H₂O and N₂O molecules. On the basis of the calculated potential energy surface profiles, the reaction mediated by cationic nanoparticles is energetically more favourable compared to the neutral cluster, indicating that the activity of Au nanoparticles towards NO reduction is attributable to the concentration of positive charges on the nanoparticles.

In order to develop a general kinetic equation for the ultrasonic degradation of polymers, the general applicability of the common kinetic equations is discussed. The common ultrasonic-kinetic equations for polymers are used to fit original data collected from all available literature (over 366 experimental data points). The fitting accuracy of the kinetic equation is evaluated by the residual standard deviation. The fitting results indicate that the first-order equation and second-order equations are the most accurate and can replace other kinetic equations. Based on this, a general kinetic equation for the ultrasonic degradation of polymers is proposed, − d M t d t = k ( M t − M lim ) n where n = 1 or 2, i.e. when n = 1, it becomes a first-order dynamic equation; when n = 2, it is a second-order dynamic equation.

Structural and kinetic aspects of the retro-cheletropic ene reactions of N-phenyl-1-methyl-6-methylenecyclohexa-2,4-dienylmethanimine (R) and its deuterated derivative were investigated using a variety of computational methods. Theoretical calculations were carried out with DFT methods at the B3LYP and M06 levels of theory, using the 6-311++G(d,p) basis set. Vibrational frequency analysis confirmed the stationary states including the transition state (TSs) structures. The mechanistic studies on the retro-cheletropic ene processes rejected the stepwise mechanism and confirmed a five-membered cyclic TS for the reaction. The conversion of the reactant to the products proceeds through an asynchronous concerted mechanism. Theoretical calculations indicate that the reaction displays a primary kinetic isotope effect of 8.75 at 417 K. Calculated activation parameters, especially M06 results, are in good agreement with the experimental data. The natures of bond making and breaking during the reactions have been investigated using the concepts of donor–acceptor, electron charge density and Laplacian in NBO and AIM methods, respectively.

We have investigated the effects of O₂, ethanol, and KI on the photocatalytic efficiency of Bi₂Fe₄O₉ nanoparticles towards the degradation of methylene blue (MB). It is observed that O₂ has a negligible effect on the photocatalytic degradation rate of the dye, whereas ethanol and KI exhibit a strong suppression of the dye degradation, with a stronger effect observed for the latter. Hydroxyl radicals are shown, by the photoluminescence technique using coumarin as a probe molecule, to be produced on the irradiated Bi₂Fe₄O₉, and are scavenged on addition of ethanol and KI. The mechanisms involved are discussed in detail. Based on the experimental results, hydroxyl radicals and photogenerated holes are suggested to be the two main active species in the photocatalytic degradation of MB by Bi₂Fe₄O₉ nanoparticles.

Three kinds of carriers were utilised to prepare the corresponding sulfonated solid acid catalysts for the alkylation of two different thiophenic compounds (3-methylthiophene and 3-butylthiophene) with 1-hexene. Though the activity of the sulfonated solid acid catalysts was somewhat lower than that of liquid sulfuric acid, the solid acid catalysts had significant advantages in their easy separation, good recycling, selectivity and performance on reuse.