•A new three-dimensional potential energy surface including the antisymmetric Q3 normal mode of CS2 for Kr–CS2 and Xe–CS2 is constructed.•Both potentials with CS2 at both the ground (υ=0υ=0) and the first (υ=1υ=1) vibrational υ3υ3 excited states are found to have a T-shaped global minimum and two equivalent linear local minima.•The rovibrational energy levels are calculated as well as the band origin shifts and spectroscopic parameters are predicted.A three-dimensional ab initio intermolecular potential energy surfaces for the Kr–CS2 and Xe–CS2 complexes was constructed at the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] level with a large basis set plus midpoint bond functions (3s3p2d1f1g). The Q3Q3 normal mode for the υ3υ3 antisymmetric stretching vibration of the CS2 molecule was involved in the construction of the potential. Two vibrationally averaged potentials with CS2 at both the ground (υ=0)(υ=0) and the first excited (υ=1υ=1) υ3υ3 vibrational states were generated from the integration of the three-dimensional potential over the Q3Q3 coordinate. Both potentials have a T-shaped global minimum and two equivalent linear local minima. The radial discrete variable representation (DVR)/angular finite basis representation (FBR) method and the Lanczos algorithm were applied to calculate the rovibrational energy levels. The spectroscopic parameters based on the two averaged potentials were also predicted. The predicted band origin shifts are −0.7866 cm−1 for Kr–CS2 and −1.0658 cm−1 for Xe–CS2, respectively.

The first ab initio potential energy surface for Kr–HCCCN was calculated using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] with a large basis set containing bond functions. The potential has a T-shaped global minimum and a local linear minimum with the Kr atom facing the H atom. The radial discrete variables representation (DVR)/angular finite basis representation (FBR) method and the Lanczos algorithm were employed to calculate the rovibrational energy levels for three isotopomers 84Kr–HCCCN, 82Kr–HCCCN, and 86Kr–HCCCN. The spectroscopic constants for the ground and the first excited states of Kr–HCCCN were predicted.Graphical abstractHighlights► The first ab initio potential energy surface for the Kr–HCCCN complex is constructed. ► The potential has a T-shaped global minimum and a local linear minimum. ► The bound rovibrational energy levels and spectroscopic constants are calculated for Kr–HCCCN.

•The alcoholysis and thiolysis of four triesters have been studied using density functional theory.•The reactions proceed through a concerned mechanism or an associative mechanism.•The thiolysis are less favorable than the corresponding alcoholysis reactions.•The activation enthalpies in solution are higher than those in the gas phase.We have performed density functional theory calculations on the alcoholysis and thiolysis of four triesters with aryl and alkyl leaving groups in the gas phase and in solution. It is found that the alcoholysis of diethyl p-chlorophenyl phosphate proceeds through a concerned mechanism, while an associative mechanism is observed for the thiolysis reaction. The reactivity of diethyl phenyl phosphate and diethyl p-methylphenyl phosphate are similar, they react through an associative mechanism with both −OCH3 and −SCH3, though the second step of alcoholysis reaction has a low energy barrier. For triethyl phosphate, the alcoholysis and thiolysis reactions proceed by an associative mechanism, where the second step is the rate-determining step. The results show that the thiolysis of the four triesters are less favorable than the corresponding alcoholysis both in the gas phase and in solution, the enthalpies of all stationary points and the activation enthalpies for all the processes in solution are higher than those in the gas phase. Our calculations provide a comprehensive data set and allow re-interpretation of previous experimental and theoretical studies, and new experiment is proposed to trace reactions both in the gas phase and in solution.Graphical abstract

Density functional theory calculations have been used to explore the intrinsic reactivity for the methanolysis of paraoxon (native) and the analogous reactions with sulfur substitutions at key oxygen positions (bridging O2′, O2″, O5′ and nonbridging OP) in the gas phase and in solution. P-path involving the nucleophilic attack at the phosphorus atom and C-path involving the attack at the beta carbon atom are taken into account for the series of reactions. The reactions proceed through the SN2-type mechanism for both of the two pathways. It is found that except for the reaction of sulfur substitution at O5′ position the P-path is more favorable than the C-path kinetically. The products of the C-path are more accessible than the P-path thermodynamically, except for the reaction of sulfur substitution at the leaving (O2′ or O2″) position. The bond-forming is more advanced than the bond-breaking for all of the P-paths, while the bond-breaking is more advanced for all of the C-paths. The calculations provide a comprehensive data set, which are consistent with the previous experimental and theoretical studies and allow interpretation of measured thio effects.Graphical abstractHighlights► We studied the methanolysis of paraoxon and the effects of sulfur substitution. ► An SN2-type mechanism is observed for the P-path and C-path. ► Except for the S:O5′ reaction the P-path is more favorable than C-path kinetically. ► Except for the S:O2′(or O2″) reaction the products of C-path are more accessible. ► The results are consistent with the previous experimental and theoretical studies.

Density functional theory calculations have been used to investigate the intra-molecular attack of 2′-hydroxypropyl-p-nitrophenyl phosphate (HPpNP) and its analogous compound 2-thiouridyl-p-nitrophenyl phosphate (s-2′pNP). Bulk solvent effect has been tested at the geometry optimization level with the polarized continuum model. It is found that the P-path involving the intra-molecular attack at the phosphorus atom and C-path involving the attack at the beta carbon atom proceed through the SN2-type mechanism for HPpNP and s-2′pNP. The calculated results indicate that the P-path with the free energy barrier of about 11 kcal/mol is more accessible than the C-path for the intra-molecular attack of HPpNP, which favors the formation of the five-membered phosphate diester. While for s-2′pNP, the C-path with the free energy barrier of about 21 kcal/mol proceeds more favorably than the P-path. The calculated energy barriers of the favorable pathways for HPpNP and s-2′pNP are both in agreement with the experimental results.Graphical abstractThe intra-molecular attack at the phosphorus atom is more accessible for 2′-hydroxypropyl-p-nitrophenyl phosphate (HPpNP), while the intra-molecular attack at the beta carbon atom is more accessible for its analogous compound 2-thiouridyl-p-nitrophenyl phosphate (s-2′pNP).Download full-size imageHighlights► The geometries of the stationary points in water solution were optimized. ► The P-path is accessible for HPpNP, but for s-2′pNP the C-path is favorable. ► The calculated energy barriers are in agreement with the experimental results.

The mechanisms for C–F bond activation of the reaction of [Pt(PCy3)2] of C6F6, which yields metal–aryl product, have been characterized. Structures and energies for all of the stationary points in the [Pt(PMe3)2] and [Pt(PH3)(PH2Me)] models have been calculated using BP86 method. The calculated results show that the [Pt(PMe3)2] model is a more adequate for simulating the real system compared to the [Pt(PH3)(PH2Me)] model. The calculations also reveal that the concerted phosphine-assisted mechanism (pathway A) proceeding through the transfer of fluorine with the simultaneous shift of the Me group is the most accessible mechanism in the gas phase and in THF to form the Pt-aryl product, while the stepwise phosphine-assisted mechanisms (pathway B) and a mechanism via concerted oxidative addition (pathway C) proved less favorable. The further computational studies on the reaction of the model system [Pd(PMe3)2]) with C6F6 indicate the Pd-fluoroaryl product is more accessible than the Pd-aryl product.