Theoretical study of the kinetics of reactions of the monohalogenated methanes with atomic chlorine

Abstract

Ab initio calculations at the G2 level were used in a theoretical description of the kinetics and mechanism of the hydrogen abstraction reactions from fluoro-, chloro- and bromomethane by chlorine atoms. The profiles of the potential energy surfaces show that mechanism of the reactions under investigation is complex and consists of two - in the case of CH3F+Cl - and of three elementary steps for CH3Cl+Cl and CH3Br+Cl. The heights of the energy barrier related to the H-abstraction are of 8–10 kJ mol−1, the lowest value corresponds to CH3Cl+Cl and the highest one to CH3F+Cl. The rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The kinetic equations derived in this studyandallow a description of the kinetics of the reactions under investigation in the temperature range of 200–3000 K. The kinetics of reactions of the entirely deuterated reactants were also included in the kinetic analysis. Results of ab initio calculations show that D-abstraction process is related with the energy barrier of 5 kJ mol−1 higher than the H-abstraction from the corresponding non-deuterated reactant molecule. The derived analytical equations for the reactions, CD3X+Cl, CH2X+HCl and CD2X+DCl (X = F, Cl and Br) are a substantial supplement of the kinetic data necessary for the description and modeling of the processes of importance in the atmospheric chemistry.

Experimental and Theoretical Study of the Kinetics and Mechanism of the Reaction of Chlorine Atoms with CH3CHClCH3 and CD3CDClCD3

“…Hence eqs and can be written as where the second component of the equations is a complex which goes into the transition state of every reaction. This approach was also proposed in, where some reactions of halogenomethanes were studied.…”

“…This type of reaction is more complex than indicated in expressions and . Our previous calculations regarding chloroethane and 1,2-dichloroethane did not confirm the intricate mechanism, but theoretical studies of the reaction of chloromethane of the same type clearly indicate that in these processes the complex with the noncovalent R–Cl···Cl interaction can be formed as the first step, followed by a transitional state and, finally, the obtaining of the products. The intermediate structure is probably very stable and has a significant impact on the course of the reaction.…”

“…It was assumed that the abstraction of the hydrogen atom could have a different course depending on which carbon atom it would be removed from. On the basis of the suppositions, 7 it was taken into account that this type of reaction might lead to the creation of a complex, where the attacking chlorine atom would interact with the chlorine atom bonded to the secondary carbon atom of2chloropropane. Such creation was confirmed by scans, IRC curves, and the other geometrical and energetic parameters.…”

“…limits, in the temperature range of 298−528.5 K. The values of k D determined experimentally and the Arrhenius line plotted according to eq 7 are shown in Figure2. The calculation of activation energy on the basis of our Arrhenius expression(7) gives the value of 1.54 kJ mol −1 for reaction 2.…”

Kinetic Aspects of Tetrahydrobenzo[b]pyran Formation in the Presence of Agar as a Green Catalyst: A Mechanistic Investigation

“…Thus, the best solution to meet this aim is simply to follow the disappearance of the starting material or appearance of a product as a function of time. This can be done by measuring the rate of a reaction at various concentrations of reactants and catalysts in order to determine the kinetic order with respect to a particular reactant and to establish an overall function which represents the rate law of a behavior reaction with a known rate constant [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] . Kinetics studies suggest many practical techniques to accomplish these measurements.…”