Thermochemical and Kinetics of CH₃SH + H Reactions: The Sensitivity of Coupling the Low and High-Level Methodologies

Abstract

The reaction system formed by the methanethiol molecule (CHSH) and a hydrogen atom was studied via three elementary reactions, two hydrogen abstractions and the C-S bond cleavage (CHSH + H → CHS + H (R1); → CHSH + H (R2); → CH + HS (R3)). The stable structures were optimized with various methodologies of the density functional theory and the MP2 method. Two minimum energy paths for each elementary reaction were built using the BB1K and MP2 methodologies, and the electronic properties on the reactants, products, and saddle points were improved with coupled cluster theory with single, double, and connected triple excitations (CCSD(T)) calculations. The sensitivity of coupling the low and high-level methods to calculate the thermochemical and rate constants were analyzed. The thermal rate constants were obtained by means of the improved canonical variational theory (ICVT) and the tunneling corrections were included with the small curvature tunneling (SCT) approach. Our results are in agreement with the previous experimental measurements and the calculated branching ratio for R1:R2:R3 is equal to 0.96:0:0.04, with k = 9.64 × 10 cm molecule s at 298 K.

One-Pot Catalytic Cleavage of C═S Double Bonds by Pd Catalysts at Room Temperature

“…The optimized structures of 1b and 1c are shown in Figure S41. Complex 1c possesses a D 3 h symmetry with two sulfur atoms at the center of the molecular, consistent with the reported crystal structure. − The optimized structures of three isomers for the intermediate of m / z = 482.0 are shown in Figure . We can observe the breaking of CS bond and the formation of CO bond in those three structures.…”

“… Obviously, the electron-donating ligand (X = CH 3 ) leads to an increase of the activation barrier, while electron-withdrawing ligand (X = CF 3 ) stabilizes the negative charge build-up in the transition state, thereby lowering the energy barrier of the rate-determining step of 13 to T4 (Figure S16). − Thus, the kinetic studies are consistent with the theoretical results . This is likely attribute to (1) the introduction of polar groups in γ-position of aromatic ring could compensate the loss of entropy and (2) the build-up of negative charge or the decrease of positive charge in the γ-position of aromatic ring in the rate-determining transition state …”

“…The kinetic parameters of the cleavage of single C–S bonds have been widely studied theoretically and experimentally to probe the mechanisms. − Nevertheless, to the best of our knowledge, the activation enthalpy (Δ H ⧧ ) and entropy values (Δ S ⧧ ) have never been reported for CS double bond activation. This may be due to the lack of successful systems for CS bond activation.…”

Theoretical study on the atmospheric reaction of CH3SH with O2

“…As a kind of highly reactive sulfur compound, CH 3 SH (methanethiol or methyl mercaptan) has been drawing long‐term attention because of its critical role in the atmospheric sulfur cycle . Significant amount of recent studies have focused on the reactions of CH 3 SH with series of species, such as H, O( 3 P), S( 3 P), OH, NO x (x = 1, 2, 3), X(X = F, Cl, Br), CN, XO(X = Br, I), O 3 , HOCl, CH 3 SLi, H 2 O 2 , HOO, and so on.…”

Thermochemical and Kinetics of the CH3OH + (4S)N Reactional System

“…In an earlier work, 36 we discussed the chemical kinetic results sensitivity to the coupling of the high-and low-level methodologies, concluding that the thermochemical values should be as close as possible between these methods to avoid excessive distortion in the reactional path and, consequently producing excessive amount of tunneling. In this context, comparing these results to the DFTs and MP2 ones, the B3LYP underestimates the barrier height and the MP2 overestimate it, as usual.…”